Scientists Use Primitive Site to Model Life's Beginnings

Oct. 18 -- For around 3 billion years, life on this planet consisted entirely of simple, single-celled organisms, and then quite suddenly something astonishing happened. Around 570 million years ago, mother Earth hosted an unparalleled explosion in life.

Multi-celled plants and animals began to appear and proliferate in a period that may have lasted only a few million years, laying the foundation for life as we know it today.

It is called the Cambrian Explosion by some, or the Cambrian Transition by others, but by whatever name it was surely the most important period in the biological history of the Earth.For years, scientists have been asking why the planet was biologically boring for so long, and why it changed so rapidly during that era.

“One of the big puzzles about the Cambrian Transition is why, for so long on Earth, there were just these microorganisms with no major grazers consuming them,” says biologist James Elser of Arizona State University in Tempe. When grazers finally appeared they came on with gusto.“What took them so long?” Elser asks.

Primitive But Contemporary Model

Theories abound, but it isn’t possible to go back to the Cambrian period and run experiments to see which ideas are most likely correct. Still, it turns out that nature may have provided another way.

In an isolated area of Mexico, about an eight-hour drive south of the U.S. border, scientists have found what they believe to be a modern analogue of the Cambrian era. A series of streams and ponds near the Mexican village of Cuatro Cienegas harbor a simple biological system that appears to have diversified dramatically in only 40,000 years. What really excites the scientists is the presence of living stromatolites, bacterial structures that look a lot like coral reefs that are formed by the life processes of cyanobacteria, also known as blue-green algae.

Prior to the Cambrian Explosion, stromatolites literally covered the Earth, and they are now the most abundant fossils on the planet, according to ASU paleontologist Jack Farmer, who has made them his personal passion. But with the emergence of grazing animals, the stromatolites began to disappear.