Earth history 1

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Information about Earth history 1

Published on September 23, 2014

Author: seamonr



Earth's surface has changed in its long history and continues to change via the same processes

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 View slide

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 View slide

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 _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

• The plates move slowly on the upper mantle (asthenosphere) volcanic-activity-and-Earths

• 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 lava released 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

• Subsidence: places on the crust that are sinking down in elevation • Predicts tension at a divergent boundary • Predicts loss of material below

• 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

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 near the Sullivan River in the Canadian Rockies The Cape Fold Belt Mountains BACK

BACK Fault-block Mountains Nepal

BACK Subduction

• 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)

PROCESSES: 1. crystallization 2. heat & pressure 3. weathering/erosion/deposition 4. Compaction/cementation 5. Melting ACTIVITY LINK

• 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 granite gabbro basalt obsidian INTRUSIVE EXTRUSIVE

• 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

• 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

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