“An excellent introduction into the newly emerging and exciting field of astrobiology. An essential, enjoyable and highly readable insight into life in its cosmic context.”
“Astrobiology involves the study of the origin and history of life on Earth, planets and moons where life may have arisen, and the search for extraterrestrial life. It combines the sciences of biology, chemistry, palaeontology, geology, planetary physics and astronomy. This textbook brings together world experts in each of these disciplines to provide the most comprehensive coverage of the field currently available.”
“This up-to-date resource is based on lectures developed by experts in the relevant fields and carefully edited by the leading astrobiologists within the European community. Aimed at graduate students in physics, astronomy and biology and their lecturers, the text begins with a general introduction to astrobiology, followed by sections on basic prebiotic chemistry, extremophiles, and habitability in our solar system and beyond.”
“The dynamic field of astrochemistry brings together ideas of physics, astrophysics, biology and chemistry to the study of molecules between stars, around stars and on planets. Astrochemistry: from Astronomy to Astrobiology provides a clear and concise introduction to this rapidly evolving multidisciplinary subject. Starting with the Molecular Universe, the text covers the formation of the elements, simple models of stars and their classification. It then moves on to draw on the theme of the Origins of Life to study interstellar chemistry, meteorite and comet chemistry as well as the chemistry of planets.”
“This highly interdisciplinary book highlights many of the ways in which chemistry plays a crucial role in making life an evolutionary possibility in the universe. Cosmologists and particle physicists have often explored how the observed laws and constants of nature lie within a narrow range that allows complexity and life to evolve and adapt. Here, these anthropic considerations are diversified in a host of new ways to identify the most sensitive features of biochemistry and astrobiology. Celebrating the classic 1913 work of Lawrence J. Henderson, The Fitness of the Environment for Life, this book looks at the delicate balance between chemistry and the ambient conditions in the universe that permit complex chemical networks and structures to exist.”
“Astrobiology: A Multidisciplinary Approach is the most comprehensive textbook available for emerging upper-level courses in astrobiology. Internationally renowned authority Jonathan Lunine gives students with a variety of backgrounds a solid foundation in the essential concepts of physics, chemistry, biology, and other relevant sciences to help them achieve a well-rounded understanding of the fascinating study of the origin of life, planetary evolution, and life in the cosmos.”
“Asteroids and comets: Every year, millions of these “stray bullets” streak through the skies, and tons of small meteorites strike our planet! Some 65 million years ago, dinosaurs were wiped off the face of the earth – in what many believe was the aftermath of a massive cosmic collision. Could something like this happen again? Scientists believe that the impact of an asteroid only a mile wide would be globally catastrophic.”
“Comet science is a field that has seen tremendous advances in recent years, far surpassing the knowledge reflected in the original Comets volume published as part of the Space Science Series in 1982. This new volume, with more than seventy contributing authors, contains the most extensive collection of knowledge yet assembled in the field. It will enable scientists involved in their study to make connections across disciplinary boundaries and will set the stage for discovery and new understanding in the coming years.”
“Comet Hale-Bopp defines a milestone event for cometary science: it is the first “really big” comet observed with modern equipment on the ground and from space and due to that; it is considered the new reference object in cometary sciences. At the beginning of a new era in spacecraft exploration of comets and five years after Hale-Bopp’s perihelion passage these proceedings of invited and contributed papers for IAU Colloquium 186 “Cometary Science after Hale-Bopp” review the state-of-the-art knowledge on comets, the icy, dusty and most primordial left-overs of the formation disk of our own solar system.”
“Around 700 BC an Assyrian scribe in the Royal Place at Nineveh made a copy of one of the most important documents in the royal collection. Two and a half thousand years later it was found by Henry Layard in the remains of the palace library. It ended up in the British Museum’s cuneiform clay tablet collection as catalogue No. K8538 (also called “the Planisphere”), where it has puzzled scholars for over a hundred and fifty years.
In this monograph Bond and Hempsell provide the first comprehensive translation of the tablet, showing it to be a contemporary Sumerian observation of an Aten asteroid over a kilometre in diameter that impacted Kofels in Austria in the early morning of 29th June 3123 BC.”
For many years academics in the historical sciences were content in their belief that terrestrial impacts by solid bodies from space was something that only happened in the very early history of our planet, whilst the average person had never heard the word ‘asteroid’. Then in 1980 the Nobel prizewinning physicist, Luis Alvarez, and his colleagues published their famous paper in “Science” which argued that a cosmic impact had led to the extinction of the dinosaurs. He showed that large amounts of the element iridium present in geological layers dating from about 65 million years BP had a cosmic origin, and proposed a radical theory that it was a massive ‘asteroid impact’ 65 million years ago which finally wiped out the dinosaurs.
Over the following decade interest began to rise in the idea of ‘terrestrial impacts’, and by 1990 most scientists at least accepted that the craters on our Moon were caused by impacts of cometary debris and asteroids of varying sizes, and not the volcanoes they had previously thought responsible.
As space exploration continued, the images sent back to Earth (especially by the Voyager spacecraft) allowed astronomers to build a picture of the sort of dynamic solar system first suggested by Victor Clube and Bill Napier in their groundbreaking books “Cosmic Serpent”(published 1982) and updated in “Cosmic Winter” (published 1990).
This was a new model of the solar system. One where regular influxes of comets from the various areas of space transitted by our solar system in its orbit through the galaxy suggested inevitable, and multiple, collisions with all the planetary bodies and their respective moons. Technologicl advances in space imaging have since shown a multitude of impact craters on all the inner planets and their moons. But some 12 years after the theories about the cosmic impact which led to the extinction of the dinosaurs were first proposed, the possibility of cometary bombardments still seemed something that belonged way back in the very early history of our solar system – even to most scientists.
It was on March 24 1993 that astronomers, husband and wife team Carolyn S. and Eugene M. Shoemaker, and David H. Levy, discovered a new comet in our solar system. Observations over the next few months determined that the comet was “at least temporarily” in orbit around Jupiter, and that on July 7 1992 the tidal forces of the largest planet in our solar system had caused the comet, by then named P/Shoemaker-Levy 9, to disintegrate. Over the next year or so astronomers on Earth observed the fragments proceeding around the Sun and head back on a collision course directly for Jupiter. From July 16 to 22nd 1994 they watched with awe as the 21 fragments bombarded the visible surface of Jupiter causing ‘fireballs 50 times the size of Earth’ and leaving huge scars on Jupiter’s southern hemisphere.
