Earth ScienceEarth Science

November 12, 2005November 12, 2005

Dr. ClodfelterDr. Clodfelter

The Geologic Time ScaleThe Geologic Time Scale

The history of the Earth is broken up into a hierarchical set of divisions for describing geologic time

The Geologic Time Scale, cont.The Geologic Time Scale, cont.

Highlights of recent fossil finds from throughout geologic time (from most ancient to most recent) are:

• Precambrian Era: the first fossil bacteria, sponges, corals, and algae appear

• Cambrian Period: abundant invertebrate fossils such as mollusks, crustaceans

The Geologic Time Scale, cont.The Geologic Time Scale, cont.

• Triassic Period: the first fossils of primitive dinosaurs appear

• Jurassic Period: the first fossil mammals and birds; first fossil flowering plants appear

• Cretaceous Period: large fossil dinosaurs appear

Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

Precambrian

Precambrian EonPrecambrian Eon4.5 Billion to 543 Million Years Ago4.5 Billion to 543 Million Years Ago

• Nearly 4 thousand million years after the Earth began

• The first animals left their traces

• Makes up roughly 7/8 of the Earth's history

Archaean EraArchaean Era3.8 to 2.5 Billion Years Ago3.8 to 2.5 Billion Years Ago

• The atmosphere was very different from what we breathe today

• The Earth's crust cooled enough that rocks and continental plates began to form

• Life first appeared on Earth – bacteria microfossils

Phanerozoic EonPhanerozoic Eon543 Million to 543 Million to

• Majority of macroscopic organisms, fungal, plant and animals lived

• Appearance of animals that evolved external skeletons – like shells – and animals that formed internal skeletons – like vertebrates

Paleozoic EraPaleozoic Era543 to 248 Million Years Ago543 to 248 Million Years Ago

• In the beginning, multicelled animals underwent a dramatic "explosion" in diversity

• At the end, the largest mass extinction in history wiped out approximately 90% of all marine animal species

Paleozoic EraPaleozoic Era543 to 248 Million Years Ago543 to 248 Million Years Ago

Mesozoic EraMesozoic Era248 to 65 Million Years Ago248 to 65 Million Years Ago

• Mesozoic means "middle animals”

• Lasted 70 Million Years

• Time of transition

• The world-continent of Pangaea existed

• The time in which life as it now exists on Earth came together

• Important today because of the fossils and oil left behind

Mesozoic EraMesozoic Era248 to 65 Million Years Ago248 to 65 Million Years Ago

Divided into three time periods:

– the Triassic (245-208 Million Years Ago)

– the Jurassic (208-146 Million Years Ago)

– the Cretaceous (146-65 Million Years Ago)

Dinosaurs in the Mesozoic EraDinosaurs in the Mesozoic Era

Dinosaurs...– Evolved in the Triassic Period– Became more diversified in the Jurassic

Period– Became extinct in the late Cretaceous Period– Fossils of some of the last dinosaurs to walk

the Earth can be found in Montana

The Cretaceous/Tertiary The Cretaceous/Tertiary Boundary in MontanaBoundary in Montana

Cenozoic EraCenozoic Era

• The most recent of the three major subdivisions of animal history– The other two are the

Paleozoic and the Mesozoic

• Spans only about 65 million years

• Sometimes called the “Age of Mammals”

A Continental Jigsaw Puzzle: A Continental Jigsaw Puzzle: Putting the Pieces TogetherPutting the Pieces Together

• 1911• German meteorologist • Alfred Wegener• theorized that about 300

million years ago all the continents we know today were joined together in a single continent

• he named it “Pangaea” (pronounced Pan JEE uh)

A Continental Jigsaw Puzzle: A Continental Jigsaw Puzzle: Putting the Pieces Together, cont.Putting the Pieces Together, cont.

• Wegener suggested that Pangaea split apart and its pieces began to “drift,” or move away from each other

• He put together his own evidence, as well as others’, to support his Theory of Continental Drift

A Continental Jigsaw Puzzle: A Continental Jigsaw Puzzle: Putting the Pieces Together, cont.Putting the Pieces Together, cont.

• At first, Wegener’s ideas were very popular because his evidence seemed quite convincing

• Yet a number of observations still remained unexplained– What forces caused the continents to move?

• Due to these remaining problems, Wegener’s theory rapidly lost support and continental drift became “just another theory”

What are Crustal Plates?What are Crustal Plates?

• Earth’s crust isn’t one continuous surface like the skin of an orange

• It is made up of gigantic pieces, like pieces of a jigsaw puzzle

• Each piece is called a crustal plate

• Some plates form the floor of the oceans while other carry the continents

Crustal PlatesCrustal Plates

• Molten rock around the Earth’s core heats up the mantle above

• Currents of molten rock rise up through the mantle like boiling water

• As each current hits the underneath of the crustal plates, it starts to spread out

• This slowly pushes or tears the crust apart

Crustal PlatesCrustal Plates

• The plates are always on the move

• There are three basic types of plate boundaries – where they are sliding past each other– where plates are separating– where they are converging (approaching

each other)

Crustal PlatesCrustal Plates

• Spreading Center - the boundary between separating plates– Usually found in mid-ocean and are marked by

rugged mountain chains called mid-ocean ridges

• As plates move apart a gap continuously opens between them

• Molten rock from the earth’s interior flows into this gap – New crust is continuously formed

Plates and Sea Floor SpreadingPlates and Sea Floor Spreading

Crustal PlatesCrustal Plates

• When plates collide, the force can fold and thrust upward to form mountains

• Or the force can push the ocean floor downward to form a deep valley called a trench

• Here, molten rock can break through the seabed to form chains of islands like the Hawaiian Islands

The Mariana TrenchThe Mariana Trench

The San Andreas FaultThe San Andreas Fault

Crustal Plate ActivityCrustal Plate Activity

Crustal plate activity can…• Cause earthquakes, volcanic activity, and

tsunamis• Earthquakes are signs of the great

stresses and which affect the Earth’s crust• Over a million earthquakes occur every

year• Tsunamis are giant tidal waves and can

travel at 500 mph!

