Though we cant be certain, scientists have suggested that the earth was very hot due to volcanoes and meteorites hitting the earth Sometime around 4.4 billion years ago, the earth appears to have started cooling, leading to water condensation and ocean formation

There is direct evidence of lifes existence 3.9 billion years ago found in the oldest rocks found on earth Fossils provide this evidence

A fossil evidence of an organism that lived long ago found embedded in rock Fossils provide clues to what life looked like long ago There are 5 different types of fossils 1. Trace Fossils 2. Casts 3. Molds 4. Petrified/permineralized fossils 5. Amber preserved or frozen

Is the study of fossils in order to understand events and organism of long ago Fossils indicate what animals looked like, how big they were, how they moved, climate and more

For fossil formation, organisms typically need to be buried in sand or mud and have more deposits on top of them Compression from above layers causes the organism to harden and turn into rock Sedimentary rock offers low temperatures and pressures which help with fossil formation

Scientists utilize 2 types of dating to determine age of fossils 1. Relative Dating 2. Radiometric Dating (carbon dating)

Utilizes fossils position in rock layers to determine relative age So if soil is undisturbed, then 1. Deeper fossils are older 2. fossils in the same level are of the same age

Scientist use rocks near the fossils and analyze their chemical composition to determine age base on radioactive isotope ratios Radioactive chemicals decay at a constant rate and based on istopte composition age determined easily Half lives are used to calculate age

A half life is the time it takes half (50%) of the radioactive isotope to a new isotope after it decays For Example Potassium 40 decays to Argon 40 with a half life of 1.3 billion years Radioactive Carbon 14 decays with a half of life of 5730 years

Carbon 14 is used to date things 60,000 years ago or younger Potassium dates things that are much older

If a rock is found that has 25% composition of the original carbon 14 (with 75% already decayed), how old is it? (half life is 5730 years) After 5730 years= 50% C14 to 50% decayed After 5730 more years= 25% 14 to 75% decayed So = 11,460 years old

Era where the oldest fossils are found Photosynthetic bacteria (stromatolites) are found in rocks this old All life is unicellular, but as time progresses the fossil record shows a shift from prokaryotes to eukaryotes Near the end, sponges and jelly fish are found

First vertebrates (fish) appear First amphibians First seed plants First reptiles First conifers appear Ended with the largest mass extinction know to earth (about 90% all species went extinct

First dinosaurs First mammals (small) First flowering plants First birds Ended with another mass extinction that killed most dinosaurs (75% of life extinct) First evidence of continent seperation

Mammals begin to flourish and take on all sizes Primates appear Human fossil are found starting about 200,000 years ago

The continents together before they divided Every continent is slowly shifting currently This leads to earth quakes and rising mountain ranges