During which era was the earth dominated by mostly single-celled organisms?

The first known single-celled organisms appeared on Earth about 3.5 billion years ago, roughly a billion years after Earth formed. More complex forms of life took longer to evolve, with the first multicellular animals not appearing until about 600 million years ago.

I think it’s Proterozoic era where life on Earth was mostly single-celled and small.

the answer is: metamorphic rocks often show the presence of fossils, also a

hope i

-lavira: )