Continental drift: an idea before its time Alfred Wegener Proposed idea of Continental Drift Continental drift hypothesis Supercontinent (one) called Pangaea began breaking apart about 200 million years ago Continents broke apart and then "drifted" to present positions

Fossil Evidence Both Mesosarus and Glossopteris were organisms that would not of been able to travel to the different continents at the distances that the continents are at today.

Glossopteris

Mesosaurus

Mesosaurus

Wegener’s matching of mountain ranges on different continents

Paleoclimatic (Ancient Climate) evidence

Glacial Striations

Glacial Remnants

Pangaea approximately 200 million years ago

Pangaea Breakup To view this animation, click “View” and then “Slide Show” on the top navigation bar.

Why was Wegener rejected? People couldn’t observe the plates moving The main objection to Wegener's proposal was its inability to provide a correct mechanism because he did not know about the structure of the Earth In other words, he couldn’t explain HOW and WHY the continents drift. Wegner did not have a good reason for the driving force of movement of the plates. He claimed it was the same forces that influence tides (gravity).

Harry Hess USS Cape Johnson During the war, Harry Hess discovered that the ocean floor was not smooth like everyone assumed but had: Canyons, trenches, crevasses, and volcanic seamounts

In the 1950’s, oceanographers discovered that: The largest and most extensive mountain chain on Earth was mostly underwater

The Earth seemed to be splitting apart at the seams People were surprised at how large the Mid-Atlantic Ridge was: Drilling machines took core samples, which showed that: Rocks were young at the mid- Atlantic ridge but became older as you moved away from it Glomar Challenger

Harry Hess realized that: New ocean crust was being formed on either side of the ridge and was then pushed away from it as new crust came along behind This process became known as: Sea-floor Spreading

Ocean Rocks lasted only: as long as it took them to travel to shore Hess was ignored for this idea

Sea-floor spreading animation

Other researchers found : Magnetic stripes in ocean-floor rocks. Magnetic particles in molten rock line up in the direction of Earth’s magnetic poles. The Magnetic Poles of the Earth flip-flop When rock hardens, a permanent record of Earth’s magnetism remains in the rocks.

Magnetic Reversal Animation

2 men from Cambridge drew all the strands together: In 1963 they used magnetic studies to prove Hess’s theory Suggested that this meant the continents were moving too Most scientists finally accept the theory in 1964 and agree to call pieces of moving crust “plates” Some geologists still rejected the idea into the 1980’s

Why is magnetic reversal strong evidence for sea-floor spreading? Lets do an activity – each table group will need: 2 colored pencils (2 different colors) 1 manila folder with a slit cut into it 1 piece of paper Some tape Scissors

Sea Floor Spreading classroom activity Cut your piece of paper in half lengthwise so you have 2 long, skinny pieces. Tape the shorter ends of your two pieces of paper together like this: Paper 1 Paper 2 Tape

Fold the two papers at the tape line Spread the manila folder over the sink so the slit is above the sink and tape it into place on the desk. Feed the taped end of the paper through the slit of the folder. Push it through until you have about an inch of the free ends sticking out of the folder. Two group members will grab one of the free ends of the paper sticking out of the folder. The 3rd member will have the colored pencils ready.

7) Upon the teacher’s instructions, you will begin to SLOWLY pulling your hands apart (while holding onto the paper) until you hear “STOP”. 8) The third member will take 1 color and color in the paper that is now pulled out of the center slit. 9) We will repeat steps 7 & 8 several times, switching colors after each stop to represent the flipping of the Magnetic Poles.

Analysis Complete the questions on the back of yesterday’s note sheet.