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SPACE GEOSCIENCE ARTICLE

The threat of asteroids
by MIKE BALDWIN

06.08.01: The MAGS general membership program for June 8, 2001 was presented by Dr. Gerrit Vershuur, author of "Cosmic Catastrophies", "Hidden Attraction: The Mystery and History of Magnetism", and "Impact: The Threat of Comets and Asteroids". Here are my notes from that meeting.

From his book, "Cosmic Catastrophies", published in 1978, Dr. Vershuur posed the question: Was the Bronze Age wiped out by an asteroid?" He went on to then us that if a star exploded 50 light years away from Earth, all life on Earth would be sterilized.

Scientists on Earth did not take the threat of an asteroid collision with Earth seriously until 1994, when the Schumaker-Levi comet slammed into Jupiter. We watched as bruises larger than Earth scattered across the face of Jupiter.

There are several different objects that could strike Earth from space:
(1) Meteors--called shooting stars as you watch them enter the atmosphere.
(2) Fireballs--apple-sized meteorites.
(3) Bolides--grapefruit-sized meteorites.
(4) Meteorites--large objects.
(5) Comets--such as the Tunguska Comet which struck Earth in 1908.
(6) Asteroids--could strike any day now.
(7) Tektites--glassy obsidian-like objects. The ones Dr. Vershuur showed us were covered with pocks (small craters) and had smoth edges like glass.

Meteor showers repeat every year. The Leonid shower will be visible on 17 November 2001. The best time to view the shower will be around 2:00 a.m on November 18. At that time, you might be able to see tens of thousands of meteors every hour. The Leonids get their name from the fact that it looks like the radiate from Leo. So if you locate Leo in the night sky, the meteors will be visible from that point.

Our planets and moons are covered with craters. Where did these craters come from? They came from impacts. Why don't we have craters on Earth. The fact is . . . we do. They could be found beneath the oceans, in highly forested areas, or in the mountains and deserts. The plate techtonics of Earth constantly change the face of the Earth. Any impact craters on Earth would eventually be destroyed by this plate movement. The atmosphere of Earth allows most potential impact objects to burn up before they reach the surface.

Recently, scientists have found the presence of iridium at the 65-million-year-old layer of strata in Italy. Iridium can only be found in extraterrestrial objects, therefore this iridium could have been the result of an asteroid collision 65 million years ago. Historians and scientists must work together to unlock the secrets of our past.

If a 6-mile-wide asteroids were to strike Earth, it would cause a 100-million megaton explosion and a 100-mile-wide crater. Such a crater exists beneath the waters of the Gulf of Mexico, off the coast of the Yucatan Peninsula.

Suppose that a 10km asteroid struck the Earth 65 million years ago. Here are the consequences:
(1) It would have passed through the atmosphere in less than one second.
(2) It would have punctured a hole in the atmosphere.
(3) The displaced air would have traveled sideways at the speed of a missle.
(4) A 200-mile-wide crater would have developed in just a few minutes.
(5) All that energy would have created fragmentation and shifting of rocks.
(6) A large percentage of those rocks would have become fireballs.
(7) Ejecta would have been raised several kilometers into the atmosphere.
(8) There would have been a shock wave more than a thousand kilometers away from the impact.
(9) Acid rain with the consistency and potency of battery acid would fall for weeks afterwards.
(10) The mantle on the other side of the Earth from the impact would bounce 60 feet.
(11) Burrowing creatures would have been the only survivors. They could live off the roots of dying and dead trees.
(12) Dinosaurs would have suffocated, or starved, or burned up.
(13) The temperature of the atmosphere would have risen to 2000 degrees F.
(14) All the forests would have burned up.
(15) There would have been no sunlight for a month!

Dr. Vershuur believes that is what happened to the dinosaurs of Earth . . . and that sounds like a pretty good theory to me!