Geologists Discover New Way of Estimating Size and Frequency of Meteorite Impacts

Apr 12, 2008
Geologists Discover New Way of Estimating Size and Frequency of Meteorite Impacts
Geologists have discovered a new way of estimating the size of impacts from meteorites. Credit: NASA

Scientists 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."

Source: National Science Foundation

Explore further: Lava slows but still on track to hit Hawaii market

add to favorites email to friend print save as pdf

Related Stories

Half-baked asteroids have Earth-like crust

Jan 07, 2009

Asteroids are hunks of rock that orbit in the outer reaches of space, and scientists have generally assumed that their small size limited the types of rock that could form in their crusts. But two newly discovered ...

Recommended for you

Scientists make strides in tsunami warning since 2004

6 hours ago

The 2004 tsunami led to greater global cooperation and improved techniques for detecting waves that could reach faraway shores, even though scientists still cannot predict when an earthquake will strike.

Trade winds ventilate the tropical oceans

6 hours ago

Long-term observations indicate that the oxygen minimum zones in the tropical oceans have expanded in recent decades. The reason is still unknown. Now scientists at the GEOMAR Helmholtz Centre for Ocean Research ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Enthalpy
not rated yet Apr 13, 2008
Really ? "The meteorite was the trigger, scientists believe, for the mass extinction of dinosaurs".

Newspapers have less room for doubt than scientists have...

The Chixulub impact is just one possible explanation among others, and it has some drawbacks.

But it is so pittoresque that newspapers just can't resist it.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.