Geologic Time Scales

Time Periods In Evolution

Millions of years ago (mya)

Major Events in the History of Life on Earth

Millions of years ago (mya)

Precambrian

4,600-544

Hadean Eon

4,600-3,800

The Earth formed as a solid planet

4,600

Cryptozoic Eon

3,800-544

Formation of atmosphere and oceans

3,800

Archaean Era

3,800-2,500

Life (the first bacteria) formed

3,500

Proterozoic Era

2,500-544

Oxygen began to build up in atmosphere

2,500

650-544

First cell with a nucleus (called "eukaryotes")

1,400

Phanerozoic Eon

544-Today

First organism with many cells (= multicellular algae)

1,000

Paleozoic Era

544-245

First soft-bodied animals (like jellyfish and simple worms)

680

544-505

First animals with hard shells

(= marine invertebrates)

540

505-440

First animal with a backbone, vertebrates (= a jawless fish)

510

440-410

First land plants, (like ferns, NOT flowering plants!)

440

410-360

First land animals (= insects)

400

360-286

First amphibians, (like frogs)

360

360-325

First reptiles, (like lizards)

300

325-286

First dinosaurs

235

286-245

Mesozoic Era

245 to 65

248-213

First mammals, (small rat-like insect-eaters)

225

213-144

First birds

150

144-65

First flowering plants

140

Cenozoic Era

65-Today

65-1.8

Mass extinction of many kinds of life, including dinosaurs

65

65-55

First primates (similar to tree shrews)

65

55-40

Primative Apes appear, Elephant, horse, and camel develop.

40

40-26

First monkeys

35

26-14

Grasslands spread

26

14-1.75

Modern sea life appear.

14

1.8-Today

The beginning of human-like animals (hominids)

4

1.75-0.025

The Ice Ages being, mammals dominate Earth

1.75

0.025-Today

Modern humans (Homo sapiens sapiens)

0.05