Geologic History Notes – Inorganic Changes Write everything in black font

The earth’s history is divided into 4 blocks of time called ERAS. -Except for the 1 st era, the Precambrian, each era is divided into smaller divisions called PERIODS.

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Eras are based on changes that occurred on the Earth. -Some of the changes were organic. -Some of the changes were inorganic.

Precambrian Era: -4.6bya (billion years ago) until 540mya (million years ago). -It was about 4 billion years long! That is about 88% of the entire geologic time scale.

The Earth formed: Molten at first Earth slowly cooled and the surface solidified into a crust with one supercontinent called Rodinia Original atmosphere had a lot of CO 2 and no oxygen Lots of meteor strikes Rain & oceans started There were some ice ages

Paleozoic Era: 540mya to 225mya. Earth cooled enough that volcanic activity calmed down to present levels The atmosphere is nearly the same as now 6 major continents (from break up of Rodinia) slowly form back into supercontinent Pangaea Remains of organism were fossilized

Mesozoic Era: 225mya to 65mya Pangaea broke apart into continents like today The Rocky Mountains formed The climate was hot and dry Magnetic pole reversals about every million years Huge asteroid strike 65mya

Cenozoic Era: 65mya to now Andes, Alps and Himalayan Mountains form Many ice ages occur Magnetic pole reversals about every 300,000 years (last one 780,000ya) The continents moved to present locations

How do we know about all this? Stratigraphy – the study of rock layers Law of Superposition – older rock layers are buried underneath younger rock layers Radioactive dating