"fried egg" looking things, to more plantlike organisms. An interesting exception is
the Tribrachidium, a tri-symmetrical organism (note that there aren’t any tri-
symmetrical organisms around today).
The Ediacarans
The Ediacarans were the precursors to the Cambrian Explosion, which later led to all the main lines of animal types today. The Ediacarans lived some 565 million to 543 million years ago (right up to the beginning of the Cambrian era), yet were first discovered only 50 years ago and were named after the Australian mining area where they were first found. Most scientists agree that the Ediacarans were the first multicelled animals to exist, a sort of experiment by nature (the first of many) to see what sort of new life could be cooked up after four billion years of algae, bacteria, and other one- celled organisms. Then, 565 million years ago, something happened; the one-cells became many cells, and spawned the bizarre shapes of the Ediacaran age.
About the Ediacarans
The first Ediacaran was discovered in 1946 when the Australian fossil hunter Reginald
Sprigg discovered a saucer-sized fossil in the hills around Ediacara, and labeled it as
an early jellyfish. Funny thing, all of the organisms of the Ediacaran time period were
like that; simple blobs, no bones. In fact, you can pretty much compare them to jellyfish
or annelid worms. At any rate, they weren’t discovered for quite some time since they
had no bones to be fossilized. Instead, they were trapped underneath a huge undersea
landslide that had a very low oxygen content (which promotes decay), and were thus
preserved. Of the fossils that have been found, Ediacarans range from huge blobs, to
"fried egg" looking things, to more plantlike organisms. An interesting exception is
the Tribrachidium, a tri-symmetrical organism (note that there aren’t any tri-
symmetrical organisms around today).
Where did they all go? The issue is currently under debate by scientists, whether an extinction actually happened or not. Many believe that the Ediacaran fauna were the precursors to the Cambrian fauna, and simply evolved into the Cambrian organisms. Others believe that there actually was an extinction, and the Ediacarans have no relatives in the Cambrian. With this theory, the Cambrians evolved after the Ediacarans were all dead.
Scientists speculate that the animals that coexisted with the Ediacaran fauna basically were divided into two categories: the floaters and the burrowers. The burrowers were the ones that figured out some way to survive at the bottom of the deoxygenated ocean. They’re the ones that survived into the Cambrian. The floaters, the big flat organisms, weren’t so lucky. They got nailed by a force that killed most ocean life except the burrowers. So, we can speculate that life eventually came from the burrowers, who were probably symmetrical organisms. Harvard's Knoll believes that in several seperate instances, the world's oceans became stagnant pools with warmer water overlaying colder, deeper water. Factors such as a warming climate, poor ocean circulation and increased bacterial activity may have caused the build-up of toxic gases such as hydrogen sulfide and carbon dioxide, which are formed when bacteria decompose matter, to build up in the deep water. Knoll explained, "All you have to do is slow down the vertical mixing and deep water will go anoxic... When that happens, you can actually set a death trap." At some point, something caused the layers of water to turn over, releasing the toxic gases and killing off most of the marine life. The event that overturned the waters in still unknown, whether it was a volcanic eruption, an impact from a meteor, climatic change, or some other short-lived event, however, based on the analysis of carbon isotopes in the rocks, he believes that this was also the case with the mass extinction in the Permian period (the largest extinction in history), which killed off 95% of all marine life.