Precambrian time covers the vast bulk of the ... The cnidarians, which included sea anemones, corals, and jellyfish, had sac-like bodies and a simple digestive system with a mouth but no anus.

As underwater chimneys called deep-sea vents release dissolved iron into Precambrian waters, oxygen is used up as quickly as it is produced. Once the iron supply is exhausted, however, oxygen ...

In a study published in Precambrian Research Monday by scientists ... global ocean to create a nutrient-rich shallow marine inland sea," Fru said in the press release. The researchers believe ...

The Precambrian eon is vast ... like that found today in hydrothermal vents along volcanic ridges in the deep sea -- probably supplied the energy.