Plate Project

Caitlynn Brown

Seafloor Spreading

Evidence -

young/old rocks-

They found the young rocks closer to the mid-ocean ridge because the magma hardens here, and they found the older rocks closer to the continents because they are being pushed away.

magnetic pole reversals-

Magnetic energy switches from N to S as it goes away from the mid-ocean ridge.

Evidence -

The theory was that hot, less dense material( liquid) below Earth's crust rises toward the surface at mid-ocean ridges. Then it flows sideways, carrying the seafloor away from the ridge in both directions.

The seafloor spreads apart and magma is forced upwards and flows through the cracks. Then it cools and forms new seafloor.

Seafloor Spreading Document

Summary of Seafloor Spreading

Seafloor spreading is when magma comes up between the oceanic crust in the mid-ocean ridge and cools down, leaving new sea floor. This new sea floor pushes the old seafloor out towards the continents. Then the oceanic crust moves under the continental crust and begins to melt into magma. Where this happens is called the subduction zone. Harry Hess hypothesized the act of seafloor spreading, and unlike Alfred Wegener, Hess had evidence to support his hypothesis. Some evidence that supported Hess's hypothesis were young and old rocks, and magnetic reversals. The young rocks are near the mid-ocean ridge because they were just created by the cooled magma, and the older rocks are closer to the continents because when new seafloor is made it pushes the rest of the seafloor outwards. Magnetic reversals is when the magnetic energy changes from North to South as the sea floor spreads out.

Seafloor Spreading Statement

I think seafloor spreading is a valid hypothesis. There is good evidence supporting seafloor spreading such as the young/old rocks, and the magnetic pole reversals. The Glomar Challenger found that the youngest rocks are near the mid-ocean ridge, which support Harry Hess' hypothesis. Also scientists have found that the direction the rocks are pointing change every so often.

Continental Drift

Continental Drift

Animal Fossils -

Fossils of the Mesosaurus have been found on both South America and Africa. They figured that it probably couldn't swim between the continents(saltwater) because it was a fresh water animal, so it is hypothesized that the continents were all one landmass at some point.

Plant Fossils -

The Glossopteris plant fossil is found on many different continents. Because it's found on so many continents it helps for the conclusion of all the continents being one large landmass. (similar climates)

Climate -

Fossils of warm weather plants were found in colder places.

Glaciers deposits have been found on many continents (temperate and tropical climates too), this means they once had glaciers.

Rock Segments -

Certain rock types were found on the coasts where the continents were once believed to be connected, which supports the hypothesis.

Continental Drift Summary

Alfred Wegener came up with the idea that the continents were once one large landmass. Many of you did not believe him and may have thought of him as crazy, but now here is some evidence that what he said was true. Scientists have now discovered the fossils of a Mesosaurus on both South America and Africa, but this animal was a freshwater animal. So, scientists believe that there is no way it could have swam between the two continents in a saltwater ocean. Also, glacier deposits have been found in tropical areas, which means there were once glaciers on other continents. Another piece of evidence is that the same type of rock layers are on the coasts of continents where they were believed to be connected at some point. And last but not least, scientists discovered a plant fossil, the Glossopteris, on many different continents. This means that the continents had to have similar climates at one point in time. So now, with all this new evidence, you will accept Alfred Wegeners' theory that the continents were once all one large landmass, and that they slowly drifted apart.

Continental Drift Statement

I believe the hypothesis of continental drift is not necessarily true. Most of the evidence of continental drift can be debunked or some of it like the rock segments could be purely coincidental.

Plate Tectonics

Plate Tectonics Statement

I believe that the plate tectonic theory is valid. And it would make sense that at convergent boundaries there are mountains, volcanoes, etc, since they collide. Divergent boundaries make rift valleys because they separate It also makes sense that transform boundaries can cause earthquakes since the plates slide past each other.