Four Billion BCE: Battered Earth 

"No place on Earth was safe. Four billion years ago, during the Hadean eon, our Solar System was a dangerous shooting gallery of large and dangerous rocks and ice chunks."

(The gif below shows impacts over time: “Spatial distribution and sizes of craters formed on the early Earth. Each circle indicates the final estimated crater size; color coding indicates time of impact. Credit: Simone Marchi/SwRI.”)