Not So Drab After All
The term given to the first half of the Earth’s 4-billion-year history--the Azoic era--means lifeless. That hasn’t proved to be apt. Scientists have found fossil evidence of single-celled bacteria dating back more than 3 billion years.
Nevertheless, the Azoic until recent years was regarded as a rather dull era when ambiguous scraps and blobs of chemicals stewed until the advent of the Cambrian period 543 million years ago. The Cambrian, 35 million years long, has been described as an explosion of biological creativity in which virtually all of the body forms characteristic of modern animals developed.
In the mid-1990s, however, evidence from the emerging field of molecular genetics suggested that the Azoic period was not so uneventful after all. Studying DNA, the genetic code that tells organisms how to develop, scientists crawled down the evolutionary tree and found that the genes that govern complex organs existed over a billion years before the Cambrian “big bang.”
Last week, archeologists reported the first confirmation that at least one complex creature existed over a billion years ago. In soda-straw-size tunnels in central India, they found fossils of an earthworm that, like modern mollusks, used senses and instincts to mine bacterial colonies for food.
The new discoveries are leading some scientists to challenge the traditional theory that higher animals like humans owe their greatest debt to the Cambrian period, when competition between myriad creatures made body parts more elaborate. They point out that the organs really key to survival--like eyes and hearts--may well have been fashioned instead during Azoic times, when competition was virtually nonexistent. Then, organisms could experiment easily with bold new biological designs--failing and trying again and again. In contrast, during the Earth’s latter history, as Indiana University biologist Rudolf Raff points out, “competition is severe, so if you’re not good at making a living, you’re dead meat.”
So maybe traditional scientific wisdom has had it backward. The Earth’s last 2 billion years may have been a time of new riffs on old themes, an era when body parts were not so much invented as altered, much as Ford changes the wind scoops on its Mustang every few years. And the Earth’s much-dismissed first 2 billion years may have been a progressive, if plodding, time of discovery.
Of course, this is still all speculation, but Aesop’s turtle may have been onto something. Maybe evolution is like long-distance running and the winner is what’s slow and steady.
