Event

Time

“Lucy” (Australopithecus afarensis)

4     mya

Camel

35   mya

Grass

55   mya

Cenozoic Era begins

65   mya

Tyrannosaurus

65   mya

Ants

100 mya

First flowering plants

125 mya

Archaeopteryx

140 mya

Stegosaurus

160 mya

First mammal

240 mya

Mesozoic era begins

320 mya

Pangaea forms

260 mya

Earthworms

300 mya

Cockroaches

330 mya

Ferns

370 mya

Sharks

400 mya

Spiders

450 mya

Trilobites

520 mya

Jellyfish

545 mya

Paleozoic era begins

545 mya

Green algae

1     bya

Bacteria

3     bya

Precambrian era begins

4.6  bya

Figure 1. Events on the geological timeline

* Note (mya= million years ago, bya= billion years ago). These dates are approximations and will vary depending on sources consulted.