• Dinosaur Fossil bones have been found in many different parts of the world– Further supports Wegener’s single

continent theory

• The dinosaurs disappeared suddenly

– Different theories as to why– Most widely accepted is the Big Bang Theory

• Scientists theorize that a meteor hit the Earth at nearly the speed of light (186,000 miles per second!)

• Caused a total black out of the sun

• This meteor is believed to have caused the Gulf of Mexico

Gulf of MexicoGulf of Mexico

• The Earth weighs about 6000 million million million tons

• Two-thirds of the earth is covered by water

• It would take more than 250 days to walk around the equator

• Every year, North America and Europe separate by 3/4ths of an inch

• Scientists predict that life on Earth will only last 50 million more years

Earth = Onion Earth = Onion

• Crust – outermost layer, solid rock, but very thin like skin

• Mantle – denser and heavier than the crust, inner part of the mantle is described as “plastic” because it is semi-liquid rock

• Core – outer part is made of molten liquid rock that is very dense and heavy, “core” of the core becomes solid and even more dense

• Forms when rocks deep under the Earth’s crust melt

• Heat from friction as the rocks rub together can also form magma

• In places where the Earth’s crust is weak, magma wells up on the surface as volcanoes or lava flows

• As it cools, it becomes solid forming new rock

• Igneous Rock – formed form cooled magma

• Sedimentary Rock – formed by the combining together of broken bits of other rocks or sediments

• Metamorphic Rock – changed by extreme pressure or heat

• Contain complex chemicals called minerals

• Kinds of Minerals + Size of Crystals = how the rock was Formed

• Small crystals = rapid cooling

• Large crystals = more lengthy cooling

Ring of FireRing of Fire

Mount St. HelenMount St. Helen

Krakatoa, IndonesiaKrakatoa, Indonesia

• Volcanic eruption was heard 3,000 miles away

• Caused great tidal wave that killed perhaps 36,000 people

• Crystals from the magma are smaller because they cooled quickly

Crater Lake, OregonCrater Lake, Oregon

• The caldera has filled creating one of the deepest lakes

• It may erupt again

• Made by the action of water and wind as they laid down like layers of a cake

• Pressure increases and they are warmed by the heat from deep in the Earth

• Sediment becomes a solid mass of rock

Arbuckle MountainsArbuckle Mountains

Sandstone Limestone

Decaying Plant Material

Peat

Coal

• Sea Creature dies and sinks to the sea bed

• The soft body slowly decays creating oil with a layer of gas sitting on top

• Skeleton is covered in layers of mud which gradually become solid rock

• Sea bed rises above sea level• Erosion moves rock covering fossils so

they are now exposed on land

• Radio-active carbon found in all living things

• Begins to break down after an animal or plant dies

• By measuring the amount of Carbon – 14 in a fossil, scientists can tell how old it is

• This is called Carbon Dating

• Layer of air surrounding the Earth

• Consists of different kinds and amounts of gases– Nitrogen, Oxygen, Carbon Dioxide

• Protects the Earth’s surface– Filters out harmful radiation from the sun– Insulates Earth and stops the sun’s heat from

escaping back into space

Three Main Layers1) Ionosphere

• Extends about 50 miles above the surface• Rarified air• Temperature gradually rises as you move

away from the Earth

2) Stratosphere

• Extends about 30 miles above the Earth’s surface

• Contains very little air or water vapor

• Colder than Ionosphere, but warmer than the Troposphere

3) Troposphere

• Bottom layer

• About 10 miles thick

• Contains nearly all the atmosphere’s air, water vapor, and clouds

• Temperature gradually drops until is reaches the stratosphere

• Warm air…– Lighter and less dense than cold air– Rises up into the atmosphere– Produces low pressure

• Cold air…– Presses down heavily on the Earth’s surface– Produces high pressure

Cirrus– Thin, curly, and wispy

shapes – Formed in the upper

Troposphere– Contain ice crystals

Cumulus– Heaped clusters like

loose cotton balls– Have flat bases and

dome shaped tops– Sometimes build up

into thunder clouds

Stratus– Formed when

Cumulus clouds group together to form a continuous layer

– Grayer in color than Cumulus

– Bottom of the Stratus layer is in the lower Troposphere

A Meteorologist Measures…A Meteorologist Measures…

• Air pressure

• Temperature

• Humidity

• Winds speeds and directions

• Precipitation (rain, hail, snow, sleet, fog)

• Cloud types and their heights

• Visibility

– Name used in Asia– Like a tornado and

hurricane combined– Rapidly rotating tunnel

of air– Moves over land– Can be 300 miles in

diameter– Winds speed at more

than 125 mph

• Similar to cyclones, but much smaller

• Sometimes only a mile or so across

The name given to a cyclone which develops in the western Atlantic Ocean

Infancy

Youth

Maturity

Old Age

Alps Rocky Mountains

Arbuckle Mountains Cumberland Mountains

Colorado RiverYellowstone River

Rio Grande Red River