Unit 3: A2 Geography: Plate Tectonics and Associated Harzards

Alfred [blank_start]Wegener[blank_end] came up with a theory in [blank_start]1912[blank_end] that 300 million years ago there was one single continent known as [blank_start]Pangaea[blank_end]. He stated that this continent then split into two continents known as [blank_start]Laurasia[blank_end] and Gondwanaland. Today's continents were formed from further splitting of the two continents. He named this theory [blank_start]Continental Drift[blank_end] and supported his theory with several pieces of evidence.

[blank_start]Convection Currents[blank_end] rise to the Earth's core. As they reach the [blank_start]lithosphere[blank_end] they cool and spread. This drags the plates above them causing a new crust to form. As the earth never increases is size some plates are destroyed. This occurs when one plate [blank_start]subducts[blank_end] under the other. This process is known as [blank_start]subduction[blank_end]

Which pieces of evidence were used by Alfred Wegener to prove the Continental Drift Theory?

Who used sonar on the Atlantic Ocean floor and noticed it wasn't the deepest in the centre, helping identify the Mid Atlantic Ridge?

[blank_start]Maurice Ewing[blank_end] used sonar on the Atlantic Ocean floor to help identify the Mid Atlantic Ridge in [blank_start]1948[blank_end]. 14 years later in [blank_start]1962[blank_end] a geologist named [blank_start]Harry Hess[blank_end] noticed that younger rocks wear nearer to the Mid Atlantic Ridge and older rocks further away. He concluded that the sea floor was spreading from the ridge by up to [blank_start]5cm[blank_end] per year. [blank_start]Fred Vine[blank_end] knew that iron minerals within rocks align themselves with the earth's magnetic field. Every [blank_start]300,000[blank_end] years the poles reverse causing new rocks to flip direction. This resulted in a symmetrical pattern of different facing rocks on either side of the ridge.