The History of Earth and Life Early History

The History of Earth and Life

Early History of Earth � Though we can’t 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

History in Rocks � There is direct evidence of life’s existence 3. 9 billion years ago found in the oldest rocks found on earth � Fossils provide this evidence

Fossils 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

Paleontology � 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

Fossil Formation � 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

How do we know how old something is? � Scientists utilize 2 types of dating to determine age of fossils › 1. Relative Dating › 2. Radiometric Dating (carbon dating)

Relative 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

Radiometric Dating � 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

Half lives �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 vs Potassium 40 � Carbon 14 is used to date things 60, 000 years ago or younger � Potassium dates things that are much older

Practice � 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% C 14 to 50% decayed � After 5730 more years= 25% 14 to 75% decayed � � So 5730 + 5730 = 11, 460 years old

Earth’s time scale

Life during the Precambrian (4000 -543 million years ago) � 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

Diversity during the Paleozoic (543 -248 mya) � 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

Diversity during the Mesozoic � 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

Diversity during the Cenozoic (65 mya to current) � Mammals begin to flourish and take on all sizes � Primates appear � Human fossil are found starting about 200, 000 years ago

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