Planet Earth

Just One Bite and Life Took Off

How evolution arrived at the Cambrian Explosion.

By Laura WrightFeb 5, 2004 12:00 AM

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The Cambrian Explosion—a burst of evolutionary innovation when most of the modern animal types originated—may have begun with a single chomp, says paleontologist Charles Marshall of Harvard University. Before 540 million years ago, simple animals called Ediacarans roamed the oceans. These organisms, which had no jaws, claws, or teeth, changed little for millions of years. Then some early creature evolved the ability to eat its neighbor. Once that happened, Marshall theorizes, animals had to juggle the need for food with the need to not be something else’s food. In response, they evolved a wide variety of body plans: Each creature made trade-offs to strike a balance for survival by developing hard shells, sharp teeth, and so on.

Andy Ridgewell of the University of California at Riverside sees a different evolutionary innovation reshaping the Cambrian world. During the Ediacarans’ latter days, the first tiny organisms with calcified shells began to populate the oceans. Ridgewell and his colleagues suggest these planktonic critters altered the flux of carbon atoms between air, water, and land. By drawing carbon out of the water to make their shells, the organisms smoothed the carbon cycle, dampening Earth’s climate extremes and making the environment more hospitable to complex organisms.

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