Prehistoric Earth Prehistoric Earth Geologic Time Scale Earths

Geologic Time Scale Earth’s history is divided into time units based on: • Major

Eras- 2 nd longest time subdivision based on major worldwide changes in types of

Phanerozoic Eon Cenozoic Era Mesozoic Era Quaternary Period Tertiary Period Cretaceous Period Age of

Organic Evolution The fossil record shows that species have changed over geologic time. Environmental

Species ØGroup of organisms that normally reproduces with other members of their group. ØReproduction

Natural Selection ØA process by which organisms with characteristics that are suited to a

Earth’s History Precambrian Time Ø Ø Earth is about 4. 5 billion years old.

ØVery few rocks are found that date back to 4 billion yrs ago. ØEarth

Primitive Atmosphere • Atmosphere started out as a lightweight mixture of Hydrogen & Helium,

Precambrian Life • The first organisms to form on Earth (3. 5 bya) were

• Over millions of years, the levels of Oxygen increased in the oceans

Paleozoic Era (544 mya to 248 mya) Paleozoic Life Trilobite Placoderm • Invertebrate animals

• Amphibians take control at the end of the Paleozoic. Eryops • Ferns

Paleozoic Geology • Pangaea forms near the end of the Paleozoic. • The largest

Mesozoic Era (248 mya to 65 mya) Mesozoic Life • Reptiles (Dinosaurs) most abundant

• The 1 st mammals appear during the Triassic Period • The 1

Mesozoic Geology • Pangaea breaks apart into Gondwanaland & Laurasia during the early Mesozoic.

• Many factors could have led to the extinction: § Plate Tectonics causing

Cenozoic Era (65 mya to present day) Cenozoic Life • Mammals become the most

• The largest of the mammals becomes extinct during the Cenozoic. • Homo

Fossils Principle of Superposition Ø In undisturbed rock layers, the oldest layers of rock

Forming Fossils Ø An organism must be buried quickly to form a fossil. Ø

Fossil Type Description Mold hollow impression of a living thing in rock after it

Dating Fossils Radioactive Decay • Some isotopes are unstable and decay into other isotopes

Radiometric Ages • The ratio of the parent isotope to daughter product can be

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Prehistoric Earth

Geologic Time Scale Earth’s history is divided into time units based on: • Major geological events • Major life forms • Mass extinctions Eons- longest time subdivision based on the abundance of certain types of fossils

Eras- 2 nd longest time subdivision based on major worldwide changes in types of fossils. (Paleozoic, Mesozoic, & Cenozoic) Periods- 3 rd longest time subdivision based on types of life that existed worldwide. Epochs- smallest time subdivision characterized by differences in regional life.

Phanerozoic Eon Cenozoic Era Mesozoic Era Quaternary Period Tertiary Period Cretaceous Period Age of Mammals Jurassic Period Age of Reptiles Triassic Period (Dinosaurs) Paleozoic Era Mass Extinction 1 st Flowering Plants First Birds Pangaea Breaks Apart Largest Mass Extinction Permian Period Pennsylvanian Period First Humans Age of Amphibians Mississippian Period First Reptiles First Amphibians Silurian Period Age of Fishes Ordovician Period Age of Cambrian Period Invertebrate s First Land Plants First Fish First Trilobites Devonian Period First single celled organisms

Organic Evolution The fossil record shows that species have changed over geologic time. Environmental changes can affect an organism’s survival. Organisms that can not adapt physically or genetically will not survive.

Species ØGroup of organisms that normally reproduces with other members of their group. ØReproduction is the key to the survival of a species.

Natural Selection ØA process by which organisms with characteristics that are suited to a certain environment have a better chance of surviving & reproducing. ØGenetic mutations can help or destroy a species’ survival.

Earth’s History Precambrian Time Ø Ø Earth is about 4. 5 billion years old. Longest portion of Earth’s history (88%) including the Hadean, Archaen, & Proterozoic Eons.

ØVery few rocks are found that date back to 4 billion yrs ago. ØEarth was a ball of magma for at least a billion yrs.

