Earth's Timeline and Eons

Question 1

Q: When did Earth form?

Answer 1

A: ~4.6 billion years ago.

Question 2

Q: What were the key events during the Hadean Eon (4.6–4 billion years ago)?

Answer 2

A:

Formation of the moon.
Meteorite bombardment and molten surface.
Formation of early oceans.

Question 3

Q: What began during the Archean Eon (4–2.5 billion years ago)?

Answer 3

A:

Oldest fossils of single-celled organisms appeared.
Photosynthesis evolved, increasing atmospheric oxygen.

Question 4

Q: What marked the Proterozoic Eon (2.5 billion–541 million years ago)?

Answer 4

A:

First multicellular organisms appeared (~1.7 billion years ago).
Oxygenated atmosphere.
Ediacaran Period (~630 million years ago): First large multicellular organisms.