Figure 22 Geologic History

Precambrian Time Paleozoic Era 4.6 billion-544 million 544-245 million years ago years ago

Cambrian Ordovician Silurian 544-505 million 505-438 million 438-408 million years ago years ago years ago

Geologic Events • Earth forms about • Shallow seas cover Warm, shallow seas • Coral reefs develop. 4.6 billion years ago. much of the land. cover much of Earth. • Early continents • Oceans form and • Ancient continents Ice cap covers what is collide with what is cover Earth about lie near or south of now North Africa. now North America, 4 billion years ago. the equator. forming mountains. • First sedimentary rocks form about 4 billion years ago.

Development of Life Eurypterid • Bacteria appear about • Great "explosion" • Invertebrates • Fish with jaws 3.5 billion years ago. of invertebrate life dominate the develop. • Soft-bodied, multi• occurs in seas. oceans. r\ • Land plants appear. cellular organisms • Invertebrates with • Early vertebrates— • Insects and spiders 1 develop late in the shells appear, jawless fish—become appear. Precambrian. including trilobites common. • First mass extinction and mollusks. probably occurs near the end of the Precambrian.

V Arachnid

Jellyfish-like animal Paleozoic Era 544-245 million years ago

Devonian Carboniferous 360-286 million years ago Permian 408-360 million Mississippian Pennsylvanian 286-245 million years ago 360-320 million years 320-286 million years ago ago years ago Geologic Events • Seas rise and fall over • Appalachian • Deserts become larger what is now North Mountains begin in tropical regions. America. to form. • The supercontinent • North America and Pangaea forms as all Northern Europe continents join lie in warm, together. tropical region.

Development of Life • Age of Fishes begins • Great swamp forests • Reptiles become as sharks and fish with of huge, woody trees dominant on land. scales and bony cover eastern North • Warm-blooded skeletons become America and parts of Dragonfly reptiles appear. common. Europe. • Mass extinction of • Trilobites and corals • First true reptiles many marine inver• flourish in the oceans. appear. tebrates, including • Lungfish develop. • Winged insects trilobites. • First amphibians appear. reach land.

m Cockroach Dimetrodon

Coal forest Devonian Conifer forest Amphibian Figure 22 Geologic History

Mesozoic Era 245-66 million y

Jurassic 245-208 million years ago 208-144 million years ago

Geologic Events • Pangaea holds together for much • Pangaea breaks apart as North of the Triassic. America separates from Africa • Hot, dry conditions dominate the and South America. center of Pangaea.

Development of Life Archaeopteryx • Age of Reptiles begins. • Largest dinosaurs thrive, including • First dinosaurs appear. Stegosaurus, Diplodocus, and Apatosaurus. • First mammals, which evolve Morganucodon • First birds appear. from warm-blooded reptiles, appear. • First flying reptiles, pterosaurs, • First turtles and crocodiles appear. appear. • Conifers, palmlike trees, and ginkgo trees dominate forests.

Diplodocus Megazostrodon Mesozoic Era Cenozoic Era 245-66 million years aig o 666 milliomime n years ago to present

E etaceous Tertiary Quaternary 144-66 million years ago 66-1.8 million years ago 1.8 million years ago to the present

Geologic Events • Continents move toward • The Rocky Mountains and • Thick glaciers advance and their present-day positions, Himalayas form. retreat over much of North as South America splits • Continents continue to move America and Europe, parts from Africa. into present-day positions. of South America and Asia, • Widespread volcanic • Continental glacier covers and all of Antarctica. activity occurs. Antartica.

Development of Life Magnolia • First flowering plants appear. • Flowering plants thrive. • Mammals, flowering plants, • Dinosaurs, including • First grasses appear. and insects dominate land. Tyrannosaurus rex, dominate. • Age of Mammals begins. • Modern humans evolve in • First snakes appear. • Modern groups such as Africa about 100,000 years • Mass extinction at end of horses, elephants, bears, ago. period causes disappearance rodents, and primates appear. • Giant mammals of North of many land and marine life • Ancestors of humans evolve. America and Eurasia forms, including dinosaurs. become extinct when the ce Age ends about 10,000 years ago.

4.4^ Tyrannosaurus

Creodonts Hyracotherium Homo sapiens