Time

Years ago

Billions of

years ago (bya)

Event

4,600,000,000

4.6

Origin of the Earth

3,800,000,000

3.8

First cells (no nucleus) appear

3,700,000,000

3.7

Period of no free oxygen

2,200,000,000

2.2

Cyanobacteria (no nucleus)

produce oxygen (a poison)

2,000,000,000

2.0

Oxygen accumulates in the

atmosphere; cells evolve to use it

1,400,000,000

1.4

Complex cells (with a nucleus) appear

1,000,000,000

1.0

Advanced, more complex cells

(with a nucleus) appear

700,000,000

0.7

Multicellular plants and animals

600,000,000

0.6

Marine invertebrates abundant

500,000,000

0.5

Earliest fish appear

380,000,000

0.380

Oxygen attains 20% level (current

360,000,000

0.360

First amphibians appear

350,000,000

0.350

Trees appear

300,000,000

0.300

First reptiles appear

235,000,000

0.235

First dinosaurs appear

220,000,000

0.220

First mammals appear

40,000,000

0.040

Flowering plants appear

65,000,000

0.065

Extinction of dinosaurs, birds appear

3,000,000

0.003

Human-like forms appear

50,000

0.00005

Homo sapiens (humans) appear