Primitive Atmosphere • Atmosphere started out as a lightweight mixture of Hydrogen & Helium, which drifted out into space. • It was replaced by large amounts of Nitrogen, Carbon dioxide, Sulfuric acid, & small amounts of Water Vapor (from volcanoes. ) • Eventually the Earth cooled and the rain formed the primordial oceans.

Precambrian Life • The first organisms to form on Earth (3. 5 bya) were bacteria that lived in the toxic oceans feeding on sulfur chemicals. • Cyanobacteria used chlorophyll for photosynthesis to make food & produce Oxygen. • Fossils of cyanobacteria are called stromatolites.

• Over millions of years, the levels of Oxygen increased in the oceans & atmosphere. • Current Atmosphere = 79% Nitrogen 20% Oxygen 1. 0% Argon Water Vapor CO 2 & other

Paleozoic Era (544 mya to 248 mya) Paleozoic Life Trilobite Placoderm • Invertebrate animals populate the oceans at the beginning of the Paleozoic Era. Trilobites are the most abundant. • Prehistoric bony fishes become the most abundant organism during the middle of the Paleozoic.

• Amphibians take control at the end of the Paleozoic. Eryops • Ferns & cone-bearing plants (Gymnosperms) grow on land. • Early forms of reptiles first appear on land near the end of the Paleozoic. Crinoid (Sea Lily) animal not plant!

Paleozoic Geology • Pangaea forms near the end of the Paleozoic. • The largest mass extinction in Earth’s history kills 90% of all marine life & 70% of land species (Permian Period. )

Mesozoic Era (248 mya to 65 mya) Mesozoic Life • Reptiles (Dinosaurs) most abundant organism on Earth. • Reptiles are the 1 st vertebrate to live entirely out of the water.

• The 1 st mammals appear during the Triassic Period • The 1 st birds evolve from dinosaurs during the Jurassic Period. • The 1 st flowering plants (Angiosperms) evolve during the Cretaceous period.

Mesozoic Geology • Pangaea breaks apart into Gondwanaland & Laurasia during the early Mesozoic. • The 2 nd largest mass extinction in Earth’s history kills many marine & land species including the dinosaurs. Chicxulub was Mt. Everest size!

• Many factors could have led to the extinction: § Plate Tectonics causing climate changes § Comet/Asteroid hit the Earth § Blocking out of the Sun § Cooling temperatures § Starvation

Cenozoic Era (65 mya to present day) Cenozoic Life • Mammals become the most dominant organism on Earth. • 3 groups of mammals evolve: § Monotremes § Marsupials § Placentals

• The largest of the mammals becomes extinct during the Cenozoic. • Homo sapiens appear about 140, 000 years ago (according to the fossil record) and becomes the most dominant/complex animal.

Fossils Principle of Superposition Ø In undisturbed rock layers, the oldest layers of rock are on the bottom. Ø Rock layers can be ranked by relative age. Red Sandstone Dinosaur bone Tan Limestone Gray Limestone Tan Sandstone Brown Sandstone Black Shale Brown Sandstone small fossil Green Shale Gray Shale Dike Trilobite fossil

Forming Fossils Ø An organism must be buried quickly to form a fossil. Ø Hard parts dissolve to leave a mold. Ø A cast is formed when a mold fills w/ sediment or minerals. Ø Thin carbon films remain in the shapes of dead organisms.

Fossil Type Description Mold hollow impression of a living thing in rock after it rots away Cast solid mineral deposit that filled a mold, leaving a copy of the living thing Imprint an impression in rock made by a living thing during its life activities Petrification plant or animal tissue replaced by minerals Whole Organism (not a fossil) an entire plant or animal encased and preserved in ice, sap, or another material Trace (not a fossil) remains of tracks, burrows, eggs + eggshells, nests, droppings, etc Picture Fossilized poop

Dating Fossils Radioactive Decay • Some isotopes are unstable and decay into other isotopes & particles. • Decay is measured in halflives, the time it takes for half of a given isotope to decay. Parent 1 Half Life 2 Half 3 Half Lives 4 Half Lives

Radiometric Ages • The ratio of the parent isotope to daughter product can be used to determine the absolute age of the rock. • Living organisms less than 75000 years old can be dated using Carbon-14.