Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New evidence says Earth’s greatest extinction caused by ancient meteorite

21.11.2003


Long before the dinosaurs ever lived, the planet experienced a mass extinction so severe it killed 90 percent of life on Earth, and researchers at the University of Rochester think they’ve identified the unlikely culprit.



"An ancient meteorite body, one from the days when the solar system was still forming, struck the Earth 251 million years ago," says Asish Basu, professor of earth sciences in today’s issue of Science. The research is the latest volley in a decades-long debate over what caused "The Great Dying," the greatest elimination of life in the planet’s history.

While scientists have been wrangling over whether a meteor caused this great extinction ever since a meteor was fingered with the blame for the later dinosaur extinction, these new findings add weight to the argument that a major meteorite did strike the Earth 251 million years ago, likely triggering climate change and unprecedented volcanic activity. That one-two punch so affected the composition of the atmosphere that it took thousands of years to recover--leaving only a relative handful of plants and animals alive.


Two decades ago, Nobel laureate Luis Alvarez and his son, Walter, detected huge concentrations of iridium throughout the world in rock dated to the end of the dinosaur era. Iridium is only found in such concentrations in asteroids, so they concluded that a giant asteroid had struck the Earth at that time, likely leading to the downfall of the dinosaurs. The Alvarez claims were at first largely dismissed, but the evidence grew and today it is accepted that their interpretation was largely correct.

Basu added weight to the Alvarez claims in 1988 when he announced the discovery of "shocked quartz"--special crystals that have split along certain planes indicative of a large impact--immediately beneath the Deccan Traps of India. The Deccan Traps are areas of huge volcanic deposits that have been dated to 65 million years ago, the time of the dinosaur extinction, so finding shocked quartz immediately beneath them suggests that a giant impact preceded these giant lava flows.

While a meteorite has been largely accepted as the source of the dinosaurs’ demise, the root of The Great Dying has been a mystery. In 1991, however, Basu published a study in Science that showed a massive and ancient lava flow in Siberia dated precisely to that greatest of extinctions 251 million years ago. The lava did not shoot out of the Earth like a giant volcano, but oozed molten rock for thousands of years--so much lava, in fact, that if spread evenly, it would bury the surface of the Earth under 10 feet of magma.

Further testing by Basu and Robert Poreda, professor of earth and environmental sciences at the University, and also co-author of the current Science research, showed that both the Siberian and Indian lava had come from as deep as 1,800 miles beneath the surface. "These were not just examples of local magma bubbling through the crust," explains Poreda. "Something brought this lava all the way up from near the Earth’s core."

To find what might have caused the Siberian flows meant finding rock samples 251 million years old--not an easy prospect since oceanic tectonic plates that make up 70 percent of the Earth’s surface are younger than that. Oceanic plates slide underneath continental plates as they move, thus carrying any evidence far beyond the reach of humans. From an area in Antarctica called Graphite Peak, Basu and Poreda took rock from a stratum that sat between a layer that contained many fossils and a layer nearly devoid of fossils called the Permian/Triassic, or P/T boundary. One of the fossils that had gone from prominence to sudden disappearance was Glossopteris flora, a plant that was widely known to have been wiped out in The Great Dying. This reassured the team that they had the right rock from the right period. Previous tests by Poreda on this same layer found shocked quartz and fullerenes, cage-like molecules, containing atoms of extraterrestrial gases, which again hinted at a meteorite or comet strike. These results, however, were disputed by some researchers.

Coming at the problem from another angle, Basu and Poreda separated out the magnetic particles from the samples from Graphite Peak and from a source of P/T strata in Meishan, China, and Japan. To their surprise they found that the grains that sorted out contained an iron alloy that does not occur on Earth. Some 40 pieces were tiny fragments of meteorite 4.56 billion years old, while other grains displayed metallic characteristics that were more indicative of being formed by extreme heat, such as that in a severe meteorite impact. The very fact that these grains had not deteriorated from weathering means they must have been buried quickly under sedimentary deposits, again, indicative of a major impact.

"At the end of the Permian era, Antarctica was close to its present position as the southernmost part of the ancient supercontinent, Pangea, while south China was at the equator and Japan was to the north of the equator," explains Basu. "Such a wide, global distribution of these metal grains in the P/T boundary strongly suggests that these grains mark a major impact of a celestial body at that time." Critics of the P/T impact theory may point to the lack of iridium, the element that is so rare on Earth but common in asteroids and which alerted Alvarez to the possibility of a meteorite as the death knell for the dinosaurs. The Rochester team’s work shows strong evidence that not all collisions with extraterrestrial bodies will leave an iridium footprint. Basu suggests that a collision with a comet, which may have a meteoric core, would be low in iridium. Thus the culprit that wiped out nine of every 10 creatures on the Earth and nearly ended life when it was just taking hold may have been created before the Earth itself was fully formed.

Basu and Poreda plan to continue searching for evidence of a catastrophic impact in the P/T layer in different sites around the world. They hope that if enough samples from enough locations show evidence of a major impact, then scientists will be able to construct the exact scenarios of how the two largest mass extinctions in history were caused by meteorite collisions.

Along with Basu and Poreda, the co-authors of the paper are Michail I. Petaev and Stein B. Jacobsen of Harvard University, and Luann Becker of the University of California, Santa Barbara.

Jonathan Sherwood | EurekAlert!
Further information:
http://www.rochester.edu/

More articles from Earth Sciences:

nachricht Predicting unpredictability: Information theory offers new way to read ice cores
07.12.2016 | Santa Fe Institute

nachricht Sea ice hit record lows in November
07.12.2016 | University of Colorado at Boulder

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Electron highway inside crystal

Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.

Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Researchers identify potentially druggable mutant p53 proteins that promote cancer growth

09.12.2016 | Life Sciences

Scientists produce a new roadmap for guiding development & conservation in the Amazon

09.12.2016 | Ecology, The Environment and Conservation

Satellites, airport visibility readings shed light on troops' exposure to air pollution

09.12.2016 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>