[delta_p_delta_x]

The fossil record. There is little evidence of very complex animal life before about 541 million years ago, which is when the Cambrian explosion begun.

[no_wizard]

When you say very little, do you mean none, or there is some questionable evidence?

I'm genuinely curious

[dudinax]

Before "modern" life evolved in the pre-cambrian era, there was the Ediacaran life forms that were complex multicellular life, but died out millions of years before the Cambrian explosion.

https://en.wikipedia.org/wiki/Ediacaran_biota

[TheBlight]

Given the surface of the planet is such a dynamic environment, I wonder how much evidence we should expect even if it did exist.

See also: https://www.scientificamerican.com/article/could-an-industri...

[Rebelgecko]

There's quite a few fossils showing single-celled organisms from 3+ billion years ago. I imagine if more complex life existed the fossils could've survived