Imagine that you built a time machine and successfully traveled 2 billion years back in time. What would you observe, given our current understanding of Earth's history?
A) dinosaurs roaming Earth
B) forests and insects everywhere on Earth
C) the ongoing heavy bombardment of Earth
D) a severe scarcity of oxygen in the atmosphere
E) You would be floating in space because Earth hadn't formed yet.

Question

Quizplus · Accepted Answer

2 billion years ago, Earth's atmosphere had very low oxygen levels, as the Great Oxidation Event had only recently begun to increase atmospheric oxygen.

Imagine That You Built a Time Machine and Successfully Traveled