This was a wake-up call even for those who understood what was going on, and resulted in more funding being requested by astronomers to research the frequency of impacts throughout the solar system, but also to search for any evidence of past impacts on Earth. Following this event, the was an abrupt realisation by astonomers that ‘if it can happen to Jupiter now, it can also happen to Earth in the future’, and the search began in earnest to identify the orbital paths of all Earth-orbit-crossing celestial objects.
If anyone is in any doubt as to exactly how dangerous a place our planet occupies in the solar system they should simply look at our Moon. There for all to see, with the naked eye, and in even greater detail using a pair of good binoculars or a small telescope, are impact craters galore. There doesn’t appear to be one square mile of the lunar surface that is not pockmarked with impact craters, and while some are undoubtedly very ancient they also contain within their crater rims a myriad newer craters from much more recent impacts. The reason why there are so many visible craters on the Moon from ancient impacts was summed up well by astronomer, Duncan Steel, in his 1995 book,
“Rogue Asteroids and Doomsday Comets”:
“Craters are relatively swiftly eroded on Earth by rain, snow, and wind, whereas on the Moon they remain for eons until a new projectile happens to erase the scar left by some cousin countless millennia before.”
So this explains, partially, why there are so few visible craters on Earth. But raises the obvious question as to why we can’t see more given that, if our Moon is so cratered, surely our planet must be an even bigger target in the same area of the solar system? The answer is at once simple and also very complex. Firstly, there is approximately 71% of the surface area of the Earth covered with oceans – leaving just 29% dry land surface area. This gives a 3 to 1 chance that any incoming impactor will, if it doesn’t explode a few miles up like whatever happenned at Tunguska in 1908, impact one of the oceans and leave no easily visible trace.
Secondly, any crater on dry land would be at the mercy of the elements, and should there have been collisions with cometary debris, or asteroids, in the Amazon Basin, say, then vegetation would without doubt obscure them in a very short time indeed. But these are not the only factors, as Duncan Steel explained:
“The length of time that a crater will survive depends not only on the regions in which it is formed, but also on it’s size. Obviously a crater 50 kilometers across will last longer than a comparatibe pipsqueak just 100 meters in diameter. For example, in Australia there are 19 known craters – probably there are dozens more awaiting discovery – and of those, four are less than about 6,000 years old. Those are the four smallest however, all being less than 200 meters in diameter.”
At the time that Duncan Steel was writing “Rogue Asteroids and Doomsday Comets” in 1994/1995, there were then only about 140 known terrestrial impact craters. But in the years since then, spurred on by a new-found sense of urgency following the events on Jupiter in July 1994, the search picked up steam, and many more have been discovered.
The current tally is just uner 1000, and there is an interactive map of all the terrestrial impact craters accessible at the University of Arizona website. This is an excellent resource for anyone wishing to see just how many have so far been discovered on just the 29% of the surface area of our planet that is currenly dry land.
Another good resource for information about terrestrial impact craters which also has an interactive map is accessible at the University of New Brunswick Canadian website. The first paragraph or so of their introduction to the subject is worth quoting from here, as it puts the dynamic history of the solar system into a proper perspective:
“Until recently, impacts by extraterrestrial bodies were regarded as an interesting but, perhaps, not an important phenomenon in the spectrum of geological process affecting the Earth. Our concept of the importance of impact processes, however, has been changed radically through planetary exploration, which has shown that virtually all planetary surfaces are cratered from the impact of interplanetary bodies. It is now clear from planetary bodies that have retained portions of their earliest surfaces that impact was a dominant geologic process throughout the early solar system.
For example, the oldest lunar surfaces are literally saturated with impact craters, produced by an intense bombardment which lasted from 4.6 to approximately 3.9 billion years ago, at least a 100 times higher than the present impact flux. The Earth, as part of the solar system, experienced the same bombardment as the other planetary bodies.”
On this page we have tried to compile a photographic collection of impact craters on Earth to demonstrate just how many there actually are. Asteroids vary in their composition. Some are composed purely of stoney materials, some are composed of nickel & iron, while others have varying combinations of both. It should be understood that many of the asteroids which are made up of stoney materials do not survive the journey through our atmosphere. They explode in the upper atmosphere as the white-hot matter caused by friction upon entry hits the freezing cold air.
This has happened as recently as 1908 over the Tunguska region of Siberia, where the ‘air-burst’ caused an explosion the equivalent of many hundreds of nuclear bombs. Because the asteroid, or fragment of cometary debris, detonated in the upper atmosphere there was no impact crater to show what had happened, but many thousands of square miles of forest lands were completely flattened all around the detonation area.
The Tunguska airburst, Siberia – June 1908
How many times has this happened before? And how soon will it be before an something like this happens again? …
Click the image below or the headline above to acces this story
NASA
Imagine staring into the sky and seeing a tiny yellow dot, gradually getting closer. That dot doubles in size every second, until it slowly darkens the sky. You realize that this dot is actually the size of New York City and is screeching through the atmosphere faster than the speed of sound, coming right for you. This massive object will cause tsunamis, earthquakes and obliterate natural daylight for years … oh … and it will kill you.
Similar asteroid impacts have and will happen on numerous occasions in our earth’s history. Today we’ll show you the biggest impact craters by diameter.
100 Years Since The Tunguska Event
June 30, 1908
Taken during the 1927 Leonid Kulik expedition
This photograph shows trees destroyed by the blast nearly 20 years before
It has now been 100 years since the events of June 30, 1908, when a bolide of some description exploded over the Tunguska River region of Siberia. A conference to mark the anniversary took place in Moscow, Russia in 2008.
One hundred years ago, an explosion bigger than an atomic bomb blasted Tunguska, Siberia. We still don’t know what caused it, but there are plenty of theories!
In 1991, Italian scientists still found evidence of fallen trees near the blast site
University of Bologna
Early on the morning of June 30, 1908, a massive explosion rocked the Siberian wilderness flattening more than 2,000 square kilometres of forest.
Villagers 100 kilometres away from the Podkamennaya Tunguska river basin reported seeing a fireball in the sky, feeling intense heat, hearing loud thumps and being thrown off their feet.
‘The split in the sky grew larger, and the entire Northern side was covered with fire. At that moment I became so hot that I couldn’t bear it, as if my shirt was on fire; from the northern side, where the fire was, came strong heat.’
‘I wanted to tear off my shirt and throw it down, but then the sky shut closed, and a strong thump sounded, and I was thrown a few yards’, reported one villager.
