Earth Formation, Earth Layers, & Plate Tectonics Earth’s beginning: Most accepted scientific theory dates the Earth at _4.6_ billion years old. Scientists determined the age of Earth by dating Precambrian zircon crystals in rocks at _4.4 _ billion years old, moon rocks at __4.45_ billion years old, and meteorites which range from _4.5_ – _4.7_billion years old

The early Earth was a hot, molten ball Sources of internal heat: 1. Gravitational Contraction: as Earth’s mass grew, gravity caused the mechanical energy of contraction to be converted to thermal energy. 2. Radioactive Isotopes released (and still do release) thermal energy as the isotopes go through radioactive decay. 3. Bombardment by Asteroids and Meteors also caused mechanical energy to be converted into thermal energy . http://channel.nationalgeographic.com/videos/the-birth-of-earth/ (2 ½ minute video on Earth’s birth)

As Earth cooled, crust formed as its upper layer solidified. These early crust pieces returned to the mantle carrying water which when recycled produced a less dense, granitic crust. Differentiation: Layering of the Earth as it cooled due to differences in density, (iron sank) while Earth was still in a molten phase. First water & atmosphere: As earth cooled the raw materials for water and an atmosphere emerged due to geologic activities (i.e. volcanoes, geysers, rifts, trenches, etc.) + comets & meteors. https://www.youtube.com/watch?v=YrruvHNwGq4 (10½ minute video: Earth's formation and history)

Earth’s Layers Two things increase the closer to the center of the Earth (core) we go: Density: mass per unit volume. (how closely packed matter is in a space) 2. Temperature: (It gets Hotter!!!) Main layers of the Earth: Crust Mantle Outer Core Inner Core

The Crust (Lithosphere) Solid: Made up of Silicates. (very light material) Oceanic crust is more dense (Basaltic). Continental crust is less dense (Granitic). 8-40 km thick. Temperature increases at 1ºC per 40 m after 1st 20 m

The Mantle Middle, semi-solid hot rock layer; composed of mostly silicates, but is also rich in iron and magnesium which makes it more dense than the crust. It has Plasticity; which is the ability of a solid to flow. 2900 km thick Asthenosphere – upper layer that the lithosphere floats on. Mesosphere – the lower layer Temperature ranges from 870 ºC - 2200 ºC https://www.youtube.com/watch?v=Kpoko_l34ZE (1 minute convection video)

The Core: center of Earth Outer Core – liquid 2250 km thick 2200 ºC – 3200 ºC Inner Core – solid due to extreme pressure 1300 km thick 3200 ºC – 5500 ºC

Plate Tectonics If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle. In 1910, Alfred Wegener’s proposed Continental Drift: the hypothesis that Earth’s plates are floating on the mantle in a slow & steady motion caused by convection currents. Pangaea– the name given to the single land mass that split and moved apart about 200 mya to form today’s continents. (means all lands) https://www.youtube.com/watch?v=nuzJYiYT39A (Continental Drift video: 1 ½ min.) https://www.youtube.com/watch?v=2It3ETk2MGA (future drift video: 1 minute)

Evidence for continental drift and Pangaea Landforms – shape of continental coastlines, mountain ranges, coal fields, etc. Fossils – same plant & animal fossils on continents now separated by water. Climate – tropical plant fossils in cold climates today {Spitsbergen Norway & Antarctica} & glacier tracks in rocks in warm climates today {Africa, S.A., Australia & India} 4. Magnetic reversal of polarity stripes in rocks in the ocean floor crust. Satellite & Sonar data

Plate Tectonics: The earth’s crust is divided into tectonic plates which move in various directions.

3 Types of Plate Boundaries: 1. Divergent Boundary: plates move apart creating new crust (rift valley & mid-ocean ridge) ← →

2. Convergent Boundary: plates collide and destroy or buckle crust (move together) → ← Oceanic-Oceanic: subduction of one plate under another creating trenches & volcanic islands Oceanic-Continental: oceanic (more dense) subducts under continental (less dense) creating trenches & volcanic mountains. Continental-Continental: compression and buckling forms tall folded mountains.

3. Transform Boundary: plates sliding side-to-side (creates faults & earthquakes) ↑↓ https://www.classzone.com/books/earth_science/terc/content/visualizations/es0804/es0804page01.cfm?chapter_no=visualization (plate boundaries animation)

Sea-Floor Spreading

- The mid-ocean ridge is the longest chain of mountains in the world - The mid-ocean ridge is the longest chain of mountains in the world. - Scientists mapped the mid-ocean ridge using sonar. - At the mid-ocean ridge, molten material rises from the mantle and erupts. The molten material spreads out, pushing older rock to both sides of the ridge. - Youngest rocks in the ocean are at the mid-ocean ridge; and the oldest are at the trench in the subduction zone. - Sea-Floor Spreading is the process where the new crust is formed at the mid-ocean ridge and destroyed at deep ocean trenches melting back into the mantle. CHECK THIS OUT!!

Evidence for Sea Floor Spreading New material is erupting along the mid-ocean ridge. The presence of pillow shaped rocks has showed that molten material has erupted again and again. Oceanic rocks shows that Earth’s magnetic poles have reversed; iron bits lined up in the opposite direction. Drilling into the sea floor shows the youngest rock closer to the mid-ocean ridge; the older rock are farther away.

Ridge push occurs when new crust forms at the mid-ocean ridge and pushes older crust away Slab pull occurs when a slab of old crust gets pulled down by gravity at the trench

The processes of subduction and sea-floor spreading can change the size and shape of the oceans. Because of this process, the ocean floor is renewed about every 200 million years.

The Pacific Ocean is shrinking at an average of 9 cm/year (3½ inches) The Pacific Ocean is shrinking at an average of 9 cm/year (3½ inches)! This is due to the fact that a deep-ocean trench is swallowing more crust than the mid-ocean ridge can produce. The Atlantic Ocean is expanding an average of 2.3 cm/year (1 inch)