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A Scientific Explanation to the Demise of Dinosaurs

You may know that a meteoric collision likely led to the demise of dinosaurs, but did you know earth’s had at least five mass extinctions during its history?

Published March 1, 2003

By Jeffrey Penn
Academy Contributor

Image courtesy of Panupong via stock.adobe.com.

A growing body of evidence suggests that the history of life on earth has been significantly affected by the collision of comets, meteorites and asteroids, resulting in global catastrophe and mass extinctions.

“Prehistoric mass extinctions of life were much more affected by extraterrestrial events than had ever been thought,” Michael Rampino, PhD, of New York University and the NASA Goddard Institute for Space Studies, told a Nov. 4, 2002, gathering at The New York Academy of Sciences (the Academy). “Earth’s history has been marked by periodic mass extinctions of life.”

Although scientists who first theorized that explosive collisions had significantly altered life on earth were not always taken seriously, Rampino said the theory is now not only accepted, but is considered among the most exciting fields in the sciences. “Astronomers and paleontologists formerly didn’t have cause to engage in conversations,” he said. “Now they have come to understand that their worlds are intimately connected.”

Five Mass Extinctions

More than 99 percent of species that have ever lived on earth are now extinct, according to Rampino. Paleontologists have identified five major mass extinctions and 20 minor mass extinctions on the planet earth. “The largest mass extinction was approximately 250 million years ago,” he said, “when 95 percent of marine species were wiped out.”

A mass extinction about 65 million years ago has long been widely recognized by scientists, since it represents the time when dinosaurs became extinct. “Dinosaurs were successful for a period of nearly 135 million years and suddenly became extinct about 65 million years ago,” Rampino said. “As many as 50 theories have been offered to explain the extinction of the dinosaurs, but none of those theories was supported by physical evidence.”

In the past 20 years, however, physical evidence gathered from sites as far apart as Italy and Colorado revealed that a thin layer of clay separated the geological record into two distinct eras. Analysis of the clay revealed “elevated levels of the kind of metals that are rare in terrestrial settings, but abundant in asteroids and meteorites,” Rampino said. “A similar review of geological samples from more than 150 sites around the world revealed that there is a global layer of this clay.”

In addition, scientists discovered a “shock layer” of quartz crystals in the clay, indicating high-pressure shocks. “Meteorite craters are the only places on earth that show these quartz crystals,” Rampino said. Scientists also discovered tiny spheres of glass in the clay. They are thought to have formed by intense heat from the impact and then dispersed into the atmosphere, where they cooled into their spherical shapes and dropped back to the ground.

Where is the Crater?

Despite the mounting evidence that a meteoric collision had eliminated the dinosaurs, scientists initially could not identify any crater on the earth that would explain the mass extinctions. In 1990, however, the giant Chicxulub Crater – nearly 200 kilometers in diameter – was discovered buried in the shallow sea just off the coast of Mexico’s Yucatan Peninsula. Additional exploration in Mexico indicated a thick bed of course sand, likely washed to shore by a giant wave (tsunami), in the precise layer of the geological record thought to indicate the mass extinction 65 million years ago.

What happened when the meteor collided with the earth? According to Rampino, scientists have estimated the object was nearly 10 kilometers long, causing the crater nearly 200 kilometers in diameter.

Environmental Catastrophe

“Dust and shock material were thrown out of the impact site into the atmosphere, causing heat and fires all over the world,” Rampino said. “The impact would have a tremendous, catastrophic effect on the environment. A high level of dust and ash would have clouded the sky, leading to a cooling and darkening that may have prevented photosynthesis.”

The geologist said such an event could have resulted in an “impact winter” lasting six months or longer. “Such an abrupt impact would lead to nothing less than a world-ending destruction of life,” Rampino said. “Food chains in the ocean and on land were broken, and plants and animals died out.”

Whatever life survived the calamity would continue to evolve, but the earth would see major changes in the dominant forms of life that remained. “The impact would provide opportunities for survivors to expand into empty niches, so that they dominate the earth during the next geological period,” Rampino added.

Prior Mass Extinctions?

Now that scientific consensus has accepted an impact collision as the most likely explanation for the extinction of dinosaurs, geologists are trying to determine if such collisions can be linked to other major and minor mass extinctions identified in the geological record.

Scientists have identified approximately 150 large impact craters on the earth. A statistical analysis reveals that about every 100,000 years a 1-kilometer object collides with earth, creating a crater of about 20 kilometers in diameter. “Only about once every 100 million years is there an impact of the magnitude that is capable of causing the dust storms and global fires believed to have eliminated the dinosaurs,” Rampino said.

Final proof of a connection between the largest mass extinction on earth – about 200-250 million years ago – and an impact collision has yet to be found. Evidence of such a crater may have eroded, he said, or remain hidden, perhaps below deep ocean water.

Future Extinctions?

If past evidence is also prologue, an impact collision that might cause mass extinctions on earth is likely in the next 40 million years or so, Rampino pointed out. “Earth exists in a zone of many earth-crossing asteroids and comets,” he noted.

While such projections appear far removed from the present, Rampino left his audience with a sobering fact. Concerning the potentially dangerous approach of comets, asteroids and meteorites, he pointed out, “there are no stop signs in outer space.”

Also read: Prehistoric Sloth-Like Creatures May Have Roamed the US


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