The explosion lit up the sky as far away as London for several days.
Nearly two decades later, the first expedition into the area led by Russian meteorite specialist Leonid Kulik found a region of scorched trees 50 km in diameter, but no crater.
It’s now believed that the Tunguska event — as it’s now known — was hundreds of times more powerful than the atomic bomb dropped on Hiroshima
Tunguska has long fascinated scientists, enthusiasts and sci-fi fans. Over the years, the mystery of the event has prompted a number of theories with varying degrees of scientific plausibility. These have ranged from a meteorite to the crash of an alien spacecraft; an explosion of methane or the result of Nikola Tesla’s experiments with electricity near New York.” [Full Story]
Geographic Distribution of Known Impact Structures
Lunar & Planetary Institute
Terrestrial Impact Craters
News & New Discoveries 2006 to 2009:
“A Sydney-based astronomer has used ancient culture and modern technology to identify a meteorite crater in central Australia.
Macquarie University PHD candidate Duane Hamacher has spent the past 18 months researching how Aboriginal people have incorporated the night sky into their culture.
He says he used an Arrernte dreaming story and Google maps to find a crater at Palm Valley, west of Alice Springs, that had been unknown to geologists.
“The particular Western Arrernte story talked about a star that fell from the sky, making a noise like thunder and crashed into a waterhole in Palm Valley,” he said.
“What I decided to do was look on Google Earth, Google Maps and check that area out and see if there was any impact crater that could be seen.” [Full Story]
“On October 8, 2009 about 03:00 Greenwich time, an atmospheric fireball blast was observed and recorded over an island region of Indonesia.
The blast is thought to be due to the atmospheric entry of a small asteroid about 10 meters in diameter that, due to atmospheric pressure, detonated in the atmosphere with an energy of about 50 kilotons (the equivalent of 100,000 pounds of TNT explosives).
The blast was recorded visually and reported upon by local media representatives. See the YouTube video:
A report from Elizabeth Silber and Peter Brown at the University of Western Ontario indicates that several international very-long wavelength infrasound detectors recorded the blast and fixed the position near the coastal city of Bone in South Sulawesi, island of Sulewesi.” [Full Story]
“Geologists in Bangalore and Nagpur on Tuesday confirmed the significance of the Shiva Basin beneath the Indian Ocean near Bombay High
which was proposed to be the largest crater on the planet by a professor of Indian origin in Texas.
The Geological Survey of India and IIT Bombay have already begun intensive research on the crater to understand its nature and formation.
Prof. Sankar Chatterjee, in a paper presented at the Geological Society of America in Portland earlier this month, said this basin, a submerged depression on the west coast of India, is the largest crater.
The 40-km wide crater is thought to have been formed by a meteorite that crashed into the Earth 65 million years ago.
The meteorite was travelling at 58,000 miles per hour and was also responsible for killing dinosaurs that lived at that time, he claimed.” [Full Story]
“A mysterious basin off the coast of India could be the largest, multi-ringed impact crater the world has ever seen.
And if a new study is right, it may have been responsible for killing the dinosaurs off 65 million years ago.
please click on the image below to access a larger image
Geological Society of America
Sankar Chatterjee of Texas Tech University and a team of researchers took a close look at the massive Shiva basin, a submerged depression west of India that is intensely mined for its oil and gas resources.
‘If we are right, this is the largest crater known on our planet’, Chatterjee said. ‘A bolide of this size, perhaps 40 kilometers (25 miles) in diameter creates its own tectonics.’
By contrast, the object that struck the Yucatan Peninsula, and is commonly thought to have killed the dinosaurs was between 8 and 10 kilometers (5 and 6.2 miles) wide.” [Full Story]
“Refined calculations of the asteroid Apophis’s path show it is far less likely smash into Earth in 2036 than was previously thought.
Earlier calculations put the probability of a collision at one in 45,000; the revised estimate puts the odds at one in 250,000.
Rest easy: the asteroid only has a four in a million chance of Earth impact
SPL / BBC News
Researchers from the US space agency Nasa showed that in 2029, Apophis will pass within just 30,000km of Earth.
The work will be presented at a meeting of the American Astronomical Society.
The new calculations are based on more precise measurements of the asteroid’s position based on images captured by Dave Tholen at the University of Hawaii, supplemented by further measurements by telescopes in Arizona and Puerto Rico.” [Full Story]
“Meteorites recently striking Mars have exposed deposits of frozen water not far below the Martian surface.
Pictures of the impact sites taken by NASA’s Mars Reconnaissance Orbiter show that frozen water may be available to explorers of the Red Planet at lower latitudes than previously thought.
A fresh, 6-meter-wide, 1.33-meter-deep crater on Mars photographed on Oct. 18, 2008, and again on Jan. 14, 2009, by Mars Reconnaissance Orbiter’s HiRISE camera. The bright material is ice, which fades from Oct. to Jan. because of sublimation and obscuration by settling dust.
Science @ NASA
‘This ice is a relic of a more humid climate from perhaps just several thousand years ago’, says Shane Byrne of the University of Arizona, Tucson.
Byrne is a member of the team operating the orbiter’s High Resolution Imaging Science Experiment, or HiRISE camera, which captured the unprecedented images. Byrne and 17 co-authors report the findings in the Sept. 25 edition of the journal Science.
‘We now know we can use new impact sites as places to look for ice in the shallow subsurface’, adds Megan Kennedy of Malin Space Science Systems in San Diego, a co-author of the paper and member of the team operating the orbiter’s Context Camera.
So far, the camera team has found bright ice exposed at five Martian sites with new craters that range in depth from approximately half a meter to 2.5 meters (1.5 feet to 8 feet). The craters did not exist in earlier images of the same sites.” [Full Story]
“When a comet crashed into the Yucatan Peninsula 65 million years ago, all hell broke loose.
Scientists have guessed at the scene: a world enshrouded in ashen darkness leftover from the cosmic impact that left almost nothing — including the dinosaurs — standing.
But a new study shows that in western Europe at least, the effects were far less terrifying.
Fossil leaves from four million years after the impact show that plants and insects had made a full recovery.
‘It looks like a healthy ecosystem at 61 million years ago’, said Torsten Wappler of the University of Bonn. ‘You have a huge diversity of plants, and plant and insect interactions.’
Wappler and a team of researchers tallied up the holes and chew marks insects left in fossil leaves unearthed in France. Depending on the patterns of munching, they could often distinguish which species fed on a particular leaf.” [Full Story]
“It looks inconsequential enough, the faint little spot moving leisurely across the sky. The mountain-top telescope that just detected it is taking it very seriously, though. It is an asteroid, one never seen before.
