History of the Earth

By: Kara Lehner

1. The Formation of Earth

During the Precambrian Period, a swirling cloud of gas and dust was created from exploding stars or supernova. This orbiting mass accumulated and larger pieces of mass started colliding with it. Because of the breakdown of radioactive elements, and the constant contraction that put pressure on the Earth, it was a molten mass.

2. Earth's Crust Forms

The oldest rock was created when molten lava rose from cracks in the seafloor about 3.8 billion years ago in the Precambrian Period. The rock cooled and hardened creating Earth's early crust. These early rocks are thought to have had the first traces of bacterial life.

6. Plants Begin to Grow on Land

430 million years ago, during the Silurian Period, plants began to grow on land although it was very difficult. Because it was difficult, plants grew tube-like tissues to transport water and nutrients from the water to land. The first plants grew on mushy ground and were not very tall.

7. Largest Mass Extinction Ever!

During the largest mass extinction in Earth's history, 95% of marine animals and 70% of land animals died off. This wipe-out during the Permian Period was thought to have been caused by climate change because of evidence that shows rapid global warming and cooling. Because of the speed of which it happened many animals did not have the time to adjust causing them to die.

8. The Age of the Dinosaurs

240 million years ago a kangaroo-sized animal that was a plant eater and was known as the prosauropods was born. More commonly known dinosaurs such as the Tyrannosauruses Rex were not alive during the Triassic Period but during the Jurassic Period. During the Jurassic Period, dinosaurs dominated the Earth for about 150 million years. There was a wide variety of different dinosaurs, some were plant eaters and some meat eaters.

9. The Beginning of Ice Ages

Ice ages began to take over Earth starting 1.8 million years ago. The size and intensity of each varies, however, each was linked to variations of the Earth's orbit around the sun. These ice ages led to the rise of animals such as woolly mammoths, mastodons, and woolly rhinos, all of which are now extinct. Ice ages ceased to exist because the Earth fell into a normal orbit around the sun.

10. The First Modern Humans

About 190,000 years ago, during the Quaternary Period, humans or homo sapiens were born. Around 70,000 years ago humans began to venture out from Africa to places such as Australia and South America. Groups also spread out to Europe and Asia where they were hunters or gatherers. Life has continued to evolve causing it to be the way it is today.