Oldest microfossils suggest life thrived on Earth about 4 billion years ago

Ancient microbes were spewed from deep-sea hydrothermal vents, study claims

hematite

SIGNS OF LIFE  In rocks left over from ancient hydrothermal vents, these microscopic tubes of hematite, an ore of iron, may be remnants of early microbes.

M. Dodd

Tiny, iron-rich fossils exhumed from the depths of an ancient ocean could reveal the cradle of life.