Where did it start? How did it grow complex? Why did it get big? Three moments in Earth’s early history when evolution suddenly, inexplicably turned up the dial.

© Photoillustration by Will Warasila for The New York Times

Where did it start? How did it grow complex? Why did it get big? Three moments in Earth’s early history when evolution suddenly, inexplicably turned up the dial.

© Photoillustration by Will Warasila for The New York Times