Earth was formed 4.6 billion years ago but it was not friendly to life hot gases and volcanic eruptions filled the atmosphere around 3.9 billion years ago the earth began to cool rain began to fill depressions in the earth creating oceans.

300 million years ago Earth did not have seven continents but one massive super continent called Pangaea surrounded by one ocean called panthalassa the explanation for Pangaea was earths surface was broken up due to plate tectonics, due to the churning and circulation in the earths mantle this super continent broke up.

Geologist and paleontologist examines rocks and fossils to determine the age and what the earth was like long ago, fossils show us evidence of early organisms and they're behavior Most fossils form in sedimentary rock like sand and clay and compressed over long periods of time There is two different types of fossils trace and body Trace:imprints food feces Body:animal or plant bones

When determining age there is two different types of methods relative dating and radioactive dating relative dating is when rock is built up over time and the deeper a fossil is the older it is but relative dating cannot always tell us the exact age while radioactive uses the half life of an isotope to determine age .

Our Earths history is broken down into four eras The Precambrian era , Paleozoic,Mesozoic and Cenozoic era these eras were determined by what organisms lived there at that time.

The Precambrian era was about 3.5 billion years to 543 million years ago this era makes up about 87% of our earths history organisms developed the ability to photosynthesize 2.7 billion years ago in this era these organisms were single celled prokaryotic ,sponges and jelly fishes. The time periods in this era was Hadean, Archean,and Proterozoic.

The Paleozoic era lasted until 245 million years ago life begins to diversify according to fossil records there were many different animals and plants invertebrates and vertebrates are developed in this era organisms in this era includes worms,sea stars,arthropods and amphibians the Cambrian explosion also took place in this era at the end of this era there was the largest mass extinction 90% of marine life was extinct and 70% of land species went extinct. The time periods in this era were Cambrian, Ordovician,Silurian,Devonian,carboniferous, and Permian.

The Mesozoic era lasted until 66 million years ago more complex organisms such as dinosaurs,mammals,and birds developed in this era in this era there was a large mass extinction of the dinosaurs as well as the separation of the continents .The time periods in this era was Triassic , cretaceous, and Jurassic.