Ch 9-View of Earth’s Past

• Objectives– Summarize how scientist worked together to develop geologic

column– List major divisions of geologic time– Summarize how evolution is related to geologic change– Identify characteristics of Precambrian rock– Identify major geologic and major biological developments

during Paleozoic Era– List periods of Mesozoic and Cenozoic Era– Identify major geologic and biological developments during

Mesozoic Era– Identify major geologic and biological developments during

Cenozoic Era

Geologic Column

• Geologic time scale-scale outlines development of Earth and life on Earth– Used to describe sequence and length of this change

• Geologic column-ordered arrangement of rock layers based on relative ages of rocks in which oldest rocks are at bottom– Use column to estimate age of rock layers, cannot be dated

radiometrically– Compare rocks w/ similar layers that have same fossils or same

relative position

• Principle of faunal succession-group of fossil plants and animals occur in the geologic recorded in a definite and determinable order. A period of geologic time can be recognized by its respective fossils

Major Divisions of Geologic Time

• Earth’s history marked by major changes in Earth’s surface, climate, types of organisms

• Cenozoic Era (65.5 million yrs-present)– Complex human societies develop– Large carnivores appear– 1st primates appear– Woolly mammoths appear

• Mesozoic Era (251-146 million yrs)– Flowering plants and modern birds appear– Mass extinction ends Mesozoic Era– Jurassic Period-Dinosaurs dominant life form

• Paleozoic (542-299 million yrs)– Pangaea comes together, mass extinction

ends Era– Shelled marine invertebrates appear– Atmosphere reaches modern O2 rich state– Seed bearing plants develop

• Pre-Cambrain Time (4.6 billion yrs)– Earth forms– Continental shields appear– Fossils are rare– Stromatolites are most common organism

Eons and Eras

• Eon-largest unit of geologic time

• 4 eons– Hadean, Archean, Proterozoic, Phanerozoic– 1st 3 in Pre-cambrain– Phanerozoic divided into eras-Paleozoic,

Mesozoic, Cenozoic

Periods and Epochs

• Periods-eras divided into shorter time units– Usually named for the place where its

characteristic fossils were first discovered

• Epochs-divided into smaller units of time– Defined by occurrences of distinct fossils in

fossil record

Sec 2-Precambrain Time and Paleozoic Era

• Define evolution– Gradual development of new organisms from

pre-existing organisms– Heritable change in the characteristic w/in

population from one generation to next– Natural selection

• Evolution and Geologic Time– Major geologic and climate changes can

affect ability of some organisms to survive– Sea level=coastal areas

Precambrian Time

• Earth 4.6 billion yrs old

• Formation of Earth ended 342 million yrs ago

• 88% of Earth’s history

• Record difficult to interpret

• Rocks severely deformed and altered by tectonic activity

Precambrian Rocks

• Shields-large areas of exposed Precambrian rocks– Exist on every continent– Result of volcanic activity, mt building,

sedimentation, metamorphism– Half of valuable mineral deposits in

Precambrian rock-nickel, iron, gold, copper

Precambrian Life

• Lacked bones, fossils rare

• Folding, faulting, erosion destroyed most of fossils

• Stromatolites-reef like deposits formed by blue green algae

• Marine worms, jelly fish, single celled org

Paleozoic Era

• 545-251 million yrs ago-at beginning land masses were scattered than came together to form Pangaea

• Cambrian Period-life thrives in shallow, warm waters– Trilobites-most common Cambrian inverts. Used

as index fossils– Brachiopods-group of shelled animals. 2nd most

common animal in Cambrian• Worms, jellyfish, snails, sponges

• Ordovician Period-Trilobite populations dwindle– Clamlike brachiopods and cephalopod mollusks

become dominant– Large number of corals appear– Graptolites-tiny invert that flourished in oceans,

primitive fish appear. No plant life on land

• Silurian Period-Verts and inverts marine life continue to thrive– Echinoderms more common– Eurypterids-scorpion like sea creatures– Plants evolve on land

• Devonian Period-age of fishes– Land plants-horsetails, ferns, seed bearing plants

• Carboniferous Period-Climate warm, humidity extremely high– Forests and swamps cover land– Coal deposits in Penns, Ohio, W. Virginia-

remains of forests

• Permian Period-mass extinction of large number of Paleozoic life forms– Continents joined to form supercontinent of

Pangaea-Appalachian Mts– Fossils indicate reptiles and amphibians

survived environmental changes-dominated Earth

Sec 3-Mesozoic and Cenozic Era

• What happened at the end of Permian Period?– 90% of marine organisms and more than 70%

land organisms died

• What is a mass extinction?– An episode during which large numbers of

species become extinct

Mesozoic Era

• Periods of Mesozoic Era-Triassic, Jurassic, Cretaceous

• 251-65.5 million yrs ago

• Age of Reptiles

• Pangaea broke up

• Sierra Nevada and Andes Mts formed. How?

• Triassic Period-dinosaurs appear, lush forests w/ cone bearing trees and cycads– Ammonites serve as index fossil– 1st mammals appear-small rodent like

• Jurassic Period-dinosaurs dominant– Saurischians and Ornithischians– 50 tons and 25 m long– Flying reptiles common– Modern bats

• Cretaceous Period-dinosaurs continue to dominate– Tyrannosaurs rex-6 m tall, huge jaws w/ sharp

teeth– Plant life becomes sophisticated– Angiosperms appear

Cretaceous-Tertiary Mass Extinction

• Ended in mass extinction

• No dino fossils found after this period

• Caused by environmental changes-result of movement of continents and increased volcanic activity

• Impact hypothesis-giant meteorite crashed into Earth 65 million yrs ago

Cenozoic Era

• 65.5 million yrs ago

• Age of Mammals

• Continents moved to present day position

• Alps and Himalayas formed by tectonic plates

• Dramatic changes in climate-continental ice sheets covered 1/3 of Earth’s land– What did this lead to?

• Temps decreased

Periods

• Tertiary-time before last ice age• Quaternary-time w/ last ice age and includes

present• Divided in 7 epochs

– Paleocene and Eocene-1st primates evolved, earliest ancestor of horse, fossils indicate first whales, small reptiles still flourish. Temps decreased

– Oligocene and Miocene-Himalayas formed, climate became cooler and drier, early mammals became extinct. Deer, pigs, horses, camels, cats, dogs flourished. Antarctic icecap formed, Mediterranean Sea filled and dried up several times

• Pliocene Epoch-Bear, dog and cat families evolved into modern forms, herbivores flourished. Sea level fell due to increase in ice, C America land bridge formed

• Pleistocene Epoch-began 1.8 million yrs ago, ice sheets advanced and retreated several times. Earliest modern humans were discovered-hunters

• Holocene Epoch-began 11,500 yrs ago, as the last glacial period ended, sea levels rose due to increase in sea level, coastlines took modern shape, N American Great Lakes formed, modern humans developed agriculture, and tools