Geologic Time Scale

EON ERA PERIOD EPOCH MILLIONS
OF YRS
AGO
MAJOR BIOLOGICAL EVENTS
P
H
A
N
E
R
O
Z
O
I
C
C
E
N
O
Z
O
I
C
Quaternary Holocene

.01

Rise of civilization and agriculture. Extinction of large mammals in northern hemisphere.
Pleistocene 1.8 Modern humans appear. Four major glaciations cause rapid shifts in ecological communities.
Tertiary Neogene Pliocene 5 Extensive radiation of flowering plants and mammals. First hominids appear.
Miocene 23 Coevolution of insects and flowering plants. Dogs and bears appear.
Paleogene Oligocene 38 Worldwide tropical rainforests. Pigs, cats, and rhinos appear. Dominence of snails and bivalves in the oceans.
Eocene 54 Early mammals abundant. Rodents, primitive whales and grasses appear.
Paleocene 65 Early placental mammals appear; first primates; modern birds.
M
E
S
O
Z
O
I
C
Cretaceous   146 Marsupials, ants, bees, butterflies, flowering plants appear. Mass extinction of most large animals and many plants.
Jurassic   208 Dinosaurs and gymnosperms dominate the land; feathered dinosaurs and birds appear. Radiation of marine reptiles.
Triassic   245 Origin of mammals, dinosaurs and true flies. Less diverse marine fauna.
P
A
L
E
O
Z
O
I
C
Permian   286

Gymnosperms, amphibians dominant. Beetles, stoneflies appear. Major extinction of 95% of marine species and 50% of all animal families.

Carboniferous Pennsylvanian

325

First reptiles, cockroaches and mayflies appear. Extensive coal swamp forests. Sponge reefs.

Missippian 360 Echinoderms, bryozoans dominant in oceans. Early winged insects. First coal swamp forests.
Devonian   410 First amphibians. Extensive radiation of fish, land plants. Many corals, brachiopods and echinoderms.
Silurian   440

First spiders, scorpions, centipedes, early insects, vascular plants, jawed fish and large reefs appear.

Ordovician   505

First land plants, primitive fungi, sea weed appear. Diverse marine life: corals, molluscs, bivalves, echinoderms, etc.

Cambrian   543 Rise of all major animal groups. Metazoan life abundant; trilobites dominant. First fish. No known terrestrial life.

PROTEROZOIC EON

570 Origin of multicelled organisms. First sponges, colonial algae and soft-bodied invertebrates.
ARCHEAN EON 2,500

Oxygen levels rise as a result of photosynthetic organisms.
First eukaryotes (single-celled algae): 1.4 billion years old.
Earliest life, anaerobic prokaryotes (bacteria, archaeans) originate 3.5 billion years ago.

HADEAN EON 3,800-4,600 No life known. Cooling and solidifying of Earth's crust.