- Geomorphology– the study of landforms of the earth’s surface
- Plate tectonics– a theory explaining the structure of the earth’s crust and many associated phenomena as resulting from the interaction of the rigid lithosphere.
- Geomorphological hazard– an event causing harm to people or property, caused by Geomorphological processes such as plate tectonic movement.
Francis Bacon 1620
- As far back as 1620, Francis Bacon spotted that the west coast of Africa and the east coast of South America looked as if they would fit together, like pieces of a jigsaw puzzle. Between then and 1912 other people identified further similarities between other continental coastlines.
Robert Mallet 1870s
- Robert Mallet was a nineteenth century scientist who managed to measure the speed at which earthquakes spread.
Alfred Wegner 1911
- While at Marburg, in the autumn of 1911, Wegener was browsing in the university library when he came across a scientific paper that listed fossils of identical plants and animals found on opposite sides of the Atlantic.
- Intrigued by this information, Wegener began to look for, and find, more cases of similar organisms separated by great oceans.
- Orthodox science at the time explained such cases by postulating that land bridges, now sunken, had once connected far-flung continents.
- However, Wegener noticed the close fit between the coastlines of Africa and South America. Might the similarities among organisms be due, not to land bridges, but to the continents having been joined together at one time? As he later wrote: “A conviction of the fundamental soundness of the idea took root in my mind.”
- Such an insight, to be accepted, would require large amounts of supporting evidence. Wegener found that large-scale geological features on separated continents often matched very closely when the continents were brought together.
- For example, the Appalachian Mountains of eastern North America matched with the Scottish Highlands, and the distinctive rock strata of the Karroo system of South Africa were identical to those of the Santa Catarina system in Brazil.
- Wegener also found that the fossils found in a certain place often indicated a climate utterly different from the climate of today, for example, fossils of tropical plants, such as ferns and cycads, are found today on the Arctic island of Spitsbergen.
- All these facts supported Wegener’s theory of “continental drift. “In 1915 the first edition of The Origin of Continents and Oceans, a book outlining Wegener’s theory, was published; expanded editions were published in 1920, 1922, and 1929.
- About 300 million years ago, claimed Wegener, the continents had formed a single mass, called Pangaea from the Greek for “all the Earth”. Pangaea had rifted, or split, and its pieces had been moving away from each other ever since.
- Wegener was not the first to suggest that the continents had once been connected, but he was the first to present extensive evidence from several fields known as Mesosaurus fossils.
1948 Ewing
- The discovery and study of the Mid-Atlantic ridge. In 1948, Ewing noted the presence of a continuous mountain range extending the whole length of the ocean bed, volcanic rocks of recent age.
- His primary sources of evidence included the fit of the continents, glacial till deposits, and the apparent shifting of climatic belts over time.
- Wegener noticed that the continents seemed to fit together, not at the continuously changing shoreline, but at the edge to their continental shelves.
- He derived this hypothesis from the observation that the continents in the southern hemisphere exhibit an identical pattern of rock and fossils known as the “Gondwana sequence”.
- The most logical explanation was that the continents themselves were once parts of a much larger “super-continent” which was named Pangaea. Wegener collected ancient climate information to confirm his glacial data.
- For the glaciers to have been present with the continents in their current positions, much of the world should have been under ice.
- But this wasn’t the case. Sedimentary rock examination showed a change in climates, and the only possible explanations were continental drift or movement of the poles. One source of evidence was that of Palaeomagnetism.
- When hot magma rises to the earth’s surface and cools, the minerals themselves especially magnetite become magnetized in alignment with the Earth’s magnetic field. Rocks that were formed at different places on the Earth’s surface have different magnetizations.
- Using this information, when rock layers were uncovered with a magnetization that did not agree with its position on the Earth, questions were raised. It was proposed that the Earth’s magnetic poles wandered.