Scientist Timeline

• Continental drift
• Mid Ocean Ridges
• Sea-Floor Spreading
• Pangaea
• Plate Tectonics

Continental drift - the lateral movement of continents resulting from the motion of crustal plates. - Alfred Wegener

Mid ocean ridges - any of several seismically active submarine mountain ranges that extend through the Atlantic, Indian, and South Pacific oceans: each is hypothesized to be the locus of seafloor spreading. - Harry Hess

Sea-Floor Spreading - a process in which new ocean floor is created as molten material from the earth's mantle rises in margins between plates or ridges and spreads out - Harry Hess

Pangaea - the hypothetical landmass that existed when all continents were joined, from about 300 to 200 million years ago. - Abraham Ortelius

Plate Tectonics - a theory of global tectonics in which the lithosphere is divided into a number of crustal plates, each of which moves on the plastic asthenosphere more or less independently to collide with, slide under, or move past adjacent plates. - Harry Hess

Abraham Ortelius - As early as 1596, the Dutch map maker Abraham Ortelius suggested that the Americas, Eurasia and Africa were once joined and have since drifted apart "by earthquakes and floods" His "evidence" was the jigsaw fit of the continents. His theory helped the other scientists.

Alfred Wegener - proposed the theory of continental drift in 1912, after noticing that there were similar glacial deposits in the southern continents, which had a rational distribution if these continents were once joined. The theory also helped explain the distribution of fossils, living plant and animal species and the occurrence of matching rock types in continents that were once contiguous.

Wegener's theory was not accepted by the scientific community of the day, as there was little evidence to reveal the processes which drove the movements of the continents.The theory was discredited for decades until the 1960s, but, with a growing body of evidence to support both the movement of the continents and the mechanisms which drive the movement, the theory is now widely accepted.

Harry Hammond Hess - a professor of geology at Princeton University, was very influential in setting the stage for the emerging plate-tectonics theory in the early 1960s. He believed in many of the observations Wegener used in defending his theory of continental drift, but he had very different views about large-scale movements of the Earth. Wegener, he was able to see his seafloor-spreading hypothesis largely accepted and confirmed as knowledge of the ocean floor increased dramatically during his lifetime.