Rapid-survey telescopes discover thousands of asteroids every year, but there’s something very particular about this one.
The telescope’s software decides to wake several human astronomers with a text message they hoped they would never receive. The asteroid is on a collision course with Earth. It is the size of a skyscraper and it’s big enough to raze a city to the ground.
Oh, and it will be here in three days.
Far-fetched it might seem, but this scenario is all too plausible.
Certainly it is realistic enough that the US air force recently brought together scientists, military officers and emergency-response officials for the first time to assess the nation’s ability to cope, should it come to pass.
They were asked to imagine how their respective organisations would respond to a mythical asteroid called Innoculatus striking the Earth after just three days’ warning.
The asteroid consisted of two parts: a pile of rubble 270 metres across which was destined to splash down in the Atlantic Ocean off the west coast of Africa, and a 50-metre-wide rock heading, in true Hollywood style, directly for Washington DC.
The exercise, which took place in December 2008, exposed the chilling dangers asteroids pose. Not only is there no plan for what to do when an asteroid hits, but our early-warning systems – which could make the difference between life and death – are woefully inadequate.” [Full Story]
“In a clear case of geology and archaeology complementing each other, scientists have studied the most recent limestone deposits that filled the Chicxulub crater in Mexico, providing accurate dating of the rocks and a valuable basis for archaeologists to research the ancient Maya.
The Chicxulub crater is one of the world’s most famous asteroid craters, which is believed to have put an end to the dinosaurs and helped mammals to flourish.
Together with an Anglo-American team, an ETH Zurich researcher has studied the most recent deposits that filled the crater.
Drifting through space for eons, they eventually come into Earth’s gravity well, and fall to the ground. The most infamous example of this was a small rock found in Antarctica in 1984, which was later discovered to be Martian
Research work has focused mainly on the structure of the crater, which has been buried in a layer of sediment up to two kilometres thick since its formation.
Little is known about the sediments close to the surface.” [Full Story]
“Rocks from space fall to Earth all the time. Meteorite fragments are so common that they turn up in jewelry.
Some of these fragments have been found to come from the Moon and Mars, giving us a very cheap form of sample retrieval.
They’re blown off the surface of these worlds when a large object impacts the surface, creating a massive explosion.
It’s generally accepted that the Moon itself was formed when a planet-sized object collided with the early Earth, scattering material into space that later coalesced into the Moon. Both of these twin worlds now hold fragments of the original Earth and the small planet.
Space Daily
Drifting through space for eons, they eventually come into Earth’s gravity well, and fall to the ground. The most infamous example of this was a small rock found in Antarctica in 1984, which was later discovered to be Martian
Analysis of this meteorite led to the controversial suspicion that it contained microfossils, possibly our first evidence of life beyond Earth.
The Martian fossil theory has now been generally discredited, but it pointed to the importance of studying material from other worlds.
There’s another side to the rocks from space story that isn’t as well known. Some fragments of Earth are believed to have been deposited on other worlds.” [Full Story]
“Meteors that are large enough to survive the trip through the Earth’s atmosphere are usually completely destroyed during impact.
Those meteorites that hit on land leave behind an impact crater. On Earth, wind, water, and vegetation rapidly (on geologic times scales) erase craters.
With few exceptions, even the largest craters are eventually destroyed by the processes of plate tectonics. On the Moon, however, craters are virtually permanent.
Impacts have shaped the Earth and Moon since early in the history of the solar system. In fact, the Moon likely formed when a proto-planet (likely the size of Mars) crashed into the Earth over 4.5 billion years ago.
The only weathering is caused by later impacts and the solar wind. A ‘fresh’ crater on the Moon can be hundreds of millions of years old.
The collision sprayed material from the two worlds into orbit around the Earth. The debris coalesced and formed the Moon.
This isn’t the first time scientists have theorized that the ingredients for life on Earth could have been delivered. Comets and asteroids both have been proposed as carriers of water as well as organic compounds to Earth.” [Full Story]
“A British research team suggests that a massive bombardment billions of years ago delivered enough water and carbon dioxide to create the conditions for life to form.
A massive bombardment of meteorites billions of years ago could have brought in enough water and carbon dioxide to jump-start the chemistry that let the Earth develop into the garden spot of our solar system.
By studying meteorites and other evidence from this bombardment, a team of researchers at Imperial College in England has calculated that the meteorites could have carried in as much as 10 billion tons of water vapor and carbon dioxide to the young Earth every year for millions of years.
The release of the greenhouse gas carbon dioxide could have trapped more energy from sunlight to make Earth and Mars warm enough to sustain liquid oceans.
That amount of water and carbon dioxide would have been enough to set off a greenhouse effect that eventually made the Earth warm and wet enough to harbor plants and creatures.
This isn’t the first time scientists have theorized that the ingredients for life on Earth could have been delivered. Comets and asteroids both have been proposed as carriers of water as well as organic compounds to Earth.” [Full Story]
“Large bombardments of meteorites approximately four billion years ago could have helped to make the early Earth and Mars more habitable for life by modifying their atmospheres, suggests the results of a paper published today in the journal Geochimica et Cosmochima Acta.
When a meteorite enters a planet’s atmosphere, extreme heat causes some of the minerals and organic matter on its outer crust to be released as water and carbon dioxide before it breaks up and hits the ground.
A fragment of the Murchison meteorite was analysed by researchers
Imperial College London
Researchers suggest the delivery of this water could have made Earth’s and Mars’ atmospheres wetter.
The release of the greenhouse gas carbon dioxide could have trapped more energy from sunlight to make Earth and Mars warm enough to sustain liquid oceans.
In the new study, researchers from Imperial College London analysed the remaining mineral and organic content of fifteen fragments of ancient meteorites that had crashed around the world to see how much water vapour and carbon dioxide they would release when subjected to very high temperatures like those that they would experience upon entering the Earth’s atmosphere.
The researchers used a new technique called pyrolysis-FTIR, which uses electricity to rapidly heat the fragments at a rate of 20,000 degrees Celsius per second, and they then measured the gases released.” [Full Story]
“When a scientific principle is common knowledge even in grammar schools, you know it’s long since crossed the line from theory to established fact.
That’s the case with dinosaur extinction.
Some 65 million years ago — as we’ve all come to know — an asteroid struck the Earth, sending up a cloud that blocked the sun and cooled the planet.
