If you could travel 600 million years back in time, you would not see one animal on Earth. In fact, you would be the only creature bigger than the head of a pin. Although the Earth had existed for more than 4 billion years by that time, only the simplest, tiniest kinds of life had made it their home.
Then BAM!--animals appeared. Ancient relatives of nearly every species that has ever crawled, flown or walked showed up between 543 million and 510 million years ago. That time is called the Cambrian (Kam-bree-un) period. The Earth's animal population grew so suddenly and fast in this period that scientists call it "the Cambrian explosion."
Meet The Relatives!
It's hard to believe that the freaky Cambrian animals are the ancestors of modern species. Anomalocaris, (A-nom-uh-lo-care-is), had spiny arms to catch small animals. It would then crush them in its circular jaw, which snapped shut like a camera's shutter. Anomalocaris is believed to be an ancestor of crabs and spiders.
One puzzling creature had pointy spines that looked like legs. It took scientists years to figure out that they were looking at a fossil of Hallucigenia (Ha-loos-i-jen-i-a) upside down! The long, slender spines really jutted up from its back.
Dr. Seuss could have invented Opabinia (Oh-pah-bin-i-a), a five-eyed creature with a hoselike snout. Harvard paleontologist Stephen Jay Gould called the Cambrian animals "weird wonders." But where did they come from? Did a change in the Earth's climate make it possible for these animals to appear suddenly?
To answer these questions, researchers wanted to see fossils from just before the Cambrian, a time called the late Vendian period. Fossils of Cambrian animals have been around for nearly a century. But researchers wanted to find out what had happened just before the explosion of life. The problem was, late Vendian fossils were nowhere to be found. It was as if some pages were missing from life's history book.
An Explosion Of Research
Over the past few years, fossils from this mysterious period have been found in ancient rocks in Africa and Siberia. They help explain how the earliest
ancestors of today's animals came to be.
The fossils show that animals grew more complex in the Vendian period. They were also bigger than the earlier, microscopic animals. Some were wormlike. Some reached three feet across. Others had shells. They all floated or crawled in the sea.
Some researchers now believe that these changes were important steps on the road to the Cambrian explosion. Others think huge earthquakes, ice ages and other big changes in climate and atmosphere triggered the burst of new creatures.
How Fast Was The Explosion?
One of the biggest surprises to researchers looking at the Cambrian explosion is how quickly it happened. New ways of measuring the age of fossils show that the animal explosion happened within a period of 5 million to 10 million years.
Most experts thought it took hundreds of millions of years for new creatures to develop. That has been the view ever since Charles Darwin published his theory of evolution in 1859. His theory explains how animals and plants slowly change, or evolve, in order to survive.
Some scientists think there is another kind of evolution that happens in a geological flash. To find more evidence, they will keep studying the weird wonders of the Cambrian and the late-Vendian times. Says Guy Narbonne, a researcher at Queen's University in Ontario, Canada: "That's where all the action is."