Dinosaurs and Iridium

Dinosaurs were probably the most impressive beasts to ever walk on the face of the earth or swim its oceans. Part of our fascination with dinosaurs is the result of their large size and sometimes bizarre appearances, but part of our continuing interest revolves around why the dinosaurs disappeared. The theories to explain their extinction have ranged from the silly, such as small, crafty mammals chomping down the dinosaurs' eggs, or racial senescence, to more practical ones such as a tilt in the earth's orbit or radiation from a nearby nova. Even these more sane theories had a number of holes in them.

It was the discovery of a layer of iridium in the region around the Yucatan Peninsula that led to the Alvarez hypothesis. Further research found this iridium layer occurred worldwide, not just in Mexico. This hypothesis revolves around the speculation that a very large asteroid or meteorite, up to 10 km in diameter, slammed into the earth approximately 60 million years ago. Because so many meteorites and asteroids contain relatively high proportions of iridium, a layer of clay-containing iridium has led some scientists to believe that this impact was responsible for the extinction of the dinosaurs and so many other life forms. Actually, about half of all animal and plant species on earth went extinct at this time.

According to one theory, an enormous dust cloud was raised, which fell back to earth almost immediately. As the dust particles passed through the atmosphere, they heated up and raised the temperature on the earth's surface high enough to cause heat exhaustion in any animal too large to hide. The dinosaurs would have been unable to seek shelter in underground crannies or burrows and would succumb within hours to the intense heat. The atmospheric temperature would have been hot enough to set forests and grasslands afire. Small glass pellets have been found worldwide to support this theory.

Another theory agrees that there was a dust cloud, but in this case it caused a blocking of the sun that persisted for years, which caused photosynthesis to nearly cease. Deprived of the vegetation they need for survival, the plant eating dinosaurs would be the first to die, followed by the large meat eaters. Allegedly, the smaller mammals would be able to exist on much less food and be able to scrape by. Regardless of which theory sounds plausible to you, there is no disputing that the layer of iridium found all over the world has certainly given all of us something interesting to think about, and perhaps is a clue to the extinction of the dinosaurs.