Geologic Time Basics

Earth’s history is huge! In order to understand earth’s history, humans must think in much larger units of time than those we use in our daily lives. Millions & Billions of Years!

Therefore scientists broke all those events from all those years into categories. Earth’s history is huge!

Measured in billions of years Time Eras periods epochs Measured in hundreds of millions of years Measured in tens of millions of years Measured in millions of years

Precambrian Time Largest chunk of earth’s history Began 4.6 billion years ago Ended 544 million years ago

1 st MAJOR Mass Extinction Towards the end of Precambrian Time (about 650 million years ago) massive climate change, “Snowball Earth” Theory As much as 70% of life forms went extinct.

There are 3 ERAS in Geologic Time The last 544 million years are broken into ERAS!

The First Era Paleozoic Era ( Pay-Lee-O-ZO-ic) “Age of Fishes”

Paleozoic Era Divided into 6 periods: Cambrian Ordovician Silurian MississippianPennsylvanian Devonian Carboniferous Permian Carboniferous Period divided into 2 epochs:

2 nd MAJOR Mass Extinction At the end of the Paleozoic Era, Pangaea formed, massive climate change. As much as 95% of life in Earth’s oceans went extinct. The worst extinction event in earth’s history

“Age of Reptiles” Stegosaurus T-Rex The second Era Mesozoic Era “Age of Reptiles” (Mess-O-ZO-ic)

Mesozoic Era Divided into 3 periods: Triassic Jurassic Cretaceous

3 rd MAJOR Mass Extinction Mesozoic Era ends with another mass extinction due to climate change. Scientists hypothesize that this extinction occurred because of an asteroid that struck the Earth along with volcanic events. 85% of all species disappeared, making it the second largest mass extinction event in earth’s history

Cenozoic Era “Age of Mammals” The Third Era Current Era (Sen-O-ZO-ic)

Cenozoic Era Divided into 2 periods: Tertiary Quaternary Each of these periods is divided into several smaller epochs