Geologic Timeline

Precambrian

Jan 1, 1901

4.6 Billion - 544 Million Years ago
G - The Earth formed about 4.6 billion years ago.
B - Bacteria appeared about 3.5 billion years ago.

Precambrian Time

Period: Jan 1, 1901 to Dec 1, 1901

Cambrian

Jan 1, 1902

544 - 505 Million Years ago
G - Shallow seas cover much of the land.
B - Invertebrates with shells appear.

Paleozoic Era

Period: Jan 1, 1902 to Dec 1, 1907

Ordovician

Jan 1, 1903

505 - 438 Million Years ago
G - Warm, shallow seas cover much of Earth.
B - Invertebrates dominate the oceans.

Silurian

Jan 1, 1904

438 - 408 Million Years ago
G - Coral reefs develop.
B - Fish with jaws develop.

Devonian

Jan 1, 1905

408 - 360 Million Years ago
G - Seas rise and fall over what is now North America.
B - First amphibians reach land.

Carboniferous

Jan 1, 1906

Mississippian: 360 - 320 Million Years ago
Pennsylvania: 320 - 286 Million Years ago
G - Appalachian Mountains begin to form.
B - First true reptiles appear.

Permian

Jan 1, 1907

286 - 245 Million Years ago
G - Deserts become larger in tropical regions.
B - Reptiles become dominant on land.

Triassic

Jan 1, 1908

245 - 208 Million Years ago
G - Hot, dry conditions dominate the center of Pangaea.
B - First dinosaurs appear.

Mesozoic Era

Period: Jan 1, 1908 to Dec 1, 1910

Jurassic

Jan 1, 1909

208 - 144 Million Years ago
G - Pangea breaks apart as North America from Africe and South America.
B - First bird appears.

Cretaceous

Jan 1, 1910

144 - 66 Million Years ago
G - Widespread volcanic activity occurs.
B - First flowering plants appear.

Tertiary

Jan 1, 1911

66 - 1.8 Million Years ago
G - Continental glacier covers Antarctica.
B - First grasses appear.

Cenozoic Era

Period: Jan 1, 1911 to Dec 1, 1912

Quaternary

Jan 1, 1912

1.8 Million Years ago
G - Thick glaciers advance and retreat over much of North America and Europe, parts of South America and Asia, and all of Antarctica.
B - Mammals, flowering plants, and insects dominate land.