"Planet Earth, the living machine" and science history–main points
Study of the earth advanced in the 1790's as part of revolutions in industry, science, religion, and politics. The religious establishment had taught that the earth was created suddenly 6000 years ago, and that the oceans and continents were unmoving and unchanging. This theory of a sudden creation is called "catastrophism".

James Hutton of University of Edinburgh, Scotland, challenged this view. He said that earth was much older, and that mountains and oceans change their shapes and locations slowly over a much longer time period–"with no beginning and no end." The idea of ongoing creation, destruction, and re-shaping is called "uniformitarianism" and is now accepted. The changes are caused, Hutton said, by "Earth’s great heat engine."

Hutton lived near a dormant volcano, "Arthur’s Seat." He noticed places where one type of rock intrudes into another type, which meant that creation of land was a multi-step process. With help from others, he found areas where distinct layers were atop one another, and where lake-bottom sediment layers had hardened, then tilted to vertical, and then gotten covered by other layers, as more proof of ongoing formation of the planet.

In the early 1900's, Alfred Wegener, a German scientist, studied fossils, finding hot-weather plants and animals up near the North Pole, and evidence of glaciers near the Equator. He theorized that the continents have moved.


As further evidence, Wegener showed underground patterns indicating that a mountain range in the Eastern US is linked to one in Europe–they formed as one range, but were later split by movement of the continents. His ideas
did not catch on, because people could not accept the idea of huge continents moving, and Wegener could not say what moved them.


In 1957-58, the "International Geophysical Year" attempted to get the USA and the USSR to cooperate peacefully by doing science together.
One project was to study and map the bottoms of the oceans using several methods. This found several surprises, which helped prove Wegener’s ideas:
*The oceans are not big basins, as they appear. Instead, there are ridges in the middle of the oceans.

*These ridges are volcanic, with lava spewing out. There are bigger and more obvious cracks in the earth’s crust underwater than there are on land.

*Magnetic research by Americans Cox and Dalrymple and others confirmed that newer crust is found near the mid-ocean ridges. The cracks there are spreading, but new lava keeps hardening to form new crust near the cracks. In 1962, Britishers Vine and Matthews calculated speeds of crust movement usually around 1 inch per year. Faster speed means faster plate movement.

By the 1960s, the former USA military scientists Harry Hess and Robert Dietz proposed "seafloor spreading" as the mechanism that pushes the continents.

We now know the largest plates’ location, shape, and direction of movement. Researchers keep finding smaller plates (microplates), and evidence where small plates have crashed into big ones and joined them. These additions are called "exotic terranes" (spelling is correct) or "accretions".