|
Geologists Discover New Way of Estimating Size and Frequency of Meteorite Impacts
April 14, 2008Scientists have developed a new way of determining the size and frequency of meteorites that have collided with Earth.
Their work shows that the size of the meteorite that likely plummeted to Earth at the time of the Cretaceous-Tertiary (K-T) boundary 65 million years ago was four to six kilometers in diameter. The meteorite was the trigger, scientists believe, for the mass extinction of dinosaurs and other life forms.
François Paquay, a geologist at the University of Hawaii at Manoa (UHM), used variations (isotopes) of the rare element osmium in sediments at the ocean bottom to estimate the size of these meteorites. The results are published in this week's issue of the journal Science.
When meteorites collide with Earth, they carry a different osmium isotope ratio than the levels normally seen throughout the oceans.
"The vaporization of meteorites carries a pulse of this rare element into the area where they landed," says Rodey Batiza of the National Science Foundation (NSF)'s Division of Ocean Sciences, which funded the research along with NSF's Division of Earth Sciences. "The osmium mixes throughout the ocean quickly. Records of these impact-induced changes in ocean chemistry are then preserved in deep-sea sediments."
Paquay analyzed samples from two sites, Ocean Drilling Program (ODP) site 1219 (located in the Equatorial Pacific), and ODP site 1090 (located off of the tip of South Africa) and measured osmium isotope levels during the late Eocene period, a time during which large meteorite impacts are known to have occurred.
"The record in marine sediments allowed us to discover how osmium changes in the ocean during and after an impact," says Paquay.
The scientists expect that this new approach to estimating impact size will become an important complement to a more well-known method based on iridium.
Paquay, along with co-author Gregory Ravizza of UHM and collaborators Tarun Dalai from the Indian Institute of Technology and Bernhard Peucker-Ehrenbrink from the Woods Hole Oceanographic Institution, also used this method to make estimates of impact size at the K-T boundary.
Even though these method works well for the K-T impact, it would break down for an event larger than that: the meteorite contribution of osmium to the oceans would overwhelm existing levels of the element, researchers believe, making it impossible to sort out the osmium's origin.
Under the assumption that all the osmium carried by meteorites is dissolved in seawater, the geologists were able to use their method to estimate the size of the K-T meteorite as four to six kilometers in diameter.
The potential for recognizing previously unknown impacts is an important outcome of this research, the scientists say.
"We know there were two big impacts, and can now give an interpretation of how the oceans behaved during these impacts," says Paquay. "Now we can look at other impact events, both large and small."
The National Science Foundation (NSF)
When meteorites collide with Earth, they carry a different osmium isotope ratio than the levels normally seen throughout the oceans.
"The vaporization of meteorites carries a pulse of this rare element into the area where they landed," says Rodey Batiza of the National Science Foundation (NSF)'s Division of Ocean Sciences, which funded the research along with NSF's Division of Earth Sciences. "The osmium mixes throughout the ocean quickly. Records of these impact-induced changes in ocean chemistry are then preserved in deep-sea sediments."
Paquay analyzed samples from two sites, Ocean Drilling Program (ODP) site 1219 (located in the Equatorial Pacific), and ODP site 1090 (located off of the tip of South Africa) and measured osmium isotope levels during the late Eocene period, a time during which large meteorite impacts are known to have occurred.
"The record in marine sediments allowed us to discover how osmium changes in the ocean during and after an impact," says Paquay.
The scientists expect that this new approach to estimating impact size will become an important complement to a more well-known method based on iridium.
Paquay, along with co-author Gregory Ravizza of UHM and collaborators Tarun Dalai from the Indian Institute of Technology and Bernhard Peucker-Ehrenbrink from the Woods Hole Oceanographic Institution, also used this method to make estimates of impact size at the K-T boundary.
Even though these method works well for the K-T impact, it would break down for an event larger than that: the meteorite contribution of osmium to the oceans would overwhelm existing levels of the element, researchers believe, making it impossible to sort out the osmium's origin.
