Ediacaran

Ediacaran Fauna is a collective term for a variety of early organisms found in rocks older than the Cambrian Period that marked the beginning of life in classical paleontology. The name Ediacara comes from the Ediacara (Occasionally 'Ediacarian') Hills of South Australia where peculiar precambrian fossils were found by a geologist named Sprigg in 1946. Martin Glaessner initiated more serious study of these fossils in the 1950s. Glaessner initially thought the creatures to be primitive versions of animals such as corals, sea-pens and worms that were better known from later times. In subsequent decades, many more pre-Cambrian fossils have been found in South Australia. Additional fossils have been found in dozens of outcrops on all continents. Especially important deposits have been found in the White Sea area of Russia, in SouthWest Africa, in Northwest Canada, and in Newfoundland.

As time has passed, the Ediacaran faunas have, if anything, become more rather than less enigmatic. A few fossils such as Kimberella, Bomakellia, and Xenusion seem to be possible for precursors to Cambrian forms. Close to the Cambrian boundary, worm tracks, and various hard shelled forms - especially a collection of small forms known as the 'small shelly fauna' also appear to be probable precursors of Cambrian life. On the other hand, many of the best known Ediacaran creatures appear to be immobile blobs, disks, fronds, and air matress like shapes that have no obvious relationship to later forms. There is considerable controversy about the nature of many Ediacaran forms.

The Ediacaran faunas are sometimes referred to as "Vendian Faunas". Modern usage tends toward using "Ediacaran" to describe the full faunal range including algae, sponges, and all other life forms of the late preCambrian. The term "Vendian" is then reserved by some for a diverse collection of multilobed, softbodied, sessile forms that appear as fronds, disks, and other shapes. These are termed "Vendazoa" and have been proposed as a separate phylum or kingdom.

There are even older fossils known. Well dated fossils of bacteria are found in cherts as old as 3460 million years and probable bacterial mats known back to 3600 million years. 3800 million year old graphite in metasediments from Western Greenland is thought to be of organic origin. Many very old proposed fossils such as Eozoon have subsequently been rejected as naturally occurring pseudo-fossils. The oldest current candidates for early multicelled life are 2000 million year old tracks from West Texas, 1000 million year old tracks from India, and 700 million year old worm impressions from China.