1. Hadean eon --- a. formation of the solar system
2. Archean eon --- c. toxic atmosphere; first bacteria
3. Proterozoic eon ---- d. buildup of oxygen; first eukaryote
4. Phanerozoic eon. --- b. current eon
Explanation:
The Hadean Eon represents the formation of the planet that is time before the reliable fossilized record of the life and ended about 4.0 billion years ago. The Archean eon is characterized by the toxic atmosphere and the arrival of the first single-celled organism as bacterial life forms.
The current era dates to the geologic formation of the Phanerozoic eon and covers about 542 million years and the Proterozoic era was the formation of the first oxygen molecules and first Eukaryota.
