Unanswered questions about missing oxygen during the 1.4 billion years between the first hints of free oxygen and the Great Oxidation Event.
Banded iron formations are direct indicators of oceanic oxygen levels, and they provide us with a record of Earth’s oxygenation.
Life’s first challenge was achieving homeostasis by adapting to conditions in Earth’s oceans. Chemosynthetic bacteria were superbly suited to this task and they were probably the first cellular life forms, kicking off a grand evolutionary party.party.
Life spontaneously developed and given another water-rich solar system with a planet in the optimal temperature range for liquid water, we would expect it to happen again.