QUICK REVIEW… Layers of the Earth Crust (2 types) Mantle Outer Core Inner Core Earth’s crust & the very top solid portion of the mantle form the lithosphere The lithosphere sits on top of the liquid asthenosphere

LAW OF UNIFORMITARIANISM Law of Uniformitarianism: States that Earth is an always changing place The same forces of change are at work today that were at work in the past. Some changes are gradual; some changes are fast…some times both!

TECTONIC PLATES The Lithosphere is broken into many large and small slabs of rock called tectonic plates and where two plates meet, a lot of changes can occur.

How do the tectonic plates move? The plates move because of convection currents. The hot, soft rock in the mantle rises…then it cools, and sinks. How do the tectonic plates move?

There are 3 types of plate boundaries TECTONIC PLATES 1. Divergent 2. Convergent 3. Transform There are 3 types of plate boundaries

SUBDUCTION What is SUBduction? When one tectonic plate sinks under another plate IT CAN ONLY HAPPEN WHEN… Continental & oceanic plate collide = oceanic plate ALWAYS sinks because it is more DENSE. Oceanic & oceanic plate collide = the more dense plate sinks! What is SUBduction?

DIVERGENT

DIVERGENT Mid-ocean Ridges Rift Valleys Earthquakes Volcanoes What occurs at this boundary? New Crust Forms Mid-ocean Ridges Rift Valleys Earthquakes Volcanoes

CONVERGENT: CONTINENTAL-CONTINENTAL

CONVERGENT: CONTINENTAL-CONTINENTAL What occurs at this boundary? High mountains Earthquakes

CONVERGENT: OCEANIC-OCEANIC

CONVERGENT: OCEANIC-OCEANIC What occurs at this boundary? Deep-ocean Trenches Volcanic Islands Earthquakes Hawaii is NOT on a plate boundary!

CONVERGENT: OCEANIC- CONTINENTAL

CONVERGENT: OCEANIC-CONTINENTAL What occurs at this boundary? Deep-ocean trenches Coastal mountains (some are volcanic) Earthquakes

TRANSFORM

TRANSFORM What occurs at this boundary? Faults Earthquakes

PANGAEA Scientist Alfred Wegener noticed that Earth’s continents seemed to fit together like a puzzle, so he hypothesized that they were once joined in a single “super continent” called Pangaea which means “all land”

CONTINENTAL DRIFT This led to his Theory of Continental Drift – that although the continents were once joined, they slowly drifted apart! But nobody believed him …why? Wegener’s Evidence: 1. Matching rock layers on different continents 2. Matching fossils on different continents 3. Evidence of climate change – tropical plant fossils in cold places, ice scratches in warm places

SEA FLOOR SPREADING The sea floor spreads apart at divergent boundaries allowing new crust to form…this new crust builds Mid-Ocean ridges The crust closest to the crack is the youngest while the crust further from the crack is older

MAGNETIC REVERSALS Minerals in the magma that rise through the cracks in the sea floor align themselves with Earth’s magnetic poles (North and South) As the rock cools, the minerals stay fixed in this position, like a compass Earth’s poles periodically reverse. The “stripes” of rock along the ocean floor record these reversals.