Earth history 1
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Transcript of Earth history 1
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
http:
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• The plates move slowly on the upper mantle (asthenosphere)
http:
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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
http:
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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
http:
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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