Plate Tectonics The Earth’s top layer
The Earth’s top layer, the lithosphere is divided into multiple patches. These patches are called plate tectonics. Plate tectonics explain the movement of the Earth’s surface from the past and present. It is an enormous, irregularly shaped slab of solid rock, that is often made up of oceanic and continental plates. The size of a tectonic plate can differ hugely, it can be a few hundreds of kilometers to thousands of kilometers. The thickness of the tectonic plate can vary depending on the age of the plate. If the plate is younger, the thickness can be 15 km or less but if the plate is much older the thickness can be 200 km or more. There is seven huge plate tectonics, these are bigger than the majority of the continents. There is a 10 or more medium sized plates and about 60 smaller plates. A lot of the larger plates are slowly breaking into many smaller plates.
Continental drift is a theory that was proposed by Alfred Wegener in 1912. The theory was that all the continents were once all joined together as one large continent. A continent of this size is known as a supercontinent. This supercontinent was known as Pangea. The observations as to why Alfred Wegener believed that all the continents were one, was that all the continents fit perfectly together like a jigsaw puzzle. Another observation that Alfred Wegener took into consideration when coming up with this theory was that fossils from the same prehistoric species and age was found in continents that were very far apart from each other. Alfred Wegener could not understand how these species managed to cross oceans to reach these places, he then believed that the animals did not move, it was the continents that had shifted over time. When Alfred Wegener proposed the theory of continental drift to other scientists did not believe that continents so big could move. Alfred Wegener died in 1930 before the new evidence could prove him correct.
In 1962 Harry Hess an American geologist wanted to explore the ocean floor during World War II when he was working for the US navy by using sonar technology (sound waves). Harry Hess found evidence that there was many flat topped mountains and mid-ocean ridges. He proposed that the theory of seafloor spreading was that new rocky crust was being formed at the ocean ridges and that it was spreading outwards. That was the process of seafloor spreading. To support his theory he used magnetic striping, the age of the seafloor and the thickness of the sediment. Harry Hess’ theory of Seafloor spreading supports Alfred Wegener’s theory of continental drift.
Magnetic striping are strips of the seafloor rock that has alternating magnetic direction. The direction of the Earth’s magnetic field changes every couple of million of years. The crystals in the rock will become attracted and change direction so that it will be facing where ever the “magnetic North” is when it begins to form on the seafloor. When the Earth’s magnetic field changes it is a process called polarity reversal. Polarity reversal causes the magnetic stripes in the seafloor rock. Tiny pieces of magnetite that is found within the volcanic basalt which makes up the seafloor behave like tiny little magnets. The tiny pieces of magnetite align themselves with the Earth’s magnetic field.