How can we prove plate tectonics? LO: evaluate scientific evidence Starter: what is happening in the...

How can we prove plate tectonics?

LO: evaluate scientific evidenceStarter: what is happening in the image?

Good Judgement-what info do I need?

1. In the beginning

• Each culture has its own Creation myth and the Christian view of the world being created in 7 Days was accepted in many parts of the world.

• In the 17th century Archbishop Ussher worked out that the world was made in 4004 BC by adding up the ages of the descendants of Adam in the Bible.


https://www.youtube.com/watch?v=_Ge5mD938K0

2. Hutton’s Unconformity

• Geologists started to have doubts about this as it seemed that the time needed for rocks to form was immense.

• They saw that some rocks had fossils in them which were land animals and some were marine.

• Sometimes they came across places where one rock was dumped on top of another-called an unconformity.

• In the 18th century a Scottish geologist, called James Hutton, wrote about these phenomena and proposed that the processes that we see today, like erosion and deposition, happened in the past.

• These processes were slow, so it must have taken a long time for rock layers to be made.


3. Fossils

• Rocks of the same type and age had the same kinds of fossils in them.

• So geologists knew there was a sequence of rocks, but didn’t know their age.


4. Radioactive Dating

• Scientists argued about the age of the planet until Ernest Rutherford ( a New Zealand born physicist) showed that rocks contain radioactive elements (like Uranium).

• In 1904 he gave a talk to the Royal Institution in London where he showed that these radioactive elements “decayed” or lost their radio-activity over time.

• So, if you could measure the level of radiation in a rock, you could work out how long ago it was formed.

• Using this method the age of the Earth has been measured to around 4.6 billion years.



5. Jigsaw

• When more accurate maps of the world were being created in the 19th century several people noticed that the continents of Africa and South America looked like they fitted together.

Antonio Snider-Pellegrini's Illustration of the closed and opened Atlantic Ocean (1858).


6. Wegener• In 1912 a German meteorologist

called Alfred Wegener made a presentation outlining what he called “Continental drift”

• He matched up fossils and rock types from different continents and proposed that they were all joined together in the past.

• His ideas were rejected by most scientists because he couldn’t explain how this might have happened.


7. Paleo-Magnetism

• Iron in volcanic rocks like basalt records the direction of the Earth’s magnetic field when they were formed.

• By studying thousands of rock samples in the 1950s, it was shown that the basalt rocks of Greenland had moved 15o since they were formed. Other studies from around the world showed that other places had moved too.

• Was Wegener right after all? Good Judgement-what info do I need?

8. Sea Floor Spreading

In 1955 British scientist Ron Mason manages to measure the magnetism of the Pacific Ocean floor by trailing an instrument after an ocean going ship the USS Explorer.He was surprised to find a striking zebra pattern-some rocks had magnetism that pointed South, others pointed North.People realised that this showed that the Earth’s magnetic field had flipped in the past.Then they realised that each stripe showed the same age of rocks.The youngest were near the centre of the ocean, and the oldest near the edge.


9.Hawaiian Islands

• Hawaiin legend said that Pele the goddess of volcanoes once lived on the most westerly of the islands, but had been forced to move eastward several times after being attacked by her sister.

• They recognised that the west islands were older.• Canadian geologist Tuzo Wilson proposed that there was

a weak spot in the earth’s crust at Hawaii. As the seafloor moved westward over this point, volcanoes would form.

• As the seafloor continued to move, the heat supply for the volcanoes would be lost and they would become extinct


10. Seismic activity

• In the 1960s the US wanted to record whether the Russians were testing nuclear weapons, so set up a global set of instruments to record them.

• They also recorded earthquakes.• When these earthquakes were mapped, most were

concentrated in thin strips.


11. Final pieces

• Studies of the 1964 Alaskan earthquake showed that land near the sea had risen. This was linked to the oceanic trench off the coast.

• The crust of the ocean was sliding under the continent

• Studies of the gases produced by volcanoes shows that it contains elements of marine life and seawater

• Mountain ranges like the Himalayas are still rising• Using GPS to measure plate movement• Convection currents in the mantle



http://www.youtube.com/watch?v=Q6UObH0xxZU

http://www.unavco.org/community_science/science-support/crustal_motion/dxdt/model.html

Summary

• Geological time • Fossils• Dating of rocks• Continental Drift-jigsaw• Magnetism• Hawaii• Earthquakes• Barnacles and gases• GPS

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How can we prove Plate Tectonics?

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