The Cause of the Dinosaur Extinction
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...