That, in turn, wiped out the dinosaurs and made way for the rise of the mammals. The suddenness with which so many species vanished after the 65-million-year mark always suggested a single cataclysmic event, and the 1978 discovery of a 112-mi., 65-million-year-old crater off the Yucatán peninsula near the town of Chicxulub seemed to seal the deal.
An artist’s drawing of an asteroid headed towards Earth
Denis Scott/CORBIS
Now, however, a new study in the Journal of the Geological Society throws all of that into question. The asteroid impact and the dinosaur extinction, argue the authors, may not have been simultaneous, but rather may have occurred 300,000 years apart.
That’s an eye-blink in geological time, but it’s a relevant eye-blink all the same, one that occurred at just the right moment in ancient history to have sent the extinction theory entirely awry. [See pictures of meteors striking the earth]
The controversial new paper was written by geoscientists Gerta Keller of Princeton University and Thierry Addate of the University of Lausanne, in Switzerland — and both researchers knew that challenging the impact doctrine would not be easy.
The asteroid charged with killing the dinosaurs, after all, left more than the Chicxulub crater as its calling card.
But Keller and Addate worried that we were misreading both the geological and fossil records. They conducted surveys at numerous sites in Mexico, particularly at a spot called El Peñón, very near the impact crater.
They were especially interested in a 30-ft. layer of sediment just above the iridium layer. That sediment, they calculate, was laid down at a rate of about 0.8 in. to 1.2 in. per thousand years, meaning that the entire 30 feet took 300,000 years to settle into place.” [Full Story]
“Debris from an asteroid tracked as it fell to Earth has been recovered by scientists for the first time, says a report in the science journal Nature.
Nearly 50 fragments of the asteroid were collected from the desert in Sudan where it fell last October.
The fragments showed evidence of being at extremely high temperatures
NASA/Peter Jenniskens
Scientists say the discovery offers a unique opportunity to study the asteroid’s route and chemical make-up. It will also give new insights into how to tackle any larger asteroids heading towards Earth in the future.
The car-sized lump of rock, known as 2008 TC3, was detected by astronomers in the US state of Arizona in October last year.
It was tracked by telescopes around the world until it disintegrated in the atmosphere above the Nubian desert region of Sudan.” [Full Story]
“Scientists have discovered only the second example of a meteorite impact that occurred at the same time as massive volcanic activity, in research published in the Journal of the Geological Society the week of Jan 12.
The first time such a coincidence was observed, at the Cretaceous-Tertiary boundary, was the catastrophic event thought to be responsible for the extinction of the dinosaurs, 65 million years ago.
This new event, uncovered after the 17 km diameter Logoisk impact structure in Belarus was precisely dated, is thought to have taken place around 30 million years ago. The crater was dated using argon isotopes, and found to have occurred at a similar time to a period of massive volcanism known as the Afro-Arabian flood volcanism, which started in NW Yemen at around 30.9 Mya, and SW Yemen at around 29.0 Mya.
The impact also coincides broadly with a period of sudden global cooling and sea level fluctuation.
The researchers, led by Sarah Sherlock at the Open University, argue that massive volcanic eruptions and meteorite impacts are likely to have coincided much more frequently than has previously been thought, but because the preservation of impact craters on Earth is poor much of the evidence for these coincidences is lost.” [Full Story]
“Glaciologists have long agreed that many of the first visible signs of global warming would appear in Earth’s frozen regions. This knowledge has focused attention on the polar regions and how they might change in the near future.
To understand how the physical and ecological conditions at high latitudes might change, scientists must understand how the current conditions developed.
Detailed records of climate change over the past few million years, however, are sparse, in part because the landscape has been repeatedly scoured by massive ice sheets.
One area that offers a glimpse into the Arctic’s distant past is the lake bed below Lake El’gygytgyn. Lying some 100 kilometers (60 miles) north of the Arctic Circle in eastern Russia, Lake El’gygytgyn rests inside an impact crater.
The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite took this picture of the crater and its surroundings on August 18, 2008. In this false-color image, red indicates vegetation, gray-brown indicates bare land, and deep blue indicates water.” [Full Story]
A screen grab from Google Earth showing the meteorite crater, dead centre. Inset: Mike Fry
Chris Watkins for The Age, Australia/Google Earth
“A retired geologist searching on Google Earth for a place to mine opals may have discovered something much bigger: a meteorite crater in outback NSW.
Mike Fry was using the Google site last month to survey terrain when he saw an unusual structure in the red dust.
‘The circular nature of this thing struck me’, Mr Fry said. ‘It was so distinctive, I was gobsmacked.’
Mr Fry, who earned a degree in geology from the University of New Mexico before coming to Australia 44 years ago to mine opals and gold, drove 11 hours to the site, about 10 kilometres north-east of White Cliffs, to take a closer look.
‘I have walked around it’, he said, estimating his ‘crater’ was at least two kilometres across. ‘There is a steep slope on the eastern side, which rises 30 to 50 metres above the floor.’ [Full Story]
“Geologists often study features on Earth, such as impact craters, to gain insight into processes that occur on other planets. On Earth, more than 150 impact craters have been identified on the continents, but only a few of these are classified as double impact craters.
One such pair, the Arkenu Craters in northern Africa, is shown in this image. Arkenu 1 and 2 are double impact structures located in eastern Libya in the Sahara Desert (22 degrees, 4 minutes North; 23 degrees, 45 minutes East). Their respective diameters are approximately 6.8 and 10.3 kilometers (4.2 and 6.4 miles).
The craters are unusual in that they both exhibit concentric annular ridge structures (white circles in the image outline the position of the outermost visible ridges). In many terrestrial craters these features are highly eroded and no longer visible.
While the circular structure of these features had been noted, the impact origin hypothesis was strengthened in December 2003 when a field team observed shatter cones—cone-shaped features in rocks created by the shock generated during impact. The field research team also observed large outcrops of impact breccias—a jumble of rock fragments generated at the impact site that are now cemented together into an identifiable rock layer.
One theory of the craters’ formation proposes they were the result of two impactors, each approximately 500 meters in diameter. The age of the impact event has been dated as having occurred less than 140 million years ago.”
METEOSAT-8 catches the 2008 TC3 fireball
METEOSAT-8/The Planetary Society
“It seems that no one in Sudan was able to record the 2008 TC3 fireball; the only image I’ve seen that was shot from the ground was one very tiny pixel in the sky seen from a beach in Egypt.