Under the assumption that all the osmium carried by meteorites is dissolved in seawater, the geologists were able to use their method to estimate the size of the K-T meteorite as four to six kilometers in diameter.
The potential for recognizing previously unknown impacts is an important outcome of this research, the scientists say.
"We know there were two big impacts, and can now give an interpretation of how the oceans behaved during these impacts," says Paquay. "Now we can look at other impact events, both large and small."
The National Science Foundation (NSF)
Meteorites News and Current Meteorites Events RSSDiscovery of the source of the most common meteorites
When observing with the GEMINI telescopes, two astronomers from Brazil and the United States discovered for the first time asteroids that are similar to "ordinary chondrites", the most common meteorites found on Earth. Until now, astronomers have failed to identify their asteroidal sources because of the various geologic processes that occur after the meteorites are ejected from their asteroidal parent body.
Laser fluorescence could find life on Mars
A team of scientists from the United States and the United Kingdom has developed a technique using ultraviolet light to identify organic matter in soils that they say could be used to document the existence of life on Mars.
Lavas from Hawaiian volcano contain fingerprint of planetary formation
Hikers visiting the Kilauea Iki crater in Hawaii today walk along a mostly flat surface of sparsely vegetated basalt. It looks like parking lot asphalt, but in November and December 1959, it emitted the orange glow of newly erupted lava.
Scientists confirm that parts of earliest genetic material may have come from the stars
Scientists have confirmed for the first time that an important component of early genetic material which has been found in meteorite fragments is extraterrestrial in origin, in a paper published on 15 June 2008.
Ancient mineral shows early Earth climate tough on continents
A new analysis of ancient minerals called zircons suggests that a harsh climate may have scoured and possibly even destroyed the surface of the Earth's earliest continents.
Simple membranes could have allowed nutrients to pass into primitive cells
When the first cells developed, how could they bring molecules from the environment into their living interior without the specialized structures found on the modern cell membrane?
FSU geochemist challenges key theory regarding Earth's formation
Working with colleagues from NASA, a Florida State University researcher has published a paper that calls into question three decades of conventional wisdom regarding some of the physical processes that helped shape the Earth as we know it today.
Refining the date of the K/T boundary and the dinosaur extinction
Scientists at the University of California, Berkeley, and the Berkeley Geochronology Center have pinpointed the date of the dinosaurs' extinction more precisely than ever thanks to refinements to a common technique for dating rocks and fossils.
Meteorites delivered the 'seeds' of Earth's left-hand life
Flash back three or four billion years - Earth is a hot, dry and lifeless place. All is still. Without warning, a meteor slams into the desert plains at over ten thousand miles per hour. With it, this violent collision may have planted the chemical seeds of life on Earth.
UMd-led team finds ancient asteroids formed at solar system's start
Using visible and infrared data collected from telescopes on Hawaii's Mauna Kea, a team of scientists, led by the University of Maryland's Jessica Sunshine, have identified three asteroids that appear to be among our Solar System's oldest objects.
More Meteorites News Articles
 | The Day of the Triffids (20th Century Rediscoveries) by John Wyndham |
 | Field Guide to Meteors and Meteorites (Patrick Moore's Practical Astronomy Series) by O. Richard Norton, Lawrence A. Chitwood |
 | Go Big or Go Home by Will Hobbs |
 | The Ice Limit by Douglas Preston, Lincoln Child |
 | Rocks from Space: Meteorites and Meteorite Hunters (Astronomy) (Astronomy) by O. Richard Norton |
 | The Time Travelers Academy by Reginald Williams |
 | Exploring the Geology of the Carolinas: A Field Guide to Favorite Places from Chimney Rock to Charleston by Kevin G. Stewart, Mary-Russell Roberson |
 | The Real Science Behind the X-Files: Microbes, Meteorites, and Mutants by Anne Simon |
 | Souvenirs from Space: The Oscar E. Monnig Meteorite Gallery by Judy Alter |
 | Call Me Ahnighito by Pam Conrad |
| © 2008 BrightSurf.com |