(b) Stages on the geological time scale are represented as a spiral.The earliest life comprising Ediacaran biota was long believed to include only tiny, sessile, soft-bodied sea creatures.The largest genetic study ever performed to learn when land plants and fungi first appeared on the Earth has revealed a plausible biological cause for two major climate events: the Snowball Earth eras, when ice periodically covered the globe, and the era called the Cambrian Explosion, which produced the first fossils of almost all major categories of animals living today.According to the authors of the study, which will be published in the 10 August 2001 issue of the journal Science, plants paved the way for the evolution of land animals by simultaneously increasing the percentage of oxygen in the Earth's atmosphere and decreasing the percentage of carbon dioxide, a powerful greenhouse gas.
Fossils believed to represent the oldest animals with hard body parts were recently discovered in South Australia.
(a) Earth's history is divided into eons, eras, and periods.
The Ediacaran period was the final period of the Proterozoic Era which ended in the Cambrian period of the Phanerozoic Era.
The time before the Cambrian period is known as the Ediacaran period (between 635-543 million years ago), the final period of the late Proterozoic Neoproterozoic Era .
It is believed that early animal life, termed Ediacaran biota, evolved from protists at this time.