But in this day and age, there are always eyes in the sky on practically every point on Earth, and, through good fortune, the METEOSAT-8 spacecraft scanned the globe at the moment that the asteroid was putting on its show.
First, a little context: the METEOSAT satellites are geostationary weather satellites operated by a European consortium called EUMETSAT. The METEOSATs are among the whole-Earth-observing spacecraft I list on my ‘Whole-Earth views from Geostationary Satellites’ web page. METEOSAT-8 was launched in August 28, 2002.
In April of last year, it was relegated to backup status, replaced in active status by METEOSAT-9; both orbit Earth in a geostationary position near about 9°E, which puts all of Africa and Europe in view. As of May 13, 2008, EUMETSAT started using METEOSAT-8 in a ‘rapid scanning’ mode, in which it scans the globe once every five minutes. So it was well positioned to spot the fiery atmospheric entry of 2008 TC3.
Okay, so here’s the view of the fireball as seen through an infrared instrument on METEOSAT-8, which records the temperature of the surfaces it scans. The temperature scale on the right is in Kelvin; 273 Kelvin corresponds to 0 Celsius. Most of the land in this desert region of Earth is quite warm, with a few cold clouds to the southwest. And then there’s the orange flare of the fireball.” [Full Story]
“Those of us that study one aspect or another of the Earth impact hazard are sometimes asked, ‘If one of these dangerous space rocks really is on course for Earth, how much warning will we have before it collides with our planet?’ The answer has been – and still is – that the most probable situation is a warning time of just a few seconds. That is, despite the excellent work of telescopic ‘Spaceguard surveys’, most objects capable of causing a serious amount of damage have not yet been discovered. So the first the inhabitants of Earth would know is when the intruder from space starts to vaporise on its high speed passage through the atmosphere, producing an immense fireball. Admire the brief, spectacular show, and hope it lands or explodes far enough away that you escape the worst effects.
Astronomers’ progress in finding the larger near-Earth objects in interplanetary space, although incomplete, has been substantial. As these objects, on impact, could produce devastation on a global scale, it seems fair to regard this part of the task as the most important. But what of lesser impactors whose effects on impact would still be destructive, albeit on a localised – up to continental – scale? These objects have lesser potential consequences, but they are much greater in number than the larger bodies. Not globally damaging, but more likely to happen.
The terminal explosion of the ‘Tunguska bolide’, an event whose centenary is this year, flattened trees covering an area of two thousand square kilometres in the middle of Siberia. Back in 1908, the Tunguska object, which would have been the size of a large building, was not of course seen out in space before it hit the atmosphere creating a fireball as bright as the Sun. A hundred years later, a handful of Tunguska-sized asteroids have been spotted by telescopes, but most remain unseen.
The asteroid designated ‘2008 TC3’, which made the news on October 6th before colliding with the Earth on October 7th was too small to constitute a part of the ‘Earth impact hazard’. Such asteroids, around the size of a car, are generally prevented from reaching the ground intact by the atmosphere, which acts as a shield. 2008 TC3, for example, finally exploded in the atmosphere above Sudan. But this asteroid represents a world first in a way that has exciting implications for studies of the near-Earth environment.”
“The moon’s pockmarked face stands as mute witness to the chaos that reigned in the solar system in the eons following the Big Bang, when objects flying at unimaginable speeds slammed repeatedly into the lunar surface.
Such impacts surely occurred at least as frequently early in Earth’s history, when the impact rate was 1,000 times higher than it is now. But the results of those ancient events aren’t nearly as obvious.
Craters can lie hidden under deep sediments, eroded by wind and weather until unrecognizable, and in some cases, be erased almost entirely from view.
On this planet, the crater hunter’s job is akin to a crime scene investigator, looking for various clues that add up to the irrefutable existence of a crater.
In recent years, crater sleuths have finally begun to succeed at finding some of the Earth’s most significant impact craters and unraveling the secrets they hold.” [Full Story]
“Lake Jänisjärvi is a roughly oval-shaped lake, some 13 by 17 kilometers (8 by 11 miles) across, in northwestern Russia, near the Finnish border. The basin for this lake was formed hundreds of millions of years ago by a meteorite impact.
On September 5, 1999, NASA’s Landsat-7 satellite captured this image of Lake Jänisjärvi and its surroundings. This late-summer shot shows a lush green landscape free of snow and ice.
Land around the lake appears in varying shades of green, interrupted by tan and pink swaths of cleared (probably agricultural) land, particularly in the east. The lake itself is deep blue, dotted with diminutive islands.
A close look at the lake’s ragged contours indicates that the this water body is connected to many others in the area. The tiny tributary exiting this lake’s southern edge meanders toward Lake Ladoga to the south.” [Full Story]
“The craters discovered recently near Dukhan, 90km west of Doha, are of unusual shape, according to Qatari astronomical observer and active member of Qatar Scientific Club Sheikh Salman bin Jabor Al Thani.
Images of these craters, believed to have been formed following meteor impact nearly seven decades ago, were presented by Sheik Salman at Doha Scientific Club on Sunday.
The craters discovered have an upward curve rather than a depression as in normal craters. The soft nature of the sand in the site can be accounted for this shape.
Pillar like structures of sand have been found in the crater. The studies on the sand structures have found that they were formed very fast rather than over time. The high temperature during the impact, which might have led to the boiling of the water salt and sand, can explain the formation of these structures.
The area was marshy when the meteorite hit. There had been stories of camels being sucked into the earth from this place long back. Now due to industrialization, the water content of the area has decreased; most have dried up and become deserts’, Sheikh Salman said. The studies have shown that there is a high density in salt content in the area even today.” [Full Story]
“It is a mystery which has puzzled generations of geologists – the origins of a layer of stratified rock trapped in the sediments which now form part of the coastline of north-west Scotland.
Scientists suspected for years that the curious seam could have been formed by volcanic activity millions of years ago.
But it was revealed yesterday that the 40-mile long rock layer was formed when the biggest meteorite ever to strike what is now the British Isles hit the Earth close to present-day Ullapool with the force of a 145,000 megaton bomb.
Geologists at Aberdeen and Oxford universities, who made the discovery, believe that the rock was formed by ejecta – material which was forced out of the Earth – by the meteorite, it hit 1.2 billion years ago.
The meteorite, which is thought to have measured up to 1km across, would have formed an impact crater up to 10km in diameter, but the material ejected by the impact spread out for at least 50km.
