by James Robinson

Created on: February 08, 2009

There is a widely held belief that 65 million years ago a massive object crashed to earth from outer space, an event that resulted in the extinction of the dinosaurs, and most of the other life forms then existing at that ancient time.

Substantial geological evidence has been uncovered to show that such an impact occurred. A crater site has been identified in the Yucatan Peninsula in eastern Mexico, known as the Chicxulub Crater, and geologists who are in agreement with the impact theory are satisfied the event that created Chicxulub is the culprit leading to the mass extinctions.

The impact theory was developed in the late1970's by geologist Walter Alvarez and his father, Luis Alvarez, a Nobel prize-winning scientist. It came after geological field-work done by Walter Alvarez in Gubbio, Italy, where he was investigating sedimentary deposits at the boundary layer between rocks dated to two geological periods, one of which was the period in which it was known that dinosaurs became extinct. There he discovered a thin band of a mineral identified as iridium, an element normally rare at the surface of the earth but known to be much more common in meteorites, solar system debris that has fallen to earth from outer space. After investigation, a similar iridium layer was found at many other locations around the world where rock types of the same geological periods existed.

From this it was hypothesized that the iridium was of extraterrestrial origin and had arrived on earth when a six mile sized asteroid crashed into the earth from space with earth shattering force and with the release of stupendous energy, ejecting matter up into the atmosphere to be borne around the globe by air currents and subsequently deposited at many far away locations.

From this assumption, scenarios were developed to describe what could have happened following the moment of impact that would then lead to the eventual extinctions of the dinosaurs and also of approximately 70% of all other life forms on land and in the seas. Thus the impact theory gained recognition.

This conclusion was immediately contested by scientists who believed the extinctions were caused instead by massive volcanic eruptions in India, known as the Deccan Traps, that took place during the age of the extinctions.

Dewey McLean of Virginia Tech was an early opponent who argued, in the face of much unpleasant resistance, that the dinosaur extinctions occurred during a Deccan Traps volcanism-induced greenhouse climate change. In

• 1
• 2
• 3
• Next Page >>