EARTH HISTORY 1:

Geological Changes

ppt. by Robin D. Seamon

• Earth is dynamic (changing)• Heat from the center • Energy from the Sun

INSIDE:• Decay of radioactive isotopes• The release of this heat causes:

• churning of the molten rock inside• Release of heat through cracks/vents in the crust

• Convection causes plates of crust to move about

OUTSIDE:• Sun’s Energy on the atmosphere and water make:

• Wind • Currents• Evaporation- Water Cycle

• This causes weather & larger patterns of climate

• It influences Water Cycle which controls weathering, erosion, & deposition

http://www2.mps.mpg.de/projects/sun-climate/se_body.html

INSIDE• 99% of rock inside the Earth is greater than 2,000˚F(radioactive decay generates the heat)

• Crust: (0.2 – 1.1 % crust or 4-43 miles deep) 700˚F- 1,500˚F

• Mantle: (45 % interior) hot magma 7,000˚F

• Core: (54% of interior) Fe, Ni 10,000˚F

COMPOSITION:

• Scientists study earthquake waves to determine what’s inside

• Pattern of waves through the Earth shows something dense in the center

• Fe (iron) fits this description & also explains magnetic field

http://www.indiana.edu/~geol105/images/gaia_chapter_3/seismic.htm

• Geothermal: relating to heat inside the earth

DEEPEST man-made hole:• Kola Superdeep

borehole- NW Russia• 40,000 ft & then too

hot to dig more

Crust 21 miles deep in Baltic Region

At 7.4 miles, 300˚F

Average oil well is ~ 1

mile

Scientists try to harness this geothermal Energy for renewable Energy source

OUTSIDE• Plate Tectonics: plates move about ½” to 3” a year• Theory that the Earth’s lithosphere is composed of 10+ plates

that fit together like a puzzle

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• The plates move slowly on the upper mantle (asthenosphere)

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• Movement is caused by convection inside the Earth• Hot goes up, cold goes down- • plates are along for the ride

• Continental Drift: in the 1900’s scientists realized the plates were moving, but didn’t know why

• Volcanoes: sometimes the heat can escape through vents at the surface; magma & hot gases from inside are released until pressure is abated

• Largest- Mauna Loa, Hawaii 18,000square miles• Big eruptions occur several times/Century

• Shield volcano: layers of lavareleased from non-explosive eruptions (Mauna Kea, Hawaii)

• Cinder cone volcano: pyroclastic material- dust & ash explodes out (Paracutin, Mexico)

Composite volcano: pyroclastic explosions followed by slower, longer flowing-lava (Mt. St. Helens

• Earthquakes: tension builds up at plate boundaries until the plates slip & tension is released- we feel earthquakes

Tsunami: when earthquake happens under the ocean

EVIDENCE in CRUST

• Uplift: places on the crust that bulge upwards because of pressure underneath

• can help predict future earthquakes or eruptions

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http://bc.outcrop.org/GEOL_B10/lecture18.html

• Predicts tension at a divergent boundary

• Predicts loss of material below

• Subsidence: places on the crust that are sinking down in elevation

• Rebound: places on the crust that rise in elevation when a heavy weight is removed

• Ice sheet melts• During droughts when water table is emptied• Heavy building is removed

http://bprc.osu.edu/education/rr/webex/WebExGridLinks2Pg6.html

FAULTS & BOUNDARIES

• Compression: two plates are pushed together at convergent boundaries

Results in:• Folding (crust folds into mountains)• Faulting (crust pushes up or falls in block mountains)• Subduction (cooler oceanic crust goes beneath

warmer continental crust)• earthquakes

ADVANCE

Folded Mountains

http://freddoty.com/folded-mountains

near the Sullivan River in the Canadian Rockies

The Cape Fold Belt Mountains 

http://www.geocaching.com/geocache/GC2CEJP_steytlerville-arch?guid=ff36205a-b979-422c-8266-f7f83ec4d884BACK

BACK

Fault-block Mountains

Nepal

BACK

Subduction

http://www.uoguelph.ca/geology/geol2250/glossary/HTML%20files/subduction.html

• Tension : two plates are pulled apart at divergent boundaries

Results in:• Sea-floor spreading (new sea floor is made)• Trenches or rifts (gashes made from the pulling apart)• Subsidence or faulting• earthquakes

