About 1.2 billion years ago, eukaryotic and multicelled organisms evolved because

oxygen became available from cyanobacteria

banded iron formations developed

meteorite impacts increased

the atmosphere got thicker from volcanic outgassing

The correct answer for the question that is being presented above is this one: "oxygen became available from cyanobacteria." About 1.2 billion years ago, eukaryotic and multicelled organisms evolved because oxygen became available from cyanobacteria.

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