Реферат: Dinosaurs Where Did They Go Essay Research

Dinosaurs: Where Did They Go? Essay, Research Paper

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 the Yucatan peninsula came into the spotlight. The crater is enormous. The crater itself and the rings of material that the impact produced stretch roughly 106-186 miles (170-300 km) across. The hardened molten rock from the impact proved to be the key to time. Remember, only igneous rocks can be properly dated by radioactive measurement. This allowed for the material in the crater to be dated at 64-65 million years old.

All of this seems to link everything together, details and the known dates. But how did an impact of this sort selectively kill off species? The answer could possibly be that the extinction was gradual, with only rarer and weaker creatures and organisms fading out in the long run. A lot of the marine life came to extinction due to acceleration by oceanic changes rather than directly caused by impact.

Why did some species become extinct and some others did not? There is no cemetery for us to examine at the boundary, so comparing evidence from the two eras? is problematic. Possibly, life forms that were already in decline became extinct. On the other hand, organisms that were on the brink of major expansion also disappeared from the planet.

CONCLUSION

There always will be argument over exactly what caused the extinction of the dinosaurs and other species. Most evidence does put the meteor impact at the root of the event. Unless technology improves or concrete evidence comes forward, we will stilled be mired in the chaos of personal belief and preference.

1. TITLE: THE GREAT DYING, COSMIC CATASTROPHE, DINOSAURS, AND THE THEORY OF EVOLUTION AUTHOR: KENNETH J. HSU 1986

2. TITLE: COSMIC IMPACT AUTHOR: JOHN K. DAVIES 1986

3. TITLE: THE DINOSAUR HERESIES, NEW THEORIES UNLOCKING THE MYSTERY OF THE DINOSAURS AND THEIR EXTINCTION AUTHOR: ROBERT T. BAKKER, Ph.D. 1986

4. TITLE: DYNAMICS OF DINOSAURS $ OTHER EXTINCT GIANTS AUTHOR: R. McNEILL ALEXANDER 1989

5. TITLE: THE DINOSAURS LAST GASP AUTHOR: JOHN MONCZUNSKI INTERNET RESOURCE: HTTP://WWW.GEOCITIES.COM/RAINFOREST/5707/DINO1.HTM

REPRINTIED: 1993/1994

6. TITLE: THE ASTEROID IMPACT VERSUS THE VOLCANO-GREENHOUSE DINOSAUR EXTINCTION DEBATE AUTHOR: DEWEY MCLEAN INTERNET RESOURCE: HTTP://FILEBOX.VT.EDU/ARTSCI/GEOLOGY/MCLEAN/DINOSAUR_VOLCANO_EXTINCTION/ 1994