Geologic Time

What is Geologic Time?

A relative scale which divides geologic time into units.

Relative time is compared to something.Units are from largest to smallest Eon Era Period Epoch Age

Basis for subdivision

Law of superpositionAge of Earth 4.6 billion yrsAge of oldest rock 4 billion yrsExtinctions

Precambrian Era

Vast time in earth history before the deposition of Cambrian Fossil bearing rocks.

Fossils are rare because animals were soft bodied.

Example: Jellyfish, paramecium, and trail marks from animals.

Plants and animals

Paleozoic Era

Life increased in complexityThe continents collided to form Pangea

Also has “Age of fishes” in itDivided into 6- 7 periods

Cambrian Period- 600 mya

1st common and widespread fossils example: Algae, sponges, worms, mollusksAll lived in the Sea Trilobites- large but few bivalves- clams sea cucumbers

Cambrian environment

Ordovician Period 500-425 mya

Rise of new animals groups of importance.

Oldest vertebrates- fragments of bone example: bryozoans, brachiopods, echnoidsSea covered land uplift and mountain building

Ordovician environment

Silurian Period 425-405 mya

New families rather than new groups of animals

Most important plants (fossil of oldest plant)

Trilobites, crinoids, etc. from ancient reefs near Chicago

types of fish starting

Live fossil

trilobites

live fossil

crinoids

Silurian Environment

Devonian Period 405-345 mya

Expansion of fish and land plants1st land animals (primitive amphibians)First developed fish Jawless fish plate-skinned fish sharks 1st boney fishFrom lobed-fin fish -amphibians

Devonian continued

Oldest spiders, millipedes and insects

Fresh water clamsGreat forests startingCoral reefs

Devonian environment

Carboniferous 345-280mya

Mississippian period 345-310 myaShallow warm seasSea animals and

plants flourishAmphibians and land

plants spreadCoal swamp forests

(most US under water)

Pennsylvanian Period 310-280 myaScale trees, seed

ferns developGiant dragonflies (30 inch wing span)Reptiles from

amphibians

Carboniferous environment

Permian Period 280-230 mya

Primitive conifersNew insects (beetles, and true dragonflies)Active reptiles different from skull and vertebrae fossil eggs example: sail-back lizard (sail as temperature control)Theriodonts – carnivore ( mammals are descendents) A lot become extinct (trilobites, corals, blastoids)

Permian environment

Mesozoic Era

Known as middle LifeAlso has the “Age of the Reptiles” in it.

New pattern of lands and seas, formed mountains ranges

Triassic Period 230-180 mya

A lot of volcanic activityReptiles dominate advanced body structure shell-protected eggs both land and water reptiles1st appeared lobster like creatureConifer forest- Petrified forest

Triassic Environment

Jurassic Period 180-145 mya

Flying reptiles and herbivores in waterOldest mammals-fragments of rat sized jaws

and teeth.

Oldest known bird

Over thousand species of insects

Dinosaurs

3 main groups1. Sauropods: long-necked, long-tailed, four-legged (largest land animal 87 ft long)

2. Stegosaurs: armored reptiles, weighed up to 10 tons

3. Carnivorous Theropods: walk on hind legs

Dinosaurs hips

Dinosaurs are also classified by the two types of hips.

Saurischian- lizard hipped

ornithischian- bird hipped

Cretaceous Period 135-63 mya

Major advanced of seaNew arrivals- flowering plants, trees-

magnolia, oaks, maple, etc.New sources of food provided for mammals,

birds, reptiles, and insectsDinosaurs roamed over all continentsSmall mammals, marsupialsAt the end of period extinction of dinosaurs.

Cretaceous Environment

Cenozoic Era 63-1 mya ( last 70 my)

Two Periods and seven epochs Includes the age of the Mammals

Includes the age of ManBirds are numerousBoney fish dominateOur era of today

Tertiary Period

Has five epochs.A lot of changes taking place examples:-Small mammals to large mammals-Tropical plants to grasses-Single animals to herds-Alps, Himalayas, Rockies, Andes and Glacier formation

Paleocene epoch

Mammals are smallTropical plants

Eocene Epoch

Mammals becoming largerAncestors of modern whale and horse

Oligocene Epoch

Tropical plants replaced by grasses and pinesApes, elephants, cats and dogs families

Miocene Epoch

Herds of grass eating animalsLand bridge between Siberia and Alaska-

Mastodans cross.

Pliocene Epoch

Glaciers began to formSea level fellAnimals crossed land bridges and new land

formedAnimals hunting herds

(Near End of Epoch)Ice age beginsGrand canyon was carved out of rising rock

layers

Grand canyon layers

Quarternary Period

Includes two EpochsClimate much colderIncludes the Ice AgeIncludes the age of manOur period of today

Pleistocene Epoch

2.5 mya Ice AgeGlaciers advanced at least four different

timesAnimals either developed protective covering

or moved south example: mastodons, saber-tooth tigers, mammoths

(At end of the epoch)10,000 yrs ago Ice sheets meltingLarge mammals became extinct

Pleistocene environment

Holocene Epoch

Earth’s climate became warmerHuman civilization arose (Age of man)The epoch of today