If we time-traveled back 1.8 billion years, the world would certainly not“seem the same”. The apex of life consisted of single-celled slime floating in ancient oceans.
The middle Pliocene is our closest analog to present-day greenhouse gas levels. It provides a probable peek into our future — several more degrees of global temperature rise and many meters of sea-level rise.
Oxygen was disappearing from the atmosphere for a billion years, Why?
The first ecosystems in geological history, wiped out by oxygen