The Great Dying

6/18/06 – 6/24/06

by C. Zaitz

Some scientists would rather look down at the ground rather than up at the sky. I’ve never been one to dwell among the dust and rocks, but lately I’ve grown an appreciation for the science of dirt. Here’s why.

Sometimes the sky comes down to earth. A crater found near the Yucatan Peninsula of Mexico indicates that a 6 mile wide asteroid or comet hit the earth about 65 million years ago, and not long after, lots of plants and animals died. This was the K-T extinction (Cretaceous (K) and Tertiary (T) periods of geologic history), where about 75% of the world’s species were snuffed out, including the poster-critters of the time, the Dinosaurs.

But there was an even worse extinction in the distant past. About 250 million years ago, nearly 90% of all life on earth was extinguished by some mechanism. The so-called “Great Dying” is also known as the Permian -Triassic (P -T) extinction. When 90% of all life on earth dies, scientists want to know why. Until now, there was no smoking gun, other than the usual suspects of volcanism, plate tectonics, changing climate, etc.

The latest news in “astro-geology” is that the location of the impact of a giant asteroid has just been found. Now we see the smoking gun, and it looks like the bullet was about 30 miles wide! Unfortunately the gun isn’t really smoking anymore- it has had 250 million years to cool. The crater left by the impact is hard to see. Over hundreds of millions of years, the ocean floor has subducted (slid underneath a continent). New ocean floor is created by the upwelling of lava. Therefore, not much of the original impact is left. A 300 mile wide land mass was discovered in East Antarctica by measuring the difference in gravity from one spot to another. Scientists overlaid radar maps of the area and the huge land mass fit inside a circular ridge. There are other suspects, however; massive volcanic eruptions also took place around the P-T boundary. But now geologists can compare and contrast these major extinctions and the factors that may have caused them. It’s pretty safe to say that when giant rocks fall from the sky, things go badly here on earth.

In July I will be heading west to study geology with a small group of college students. We will drive to Wisconsin, South Dakota, and Wyoming: The Badlands, The Black Hills, and Mt. Rushmore. I will be able to see the actual K-T boundary. It’s a visible line in the rocks. There is a high amount of the element iridium in this layer. High amounts of iridium indicate asteroid collision, since normal rocks from earth don’t have as much. Finding high levels of iridium is another smoking gun in the killer-asteroid scenario, and makes a good case for finding ways to prevent space rocks from hitting the earth in the future.

Knowing that rock-scientists don’t have much time to look up, I have elected myself “official night sky guide.” I’m anticipating dark skies so I’m brushing up on the harder-to-find constellations. Maybe we’ll see some meteors. I’ve heard that when you’re out in the wilderness, you can almost hear them burn up. I hope they do burn up. I’ll dig into the earth to see the rocks from space, but I don’t want to be under one when it hits!

Until next week, my friends, enjoy the view!