500 million years ago
Some 500 million years ago animals developed hard parts from deposits of cellular waste. Unaware of the global power they were generating, the new oxygen-using bacteira flourished in their local niches all over the planet for hundreds of millions of years. But eventually, as atmospheric oxygen levels rose toward 21 percent, perhaps 2.2 billion years ago, a new kind of cell came on the scene. This was the eukaryotic cell with its key feature, the nucleus and its important secondary characteristic, oxygen-using cell parts known as mitochondria. When eukaryotes live as single cells they are called protists. Amoebae and paramecia are examples of protists. But as primitive as these cells may seem, their basic cell structure is almost identical to that of the multicellular bodies of animals, fungi, and plants. As Stonehill College astronomer Chet Raymo pointed out, the difference between the new cells and the old bacteria in the fossil record looks as drastic as if the Wright Brothers' Kitty Hawk flying machine had been followed a week later by the Concorde jet. But this doesn't mean that something miraculous happened--divine intervention to get from bacteria to fungi! Rather, the genetic evidence is clear: the new cells, the kind that we find in human bodies (and, if you add the green parts called chloroplasts, in plant bodies) came about when different kinds of bacteria merged. In retrospect, this makes sense: the bacteria that were able to detoxify hazardous oxygen were in great demand, and any organism that could team up with them was assured life on the surface rather than death or slinking down into the relative safety of the anoxic muds! Learn More
© 2005 by Sciencewriters
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