Ken Amor, one of the leaders of the team of geologists involved in the discovery, said: ‘This is the most spectacular evidence for a meteorite impact within the British Isles to date, and what we have discovered about this meteorite strike could help us understand the ancient impacts that shaped the surface of other planets, such as Mars.'” [Full Story]
“It’s lucky for the good burghers of Ullapool in Scotland that they weren’t around 1.2 billion years ago, because it was around then that the biggest meteorite ever to hit the British Isles would have made a bit of a dent in local house prices.
That’s according to the combined forces of the University of Oxford and the University of Aberdeen, who say that ‘unusual rock formations’ previously thought to have volcanic origins are actually the debris ejected from a meteorite strike which threw material over an area 50km across.
The volcanic theory has always had geologists scratching their heads, since there are ‘no volcanic vents or other volcanic sediments nearby’. The researchers moved in for the kill by taking rock samples in 2006, and have now published their revelations in the journal Geology.
Ken Amor of Oxford Uni’s Department of Earth Sciences, explained: ‘Chemical testing of the rocks found the characteristic signature of meteoritic material, which has high levels of the key element iridium, normally only found in low concentrations in surface rocks on Earth. We found more evidence when we examined the rocks under a microscope; tell-tale microscopic parallel fractures that also imply a meteorite strike.'” [Full Story]
“The craters discovered recently near Dukhan, 90km west of Doha, are of unusual shape, according to Qatari astronomical observer and active member of Qatar Scientific Club Sheikh Salman bin Jabor Al Thani.
Images of these craters, believed to have been formed following meteor impact nearly seven decades ago, were presented by Sheik Salman at Doha Scientific Club on Sunday.
The craters discovered have an upward curve rather than a depression as in normal craters. The soft nature of the sand in the site can be accounted for this shape.
Pillar like structures of sand have been found in the crater. The studies on the sand structures have found that they were formed very fast rather than over time. The high temperature during the impact, which might have led to the boiling of the water salt and sand, can explain the formation of these structures.
‘The area was marshy when the meteorite hit. There had been stories of camels being sucked into the earth from this place long back. Now due to industrialization, the water content of the area has decreased; most have dried up and become deserts’, Sheikh Salman said. The studies have shown that there is a high density in salt content in the area even today.” [Full Story]
“Next time you’re virtually roaming Google Earth, make sure you take a close look at any unusual landforms.
Geologist Arthur Hickman did just that, and is now the proud parent of the Hickman Crater, a meteorite crater in the Hamersley Ranges.
Dr Hickman, from the Geological Survey of Western Australia, was using Google Earth to look for iron ore when he noticed an unusually circular structure.
He sent a Google Earth picture of the structure to his colleague Dr Andrew Glickson at the Australian National University, who later visited the area and confirmed that Dr Hickman had found a particularly well preserved meteorite crater.
The crater is 270m across <(around the size of the MCG) and is just 35km north of Newman, but hadn’t been previously discovered.” [Full Story]
“The area where a meteorite landed in Puno, approximately 800 miles from Lima, has been declared a National Cultural and Natural Heritage Site by the Regional Government of Puno, Peru, said the region’s president, Pablo Hernán Fuentes Guzmán.
The regional president explained that the meteorite crater was being declared a part of Peru’s heritage to preserve it and keep it safe from locals and foreigners that “want to get their hands on it”.
The meteorite, which was found to be a chondrite, landed in the town of Carancas near the Peru-Bolivia border on September 15, leaving a crater approximately forty feet in diameter.” [Full Story]
A meteorite the size of four Wal-Mart Supercenters likely plunged into what we now know as the Delta millions of years ago, according to a geologist and his teenage son.
The duo recently found what they believe to be a 3.4-mile-wide crater buried far beneath the asparagus fields of Victoria Island, about 15 miles west of Stockton.
The discovery was entirely by accident. Geologist Bennett Spevack of San Diego works for a firm that was drilling in search of oil; while poring over data, he found a circular depression. [Full Story]
Planetary scientists have found evidence of a meteor impact much larger and earlier than the one that killed the dinosaurs – an impact that they believe caused the biggest mass extinction in Earth’s history.
The 300-mile-wide crater lies hidden more than a mile beneath the East Antarctic Ice Sheet. And the gravity measurements that reveal its existence suggest that it could date back about 250 million years – the time of the Permian-Triassic extinction, when almost all animal life on Earth died out.
Its size and location – in the Wilkes Land region of East Antarctica, south of Australia – also suggest that it could have begun the breakup of the Gondwana supercontinent by creating the tectonic rift that pushed Australia northward. [Full Story]
Researchers from Boston University have discovered the remnants of the largest crater of the Great Sahara of North Africa, which may have been formed by a meteorite impact tens of millions of years ago. Dr. Farouk El-Baz made the discovery while studying satellite images of the Western Desert of Egypt with his colleague, Dr. Eman Ghoneim, at BU’s Center for Remote Sensing.
The double-ringed crater – which has an outer rim surrounding an inner ring – is approximately 31 kilometers in diameter. Prior to the latest finding, the Sahara’s biggest known crater, in Chad, measured just over 12 kilometers.
According to El-Baz, the Center’s director, the crater’s vast area suggests the location may have been hit by a meteorite the entire size of the famous Meteor (Barringer) Crater in Arizona which is 1.2 kilometers wide. [Full Story]
Terrestrial & Solar System
Impacts and Impact Craters
Below are some images of the larger known asteroids
Asteroid Eros
NEAR, JHU APL, NASA
“Several spacecraft have orbited or landed on asteroids and sent pictures of these bodies back to Earth. The NEAR Shoemaker mission, launched in 1996, was the first spacecraft to land on an asteroid, touching down on Eros on February 12, 2001.”
Asteroid 253 Mathilde
NEAR, JHU APL, NASA
On June 27, the NEAR (for Near Earth Asteroid Rendezvous) spacecraft, traveling some 36,000 kilometers per hour, streaked past an asteroid named Mathilde far beyond the orbit of Mars. It was just a brief encounter along a long journey to a different asteroid, Eros.
“Liquid water, carbon-based molecules and a relatively stable environment are critical elements for life. Comets and asteroids can bring water and the chemicals on which life is based, but can also bring widespread destruction. If future impacts are inevitable, what should we do?”
