The Earth in the Universe - How the Earth is Changing

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The theory of plate tectonics is now well established. Continental drift is happening as tectonic plates move, with earthquakes and volcanoes often occuring around their edges.

Evidence from Rocks

Rocks provide evidence for changes in the Earth. In 1785 James Hutton presented his idea of a rock cycle to the Royal Society. He detailed ideas of erosion and sedimentation taking place over long periods of time, making massive changes to the Earth’s surface. Geologists can use other evidence from the rocks themselves such as: looking at cross-cutting features (rock that cuts across another is younger), using fossils (species existed/ became extinct during certain time periods) and deepness of the rock (younger rocks are usually on top of older ones). This kind of evidence only shows that some rocks are older than others. To get a more accurate idea of the age of rocks radioactive dating is used.

Wegener's Theory

Alfred Wegener proposed the theory of continental drift at the beginning of the 20th century. His idea was that the Earth's continents were once joined together, but gradually moved apart over millions of years. It offered an explanation of the existence of similar fossils and rocks on continents that are far apart from each other. But it took a long time for the idea to become accepted by other scientists.

Before Wegener

Before Wegener developed his theory, it was thought that mountains formed because the Earth was cooling down, and in doing so contracted. This was believed to form wrinkles, or mountains, in the Earth's crust. If the


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