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% C14 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 (65mya 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 currentlyThis leads to earth

quakes and rising mountain ranges