Chapter 7.2 Restless Continents pgs. 173-176 10-01-14 IN: How did scientists come up with the idea that the lithosphere is broken into tectonic plates?

Restless Continents

Wegener’s Theory Inspired by the puzzle-like fit of the continents Alfred Wegener developed the theory in the early 1900s Continental drift is the theory that continents can drift apart from one another and have done so in the past.

What is Wegener’s Evidence? 1.) Fossils of the same plant (glossopteris) and animal species (mesosaurus) are found on both sides of the Atlantic Ocean.

What is Wegener’s Evidence? 2.) Geological Evidence: Similar types of rock and evidence of the same ancient mountain formations were found on several continents.

What is Wegener’s Evidence? 3.) Evidence of Climate Change: Glacial grooves in rocks on different continents created by receding glaciers that match and are in the same direction.

Pangaea Wegener thought that 245 mya all the separate continents of today were joined in a single landmass the he called Pangaea and a single ocean called Panthalassa .

Pangaea About 180 mya it began to break into two main pieces. The northern half is known as Laurasia, the southern is known as Gondwanaland.

Pangaea About 65 mya, around the time the dinosaurs went extinct, they broke into many pieces and looked not too different from what the continents look like today.

What he didn’t know Wegener could not explain what force could move the continents. He died in 1930 in an expedition to Greenland.

The Theory of Continental Drift Died with Alfred Wegener!!! OUT: Name three pieces of evidence Wegener used to explain his theory.

The Theory of Plate Tectonics Section 7.2 (Part II) The Theory of Plate Tectonics states that the lithosphere is divided into tectonic plates that move around on the asthenosphere. It was developed in the 1950s and 60s and replaces Alfred’s theory

New Evidence New technology from World War II such as submarines, the ability to test the age of rocks and sonar helped scientists revive Alfred’s ideas.

Mid-Ocean Ridge Underwater mountain chains that run through Earth’s ocean basins.

Mid-Atlantic Ridge Ships with sonar began to map the ocean floor, and a undersea mountain chain was discovered. 1.)Mid-Ocean Ridges are volcanic and are where sea-floor spreading occurs.

Sea-floor Spreading The process by which new oceanic lithosphere is created as older materials are pulled away. The youngest crust is closest to the MOR, and the oldest is near the continents.

Rifts This also happens on land creating “Rift valleys”

Magnetic Reversal 2.) Magnetic Reversals, or paleomagnetism, is when Earth’s magnetic poles change place.

This happens 4-5 times every million years

Tracking Plate Motion 3.) Satellites like GPS track the movement of the plates. The plates move centimeters per year.

OUT: Name three pieces of evidence used to describe the Theory of Plate Tectonics.