Plate Tectonics Chapter 17

The Earth’s Drifting Continents German scientist Alfred Wegener, 1900’s proposed the Theory of Continental Drift It was widely disputed, 30 years after his death, enough evidence was collected to support his theory German scientist Alfred Wegener, 1900’s proposed the Theory of Continental Drift It was widely disputed, 30 years after his death, enough evidence was collected to support his theory

Evidence Glossopteris, located in 250 myo rocks, were found in South Africa, Australia, India, and Antarctica Antarctica once had a warmer climate Rock formations and deposits lined up on several continents Evidence of glaciers in now warm climates Glossopteris, located in 250 myo rocks, were found in South Africa, Australia, India, and Antarctica Antarctica once had a warmer climate Rock formations and deposits lined up on several continents Evidence of glaciers in now warm climates

The Evidence

The Real Issue……….. How could the continents move through the solid rock bottoms of the oceans? In the 1950’s, scientists using better instruments found underwater mountain chains with rift valleys in their centers How could the continents move through the solid rock bottoms of the oceans? In the 1950’s, scientists using better instruments found underwater mountain chains with rift valleys in their centers

Midocean ridge

Earth’s Spreading Ocean Floor Midocean ridges form the single largest mountain range in the world 80,000 km long and 3 km high Lava erupts to form new sea floor and spread As it spreads it takes continents with it This explained the mechanism for continental drift! Midocean ridges form the single largest mountain range in the world 80,000 km long and 3 km high Lava erupts to form new sea floor and spread As it spreads it takes continents with it This explained the mechanism for continental drift!

Magnetic stripes on the ocean floor were further evidence that the sea floor was spreading The patterns are identical on each side of the ridge Closer examination shows that the magnetic poles have reversed themselves nine times in the past 3.5 million years Magnetic stripes on the ocean floor were further evidence that the sea floor was spreading The patterns are identical on each side of the ridge Closer examination shows that the magnetic poles have reversed themselves nine times in the past 3.5 million years

Iceland, "the land of fire and ice", is being split by an oceanic ridge that surfaces to create an oceanic island in the North Atlantic Ocean. Red triangles show Iceland's active volcanoes, including Krafla. Reykjavik is Iceland's capital.

If the ocean floor is being created, is the Earth getting bigger? Rock in the ocean is relatively young Ocean floor is being destroyed in trenches in a process called subduction The denser ocean crust is pushed downward into the mantle and melts Rock in the ocean is relatively young Ocean floor is being destroyed in trenches in a process called subduction The denser ocean crust is pushed downward into the mantle and melts

The Earth’s Moving Plates The Theory of Plate Tectonics, which links continental drift and seafloor spreading, explains how the Earth has evolved over time. It helps to explain the formation, movement, collisions, and destruction of the Earth’s crust

Lithospheric Plates There are seven major plates, Pacific, North American, South American, Eurasian, African, Indo-Australian, and Antarctic There are many small plates, Caribbean, Arabian are examples Each plate moves at a different speed and direction Some are oceanic and some are continental There are seven major plates, Pacific, North American, South American, Eurasian, African, Indo-Australian, and Antarctic There are many small plates, Caribbean, Arabian are examples Each plate moves at a different speed and direction Some are oceanic and some are continental

Plate Boundaries Divergent boundary- plates moving apart

Convergent boundary- plates that are moving together

Transform boundary, slip-strike, lateral faults- plates slide past one another

Tectonic Humor

More About Our Moving Earth

Plate Motion The power of the convection currents in the mantle is thought to be the force that moves the plates

Collision of Continental and Oceanic Plates

Collision of Continental Plates

Collision of Oceanic Plates

Will the Earth Continue to Change?

The Earth’s Changing Surface Stress is what causes the surface of the Earth to change As the rocks undergo stress, they slowly change shape and volume They also move up and down or sideways Stress is what causes the surface of the Earth to change As the rocks undergo stress, they slowly change shape and volume They also move up and down or sideways

Types of Stresses Compression squeezes the rock Tension causes the rocks to stretch out over a larger area Shearing of the rock causes it to twist or tear Compression squeezes the rock Tension causes the rocks to stretch out over a larger area Shearing of the rock causes it to twist or tear

Faulting A break or a crack along which rocks move Earthquakes are sometimes along these faults A break or a crack along which rocks move Earthquakes are sometimes along these faults

Faulted Mountains and Valleys Mountains formed when there are many normal faults in one area Blocks of rock are uplifted Valleys may form when the block of land between 2 normal faults slides downward Mountains formed when there are many normal faults in one area Blocks of rock are uplifted Valleys may form when the block of land between 2 normal faults slides downward

Folded Mountains When stress is applied to the rock formation and it bends but doesn’t break Forms an anticline which is an upward fold and a syncline which is a downward fold When stress is applied to the rock formation and it bends but doesn’t break Forms an anticline which is an upward fold and a syncline which is a downward fold

Volcanic Mountains Single peak mountains formed from volcanoes

The Floating Crust Isostasy is the balance between the downward force of the crust and the upward force of the mantle

Peaceful changes!!!!!!