Thingvellir Breach, Iceland

• Shear : two plates slide past each other horizontally in a transform boundary

Results in:• Ridges• earthquakes

San Andreas Fault, Ca

ROCK CYCLE

• Rock Cycle: process by which new crust is continually being recycled

At plate boundaries:-pull apart (making new crust)-push together (forming mountains) -subduct (under other plates)

http://www.perfecthomepictures.com/277773-gabbro-igneous-intrusive-phaneritic

PROCESSES:1. crystallization2. heat & pressure3. weathering/erosion/deposition4. Compaction/cementation5. Melting

ACTIVITY LINK http://www.passmyexams.co.uk/GCSE/physics/rock-cycle.html

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• Igneous rock: rock formed from cooling magma• Intrusive igneous: crystalizes inside the earth slowly (hot in

there) making larger crystals• Extrusive igneous: crystalizes fast outside the earth (cooler)

making fewer crystals

INTRUSIVE EXTRUSIVE

granite gabbro basalt obsidian

• Metamorphic rock: rock is under heat & pressure for a long time so that it chemically changes into another type of rock

granite

gneiss

sandstone

quartzite

slate

shist

coal

diamond

• Sedimentary rock: rock is formed over time by sediments being compacted together

• Hold fossils that describe Earth’s early life forms• The strata (layers) help determine relative age of rock

Clay sediment makes shale

Sand sediment makes sandstone

Mineral deposits in water make limestone

Dead plants & animals make fossil fuels

Gravel, shell, & fossils make

conglomerate

HOW OLD IS THE EARTH?

• Age of the Earth has been debated for Centuries

TRADITIONAL VIEW:• At first scientists thought that the Earth was formed & has

been cooling ever since (not true)… led to wrong numbers• They thought the earth was static & that only catastrophes led

to changes• We now know earth has a heating mechanism inside causing

changes in the shape of the crust!

Despite these incorrect numbers, geologists had some correct ideas too:• Nicolas Steno 1660’s studied sedimentary rocks

Relative Dating• Law of Superposition: said that sediment layers (strata) are deposited in a time sequence: oldest on bottom, youngest on top

http://www.angelfire.com/az3/mohgameil/physical.html

• Unconformity places where no sediments were preserved (erosion) for a time; separates different ages

Angular unconformity

Grand Canyon, Arizona

• Principle of original horizonality: said that layers of sediment are originally deposited horizontally

• (therefore if they aren’t, something moved them after they were laid down)

• Principle of cross-cutting relationships: says that a feature is younger than the feature it cuts across

• William Smith 1790’s • Hypothesized that if two layers of rock at different

locations contain similar fossils, then rocks must be the same age

• Index fossils: fossils used to determine relative age of rocks

NEW CONTROVERSIAL IDEAS: 1800’s

• Charles Lyell 1830• geologist who said the Earth’s features

were constantly changing & therefore Earth was much older than previously thought

• (PEOPLE DID NOT LIKE IT)

• Uniformitarians: changes were constant and uniform: processes at work in the past are still occurring today

MODERN DATING METHODS

1900 Radioactivity discovered (unstable atoms)

Absolute Dating• Radiometric dating using radioactive forms of elements in rock

to determine the age of the rock or fossil

How it works:• Atoms in an element have the SAME number of protons• Sometimes their number of neutrons is different: isotopes• Radioactive: unstable isotopes break down (decay) over time• Decay happens at steady rate for each element • Half-life: time it takes for ½ of the sample to decay (scientists

know for each element)• Compare amount of parent isotope to daughter isotope to know

age of rock/fossil

Amount Parent isotope

Amount Daughter isotope

AGE OF ROCK/FOSSIL

Common types: Potassium-Argon(> 1000,000 ya)

Uranium-Lead(> 10 million ya)

Rubidium-Stronium(>10 million ya)

Carbon-14 (in fossils)

• If rock becomes molten, radioactivity escapes & we can’t determine age

• Rock Cycle???• How old is the Earth?• We use-

• Samples from Earth (oldest Zircon crystal found so far in Australia)

• Samples from meteorites that hit Earth• Samples from the moon• Date the Sun based upon luminosity & Energy as

compared to other stars• Ice core data…

… So most scientists agree that with current technology, the Earth is…

4.5 billion years old