Fossils

What is a fossil? preserved remains of a living thing Paleontologist preserved remains of a living thing scientist who studies fossils

How do fossils form? Fossil Formation living things die buried by sediment sediment hardens preserved in rock Fossil Formation

Types of Fossils a mark or cavity made in a sedimentary surface by a shell or other body. copied shape of organism fills in empty space of mold Mold Cast

Types of Fossils Petrified Fossil Trace Fossil minerals replace organism “turned to stone” evidence of ancient organisms ex. footprints

Organisms preserved in: Tar Amber (hardened sap) Ice Preserved Remains

Fossil Record shows how organisms have changed over time supports the theory of evolution Fossil Record

Fossils provide a past environments picture for: past climates changes in Earth’s surface

Finding Relative Age

Relative Age Absolute Age -age compared to age of other rocks -number of years since the rock formed -calculated by radioactive decay

Law of Superposition -used to determine relative age of rock - layering of sediment -the oldest layer is at the bottom youngest layer at the top in undisturbed sequences.

Geologic Column Disturbing Forces An ideal sequence of rock layers. Makes it easier to identify difficult ones. Some layers are disturbed by forces within the Earth, which causes some layers to not be horizontal.

Disturbed Forces Unconformity Disturbing events are always younger than rock layer they disturb. Faults, intrusions, folding, tilting. -gap in geologic record. Missing part of geo column. Non-deposition or erosion.

Using Fossils to Date Rocks -geologists give a relative age to a layer -also give same age to matching layers at other locations -help geologists match rock layers 1. widely distributed 2.organism that existed briefly -tell relative age of layers in which they occur Using Fossils to Date Rocks Index Fossil

Radioactive Dating

Absolute Dating Radioactive Decay To determine absolute age: the # of years existed. Analyze unstable isotopes of radioactive elements. Isotope: atoms of the same element that have the same number of protons but difference numbers of neutrons. -elements break down and release particles and energy at a steady rate.

-time it takes for half of a radioactive atom to decay Rate of Decay Half-life -rate is constant (never changes) -called half-life -time it takes for half of a radioactive atom to decay

Types of Radiometric Dating determine absolute age 1. determine amount of radioactive element in rock 2. compare with amount of stable element in rock

Potassium- Argon Dating Uranium-Lead Dating -potassium 40 decays to stable argon Potassium-40 has a half-life of 1.3 billion years. Uranium 238 decays to lead- 206 Half-life of uranium-238 is 4.5 billion years

Rubidium- Strontium Dating Carbon-14 Dating Rubidium-87 decays to Strontium-87. Half-life of rubidium- 87 is 49 billion years. Carbon-12 and Carbon-13 are stable isotopes and Carbon- 14 is radioactive. When animal decays, carbon-14 has half-life of 5,730 years. Dates more recent things (mammoths, fossils, etc.)

How old is Earth? -Scientists think Earth is even older -oldest rocks found - 4 billion years old -Scientists think Earth is even older

The Geologic Time Scale

Geologic Time Scale -record of life forms and events in Earth’s history -changes in life forms mark where one unit of time ends & the next begins

Divisions of Time Eras -scale begins with Precambrian Time -divided into eras periods epochs -long units of time -three eras: Paleozoic Mesozoic Cenozoic

Periods Epochs -divisions of eras -10,000,000 to 2,000,000 years -ex. Jurassic Cretaceous -divisions of Cenozoic period -more events took place; more fossils to sort

Earth’s History

Precambrian Time -Earth formed from dust and gas 4.6 billion years ago -pulled together by gravity -interior became hot & molten -after millions of years, lava flowed over surface -lava built the 1st continents -earliest life similar to today’s bacteria (formed 3.5 billion y.a) -photosynthesis began 2.5 b.y.a -organisms had soft bodies, left few fossils -jellyfish

Paleozoic Era Vertebrate -many new organisms evolved -many had hard shells/skeletons C -all animals lived in sea C -jawless fish evolved: *1st vertebrates O -animal with a backbone -plants began to grow on land S -first insects also appeared -many fish lived in seas -animals also began to go on land D -lungfish: 1st vertebrates on land -evolved into amphibians C

Amphibians Reptile Mass Extinction -lives part of life on land, part in water -reptiles started to evolve -scaly skin, lays eggs -end of Paleozoic era, many organisms died out -many types of living things became extinct at same time -cause unknown -one theory: climate change -killed 95% of ocean life -fish and reptiles survived

Pangaea -supercontinent formed 260 million years ago -caused major climate changes -many organisms died -after formed, broke apart again

Mesozoic Era

Mesozoic Era Triassic Mammal -three periods: Triassic, Jurassic, Cretaceous -“Age of Reptiles” -225 million y.a., 1st dinosaur appeared (Coelophysis) -mammals also appeared -warm-blooded vertebrate that feeds its young milk -evolved from warm-blooded reptiles Mesozoic Era Triassic Mammal

Jurassic -dinosaurs dominant on land -plant eaters and meat eaters -“ruled” Earth for 150 mill. years -one of first birds appeared *Archaeopteryx “ancient winged thing” -paleontologists think birds evolved from dinosaurs

Cretaceous -reptiles still dominant -meat eaters, like T- rex, ruled the land -mammals still evolving -flying reptiles became extinct -flowering plants evolved -at the end, another mass extinction occurred

Theories of what caused the mass extinction -One theory: an asteroid struck the Earth -threw huge amounts of dust and vapor into the air -many organisms died instantly -blocked sunlight for years -many died from starvation -no dinosaurs survived -Another theory: volcanic activity caused major climate change Theories of what caused the mass extinction

Cenozoic Era Tertiary -Age of Mammals -mammals evolved adaptations to live in many different environments -climate warm and mild -whales & dolphins appeared -grasses evolved; providing food

Quaternary -climate cooled causing Ice Age -much of Earth’s waters froze -climate began to warm 20,000 years ago; melted glaciers -ocean life flourished -flowering plants and mammals became common (bats, cats, dogs, cattle, humans) -human ancestors appeared 3.5 million years ago -modern humans evolved 100,000 years ago

Evolution and Natural Selection Chapter 7

Species - A group of organisms - Can mate and reproduce Adaptation - A characteristic - Helps an organism survive and reproduce Evolution - A process - Gradual change over time Extinct organism no longer exists organism did not adapt or evolve

Ways to Compare Organisms 1. Compare skeletons 2. Compare DNA

- Studied evolution on Galapagos Islands Charles Darwin - studied fitches (birds) - Some organisms are more adapted Natural Selection - They have higher chance of surviving - Will produce more offspring