“Around 700 BC an Assyrian scribe in the Royal Place at Nineveh made a copy of one of the most important documents in the royal collection. Two and a half thousand years later it was found by Henry Layard in the remains of the palace library. It ended up in the British Museum’s cuneiform clay tablet collection as catalogue No. K8538 (also called “the Planisphere”), where it has puzzled scholars for over a hundred and fifty years. In this monograph Bond and Hempsell provide the first comprehensive translation of the tablet, showing it to be a contemporary Sumerian observation of an Aten asteroid over a kilometre in diameter that impacted Kofels in Austria in the early morning of 29th June 3123 BC.”
“This volume synthesizes 16 years of geological and geophysical studies which document an 85-km-wide impact crater buried 500 m beneath Chesapeake Bay in south eastern Virginia, USA. The authors integrate extensive seismic reflection profiling and deep core drilling to analyze the structure, morphology, gravimetrics, sedimentology, petrology, geochemistry, and paleontology of this submarine structure. Of special interest are a detailed comparison with other terrestrial and extraterrestrial craters, as well as a conceptual model and computer simulation of the impact. The extensive illustrations encompass more than 150 line drawings and core photographs. An accompanying CD-ROM includes selected seismic profiles, scaled cross sections, detailed maps, and downhole geophysical logs.”
“Describes a search for geological evidence of meteorite impact structures in Britain. The statistics of impact structures indicate that Britain should have Phanerozoic impact structures up to tens of kilometres in diameter. A constant theme is the importance of atmospheric break-up of small asteroids and comets. These fragmenting bodies produce anomalously shallow craters with low rims and central peaks; three British structures of this type are identified. Analysis of fireball statistics implies that damaging fireball explosions occur over the British Isles on a time-scale of decades. On a time-scale of millennia, however, more damage is done by Atlantic impact tsunami.”
“Mackenzie prefaces his absorbing account of the new “giant impact” theory of the moon’s origin with the fascinating story of humanity’s long relationship with Earth’s only natural satellite. Evidence of that relationship begins with what is very probably a lunar calendar among the famous Lascaux cave paintings, and continues in early civilizations’ timekeeping uses of the moon and classical Greek ideas about the moon’s composition. In the fifth century B.C.E., Anaxagoras correctly realized that the moon was made of rock. Later, Aristotle didn’t agree, and his view held sway for centuries.”
“This volume is the 8th in a series of impact books resulting from the activities of the scientific program “Response of the Earth System to Impact Processes” (IMPACT), by the European Science Foundation. The book resulted from an international meeting at Mora, Sweden, which was held as part of the IMPACT program. The papers cover various structural geologic, geochemical, and geophysical topics on research of asteroid impact structures on Earth and Mars.”
“In recent years, meteorites have caught the imagination of scientist and collector alike. An army of people are now actively searching for them in the hot and cold deserts of Earth. Fascinating extraterrestrial rocks in meteorites are our only contact with materials from beyond the Earth-Moon system.”
“The Celtic myths, involving heroic warriors such as Finn and CuChulinn, can be read as simple primitive stories, but closer examination reveals strange descriptions and relationships.
The authors of this ground-breaking book argue that all the principal characters are aspects of the one Celtic sky god, Lugh, who was a comet. Against the background of a comet scenario this re-interpretation of about ten key Celtic myths shows how many of the descriptions in the myths fit the appearance of comets.
The fact that these comets on occasions produced abrupt environmental changes, that can be traced in the tree-ring and ice-core chronologies, pins the stories to a central reality. With a novel twist this original book confirms the widespread belief that these stories must contain a ‘core of truth’.”
“Could both Stonehenge and the pyramids of Egypt have been constructed to observe and commemorate a period of phenomenal meteor storms and asteroid detonations produced by a burst of activity in the Taurid Complex 4,500 to 5,000 years ago? Author Duncan Steel examines the evidence indicating rogue asteroids and doomsday comets may have been behind these and other ancient phenomena.”
“The End of the Dinosaurs gives a detailed account of the great mass extinction that rocked the Earth 65 million years ago, and focuses on the discovery of the culprit: the Chicxulub impact crater in Mexico. It recounts the birth of the cosmic hypothesis, the controversy that preceded its acceptance, the search for the crater, its discovery and ongoing exploration, and the effect of the giant impact on the biosphere. Other mass extinctions in the fossil record are reviewed, as is the threat of asteroids and comets to our planet today. The account of the impact and its aftermath is suitable for general readers. The description of the crater geology is in enough detail to interest students of the earth sciences. A detailed index and bibliography are included.”
“During its five billion year history, Earth has been hit countless times by asteroids and meteorites. Over 150 crater-producing events have been identified, and this book describes all 139 sites worldwide at which evidence of the impacts can be seen. They range in age from recent craters formed this century to the highly eroded billion-year old ancient craters. Some are spectacular to visit, such as the Barringer Crater in Arizona, the ring-shaped mountains of Gosses Bluff, Australia, and the huge crater at Ries in Germany.
For each site there is a summary table giving location, size, age and present condition. Maps are included where necessary. The author has visited many of the sites and his photographs enrich this thorough survey. Meteorite craters are fascinating to visit, so the descriptions include guidance about access and suggested itineraries for the large structures.”
“On the morning of June 30, 1908, a fireball cascaded down the Siberian sky and exploded with 2000 times the force of the nuclear blast that devastated Hiroshima, Japan. Weighing some 100,000 metric tons, the cosmic missile cut into the atmosphere and shattered in a rapid series of bursts, felling trees and incinerating an area of 2150 square miles – now known as the Tunguska ‘event’.
In the spring of 1992, Roy Gallant was invited by the Siberian branch of the National Academy of Sciences to take part in the annual Tunguska Expedition, to investigate this largest meteorite explosion in human history.”
“In the early years of the twentieth century, an enormous bowl-shaped hole in the high plains of northern Arizona was investigated by a mining engineer and his associates. The hole was almost three quarters of a mile wide-a little over one kilometer¹-and it penetrated thick layers of subsurface rock.
The investigators concluded that it was created thousands of years ago when a mass of meteoritic iron struck the earth, and they produced extensive evidence in support of their claim.”
“Norton (astronomy, Central Oregon Community College) tells the story of meteorites and our attempts to read their history. Topics include the development of the interdisciplinary science of meteoritics, asteroids, current classifications of meteorites, and the impact of the comet Shoemaker-Levy on Jupiter in 1994.
“A straightforward, thorough look at all aspects of meteors and meteorites, including how and where meteors originate, when and where to watch for them, and how to classify, collect, and preserve meteorites. Meteor showers, interesting meteorite craters, and tektites are all discussed in detail. Also contains a comprehensive listing of meteorite organisations, dealers, museums, and references.”
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