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October 4, 2013

PETERS: An explosion in the history of life

My brother likes to build buildings in his free time. He has a couple of timber-frame structures on his property that he put up over the years, and now he’s working on a more traditional “stick” building made of 2x6’s and 2x4’s. One thing all of his efforts have in common is that they begin as drawings and become blueprints. And even though he’s built with quite different approaches over the years, all his buildings have some things in common: windows, doors, and stairs to name just a few.

Many scientists would say that life on Earth also has a complex but single blueprint. Many animals are “bilaterally symmetric,” meaning they have left hand and right hand parts that are mirror images of each other. There are lots of other regularities, such as the fact that all mammals have backbones.

Some of the most interesting parts of life’s blueprint are the relationships that have predators feasting on their prey. The predator-prey relationship took time to become established Here’s the story:

Life has been around for about 4 billion years. At first life was mostly single-celled organisms living in the sea. Then a form of colonial algae turned up that, although simple by modern standards, may have had a lot to do with slowly producing oxygen for what had naturally been an oxygen-poor atmosphere.

As time went on some unique soft-bodied life forms appeared. It took a while for geologists and paleontologists to see them in the fossil record simply because they were small and didn’t have “hard parts” like shells that could clearly be preserved. Instead these animals looked something like worms or small fronds. A few of them made marks or impressions on the sediment of the seafloor and those impressions became preserved as a kind of subtle fossil. These animals, called the Ediacara fauna, were discovered in several places around the world once scientists knew what to look for. The Ediacara animals are long, like pencils, or flat, like pancakes. Most paleontologists think they had those body plans so that their skin could exchange gases with the water around them, meaning they didn’t need structures like gills or lungs.

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