Harry Hess and Robert Dietz said this spreading does not make the Earth bigger. As new ocean floor is created, an equal amount is destroyed.

BOB DOUGHTY: The two scientists said Alfred Wegener was correct. The continents do move as new material from the center of the Earth rises, hardens and pushes older pieces of the Earth away from each other. The continents are moving all the time, although we cannot feel it.

They called their theory “sea floor spreading.” The theory explains that as the sea floor spreads, the tectonic plates are pushed and pulled in different directions.

FAITH LAPIDUS: Diamonds produced deep within the Earth have helped scientists learn when the continents first started moving. A report on the diamonds was published last July in the journal Science.

American and South African researchers studied more than four thousand four hundred diamonds from five continents. The researchers say mineral grains trapped inside the diamonds provided information about the Earth’s mantle. They say changes in the chemical structure of the grains suggest that the process called plate tectonics began between three and three point two billion years ago.

(MUSIC)

FAITH LAPIDUS:The idea of plate tectonics explains volcanoes as well as earthquakes. Many of the world’s volcanoes are found at the edges of plates, where geologic activity is intense. The large number of volcanoes around the Pacific plate has earned this area the name “Ring of Fire.”