1. Earth History

2. Earth is 4.56 billion years old
Earth history is broken into different eons, eras, periods, and epochs based on geologic events and life.
We live in the Phanerozic eon, the Cenozoic era, the Quaternary period, and the Holocene epoch.

3. Precambrian
The Precambrian covers the majority of Earth’s history (~88% of earth’s history).
There are very few rocks found in this eon-these rocks are highly metamorphosed and located in areas called shields

4. Precambrian
Earth's early atmosphere was made up of water vapor, carbon dioxide, nitrogen, and trace gases.
Water was brought to Earth through meteorites-the condensing of water vapor led to oceans
Stromatolites (ancient algae) produced oxygen through photosynthesis, which created our oxygen rich atmosphere

5. Paleozoic The Paleozoic “early life” began 540 million years ago.
This is era is marked by an explosion of life especially in the Cambrian period
Due to differences in life forms and environment the Paleozoic is divided into Early Paleozoic and late Paleozoic

6. Early Paleozoic Geology Life
Supercontinent of Gondwana (South America, Africa, Australia, Antarctica, and parts of Asia)
Life
Dominated by invertebrate sea life

7. Late Paleozoic Geology
At the start of the time Laurasia was formed through the collision of North America and Africa
Towards the end of the eon Laurasia and Gondwana collided to form Pangaea

8. Late Paleozoic Life Plants began moving inland
Plants changed from leafless reeds to forests
Amphibians evolved
Fish began losing their armor

9. Mesozoic “middle life” began ~183 million years ago.
Geology
break up of Pangaea
Life-
Gymnosperm plants develop that do not need to be near water
age of the reptiles (dinosaurs)
progress to shelled egg

10. Cenozoic
The Cenozoic or “era of recent life” began 65 million years ago
Geology
volcanism, mountain building, and earthquakes along the west coast of the US-created the Rocky Mountains
Life
This is the time of mammals and flowering plants

11. Mass extinctions

12. Mass Extinctions
There have been five mass extinctions
The Ordovician-Silurian extinction occurred about 439 million years ago due to a drop in sea levels as glaciers formed followed by rising sea levels as glaciers melted. 25 percent of marine families and 60 percent of marine genera were lost.
The Late Devonian extinction took place somewhere around 364 million years ago. However, evidence supporting an episode of global cooling, similar to the event. Evidence suggests that the extinction was triggered by another glaciation event on Gondwana, which is evidenced by glacial deposits of this age in northern Brazil. This mass extinction killed 22 percent of marine families and 57 percent of marine genera.

13. Mass Extinctions
The Permian-Triassic extinction happened about 251 million years ago and was Earths worst mass extinction. 95 percent of all species, 53 percent of marine families, 84 percent of marine genera, and an estimated 70 percent of land species such as plants, insects and vertebrate animals were killed during this catastrophe. Direct evidence for this period has not been found but many scientists believe a comet or asteroid impact led to this extinction, volcanic eruptions, or impact of the comet or asteroid triggered the volcanism.
The End Triassic extinction, taking place roughly 199 million to 214 million years ago, was most likely caused by the breakup of Pangaea and the opening of the Atlantic Ocean. The volcanism may have led to deadly global warming. Rocks from the eruptions now are found in the eastern United States, eastern Brazil, North Africa and Spain. 22 percent of marine families, 52 percent of marine genera, and an unknown percentage of vertebrate deaths were the result.
Cretaceous-Tertiary extinction occurred about 65 million years ago and is thought to have been aggravated, if not caused, by impacts of several-mile-wide asteroid that created the Chicxulub crater now hidden on the Yucatan Peninsula and beneath the Gulf of Mexico. Yet, some scientists believe that this mass extinction was caused by gradual climate change or flood-like volcanic eruptions of basalt lava from the Deccan Traps in west-central India. During this extinction, 16 percent of marine families, 47 percent of marine genera, and 18 percent of land vertebrate families including the dinosaurs.