where did they go











WHERE DID THEY GO?

BY

JOHN J. HATFIELD

EARTH SCIENCE LAB 2234

TERM 2
































INTRODUCTION

The biggest mystery surrounding the dinosaur is how did they die? For over 130 million years dinosaurs ruled the earth. Then 65 million years ago, at the end of the Cretaceous period, they died out.
Nobody can really say what actually eliminated the species, although everyone has their very own idea. Asteroid impact, atmospheric changes (hot to cold), catastrophic eruptions and astronomical events (supernovas etc.). Some have ventured that early mammal inhabitation slowly “pushed” the dinosaurs to extinction. The most favored theory in the scientific field is that of the meteor impact. As always though, knowing when is part of discovering how and why.

THE TIMING OF THINGS
One problem that confronted scientist was determining exactly when the Cretaceous era ended and the Tertiary began. This investigation led to other problems such as accurately dating the fossils that are discovered and how to correlate the different fossils and sediment found around the planet.
Dating rocks is a tricky business. Even with radioactive dating, there is still a significant margin of error, which can encompass hundreds of millennia. Igneous rocks are the only rocks that can be dated by this method since it works on the elements from which they are formed. Strata is much more difficult to date. Generally, strata are classified by fossils found in each layer. With the assumption that species evolved and then spread rapidly (in geologic terms) it is possible for us to match and therefore date the same species and their containing deposits around the world.
In the 1970’s a significant breakthrough came when scientists discovered that the magnetic fields of various rock layers could give a guide to their age. The magnetic polarity of the Earth goes through periodic reversals. These changes are recorded in the layers of rock that are laid down at the time. By testing sediment and recording whether it was deposited under conditions of normal polarity and then measuring successive layers, we can build a time chart. By matching different charts from different areas with similar fossils, a more global correlation can be made.
These techniques led to the discovery of the boundary between the two eras. A single thin layer of clay found within predominantly limestone rocks established this. By comparing the marine life found in, above, and below the clay, the marine life, like the dinosaurs, had been terribly affected by the extinction event. The percentage of life in the upper layers was dramatically lower than that in the lower. This was far more compelling than what was suggested by dinosaur’s fossils.
Other samples of the clay were taken to laboratories to be analyzed. Part of the results showed a large concentration of platinum and iridium. These elements are very rare on the surface of the earth at the moment but they are present in meteoric dust that rains down from space at a known rate. That rate allowed for a measurement of how long it took for the clay to form.
Surprisingly, the clay held almost 30 times more iridium than the limestone layers above and below the clay. Similar layers in other parts of the world gave the same results. The conclusion was that a giant meteorite hit the Earth 65 million years ago and had released a large amount of the elements into the atmosphere. This was then dispersed throughout the atmosphere and fell to the Earth as sediment.
A connection was made between the meteor impact and the extinction of the dinosaurs and other species on Earth. The layers evidence showed that all life on the planet was influenced to some degree.
IMPACT

This evidence helped established the boundary between the Crustaceous and the Tertiary. Referred to as the K/T Extinction event. (K stands for Crustaceous and T stands for Tertiary.) Now this leads us to search for evidence of impact.
While scientists agree that some type of impact on the Earth around 65 million years ago, and the K/T boundary marks it. For quite a bit of time, it was hard to see where such an impact could take place. There had to be some sort of evidence scarring the face of the Earth if had such a terrible effect.
In the 1990’s a possible candidate for supporting evidence emerged. The Chicxulub crater in