Eons, Eras, Periods, and Epochs of the Earth

Origin of Earth

Oldest known rocks on Earth's surface

Note: Answer should be "Between Eon and Eon"

Oldest fossils of cells (prokaryotes appear)

Concentration of atmospheric oxygen begins to increase

Oldest fossils of eukaryotic cells appear

Diverse algae and soft-bodied invertebrate animals appear (Answer as "Period-Eon")

Sudden increase in diversity of many animal phyla (Cambrian explosion)

Note: Your answer should be in the format "Period-Era-Eon"

Marine algae abundant; colonization of land by diverse fungi, plants, and animals.

Note: Your answer should be in the format "Period-Era-Eon"

Diversification of early vascular plants

Note: Your answer should be in the format "Period-Era-Eon"

Diversification of bony fishes, first tetrapods and insects appear.

Note: Your answer should be in the format "Period-Era-Eon"