Age of Ocean Rocks and Sediments

The cross-geological formation was a major discovery, to the theory of continental drift. However, due to the continual changing rock-formation process, geologists were unable to establish which formations matched. To resolve this problem, they tried to match up similar age and rock types.  

To determine the exact age of a rock, scientists used the method of radiometric dating. They found that rocks towards the edges of mid-ocean ridges are younger than those further in from the margins. Before this, scientists were unfamiliar with what happened on the ocean floors. Until, various research vessels discovered huge undersea ridges across the floors of the oceans. It was then that they understood that new ocean crust was continually being created.

By 1965, oceanographers Maurice Ewing and Bruce Heezen had shown that various ocean ridges were connected as a vast water mountain range around the globe. Then in the early 1960's the idea of seafloor spreading was established. The idea suggested that heat currents deep within the planet were continuously changing the surface of the earth and was the force that allowed the continents to separate.  This idea helped Wegener to explain how the continents may have moved, which, as mentioned in an earlier blog, was the biggest problem with understanding his theory. (Sea-floor spreading animation: The animation helped me understand how mid-ocean ridges are formed by sea-floor spreading.)

When the age of sea-floor rocks are mapped out, it can be easily seen how some continents match up. The best match is between the continents Africa and South America. As shown in the picture there is some similarity between the ages of rocks especially about 550 million years old, which once again suggests that the continents were once joined together.

Another addition to this, is the pattern of sediments on the sea floor near the ridges. If the oceans were very old and unchanging, the ocean floors should be level and covered in layers- the oldest at the bottom and the youngest at the top. However, oceanographers have found that the sediments are thickest near the continents and there are little or no sediment at the mid-ocean ridge. Therefore, contributes to how the ages of rocks are older as they move further away from the ridge. The picture helps demonstrate the layering of sediments on the ocean floor.