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The Geologic Time Scale - Cretaceous

ERA

PERIOD

AGE
(of start)

Cenozoic

Quaternary

1.6 my

Tertiary

65 my

Mesozoic

Cretaceous

140 my

Jurassic

205 my

Triassic

250 my

Paleozoic

Permian

290 my

Carboniferous

355 my

Devonian

410 my

Silurian

438 my

Ordovician

510 my

Cambrian

540 my

Cretaceous 140 - 65 million years ago

Life

Dominant life includes:
Dinosaurs, birds, gymnosperm and fern forests

Tyrannasaurus Rex is alive during this time.
First angiosperms (flowering plants)

Climate

At the beginning of the Cretaceous, the climate was cold with snow and ice at the poles. Later in the period it became warmer with polar ice melting.

Geology

The main rock types/ deposits in PA are clay and sand.

K-T Boundary Extinction Event

At the end of the Cretaceous (abbreviated as K) and at the beginning of the Tertiary (T) a meteor hit the Earth just off of the Yucatan Peninsula in Central America. All around the world Iridium, an element found mainly in space, is found in the rocks at this time period. It is believed that the impact of the meteor caused a massive dust cloud and disrupted life on Earth. This may have caused the dinosaurs to become extinct, although by fossils it looked like the dinosaurs may have been dying out for some other reason before the meteor hit. About 50% of species become extinct.

Jurassic
Tertiary
 
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