Prehistoric Earth Objective 8-10

The Big Bang Theory At the beginning of time... The universe existed at a single point All the matter and energy exploded This created the universe 12 billion years ago As the matter spread out it collected into massive pieces (due to gravity) This created the first stars and planets

Earth Earth was created 4.6 billion years ago It was a bunch of debris pulled together by gravity

Earth It was bombarded for about 100 million years by meteors (some as large as the planet mars) This caused Earth to melt and reform with a molten core and solid surface 4 billion years ago

Earth The atmosphere was made of gasses poisonous to us 3.8 billion years ago the Earth’s surface cooled enough for water to exist in liquid form It rained for millions of years The oceans were born Earth was ready for life to begin

Life! Simple molecules formed organic molecules Scientists Miller and Urey ran an experiment that proved this From organic molecules life was born Prokaryotic organisms existed in abundance by 3.5 billion years ago

Review How old is the earth? When did the oceans form? When did the first living things evolve?

Eukaryotes Prokaryotes dominated for 2 billion years They filled the sky with oxygen and nitrogen Eukaryotes evolved 1.2 billion years ago Endosymbiotic Theory: two or more prokaryotes came together to form a single eukaryote

Precambrian Time All of this time, from the beginning of the earth until the Cambrian Explosion is called Precambrian Time Precambrian Time lasts from 4.6 billion years to 544 million years (.544 billion)

Eras & Periods After Precambrian Time the remaining 544 million years (my) is broken into three eras Eras are very large blocks of time marking major macroevolutionary events Eras are further broken into periods which are smaller chunks of time marking smaller significant evolutionary events

Eras & Periods Paleozoic (multicellular) 225my – 544my Cambrian (Cambrian Explosion) Ordovician Silurian Devonian Carboniferous Permian (Permian Extinction 95% of all life)

Eras & Periods Mesozoic (Age of Reptiles) 65my – 225my Triassic Jurassic Cretaceous (mass extinction 50% of all life) Cenozoic (Age of Mammals) Now – 65my Tertiary Quaternary

Review How did oxygen get into the air? How long was Precambrian Time? What are the 3 eras after Precambrian Time?

How Science Knows Scientists can date rocks and fossils using dating techniques Relative dating Radioactive dating Once we know the age of the rocks we can observe their current condition, compare that to their age, and put the pieces together like a puzzle A lot is just guess work

Fossils Fossils are petrified (turned to stone) remains or clues of animals that once lived Fossils can be: eggs skeletons (or pieces of skeletons) foot prints poop

Fossils

Relative Dating The rocks of this planet are in layers The type of rock in each layer tells us a little bit about the earth We can get approximate dates of each layer and of the fossils located in those layers Index Fossils are used as references for other fossils

Index Fossils Index Fossils are species that lived over a wide area for a short time The wide area makes them useful for determining a larger range of species The short time makes them useful for determining when they and other fossils existed

Radioactive Dating Rocks are made of atoms Some atoms are unstable (radioactive) and break down over time We can measure this decay using half- lives Half-life is how long it takes half the radioactive atoms in a sample to decay Radioactive dating is a much more specific measurement than relative dating

Radioactive Dating

What we learn from Fossils Dating determines the age of fossils From the fossils collected biologists have created a tree of life 99% of all species lived and died (went extinct) before we arrived on the planet Life survived massive extinction through its vast diversity

Review What are the two types of dating? How are they different? Why are index fossils important? What types of fossils have been found?