Science

Cosmic impact may have wiped out saber-tooth cats

By James Maynard , May 26, 2013 05:43 PM EDT
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Saber-tooth tigers, woolly mammoths, and many other ancient species may have been wiped out at the end of the last ice age, not by over-hunting, but by an impact from space.

Impact spherules found on four different continents suggest that a large celestial collided with the Earth, caused massive fires, and spread dust into the atmosphere that blocked out the Sun, causing the extinction of some of the best-known species from that distant epoch.

The Earth was warming up from the last ice age 12,800 years ago when the planet was hit by a large object from space, throwing tremendous quantities of dust and debris into the air. This cooled the Earth significantly, reversing the warming trend and bringing about the cooler period known as the Younger Dryas cool episode.

James Kennett, emeritus professor of earth sciences at UC Santa Barbara, believes that this dramatic cooling of the planet occurred in as little as one year.

The cause of the Younger Dryas cooling episode has been hotly debated for years by researchers. It was during this period that many species of animal, including the woolly mammoth, mastodon and saber-tooth tiger disappeared, along with the ancient Clovis People. Over-hunting by ancient people has often been blamed for these extinctions, but tiny pieces of rocks called impact spherules point to another conclusion - a colossal impact from space.

"This evidence continues to point to a major cosmic impact as the primary cause for the tragic loss of nearly all of the remarkable American large animals that had survived the stresses of many ice age periods only to be knocked out quite recently by this catastrophic event," Kennett said.

Researcers looked at the geological layer known as the Younger Dryas Boundary (YDB) on four continents and found not only these impact spherules, but also other evidence pointing to a colossal impact from space. These included fullerenes, nanodiamonds, and the tell-tale sign of a collision from space, iridium. Over 11 million tons of these glass spheres, many melted together, were spread over 20 million square miles in nine countries.

These distinctive spherules are created when super-hot melted glass is quickly cooled, often by being lifted high into the atmosphere. Such formations can also be produced by the action of volcanoes or lightning strikes. Kennett studied the spheres carefully under an electron microscope to confirm the cause of their formation.

"Because requisite formation temperatures for the impact spherules are greater than [4,000 degrees Fahrenheit], this finding precludes all but a high temperature cosmic impact event as a natural formation mechanism for melted silica and other minerals," Kennett said.

Assisted by colleagues from two dozen organizations, Kennett studied over 700 samples samples collected from 18 different locations.

The impact would not only have kicked up dust on its own, but could have also sparked wildfires that spread over entire continents, further blocking the Sun, leading to starvation worldwide. A layer of carbon called a black mat, likely caused by the massive fires, lies just above the impact layer. North America saw the loss of its own varieties of camel and horse during this cooling period.

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