Appalachians and Andes once met.

• Position: Geological research

The Appalachian Mountains probably once connected with the Andes Mountains and stretched all the way from Canada to Antarctica. lan Dalziel, a geophysicist at The University of Texas at Austin, indicates that an analysis of uplifted ocean floor and fossils from the two continents suggests that the Appalachians in the eastern U.S. and the Andes of the western South American continent at one time were the same mountain range.

Dalziel and his colleagues--Luis Dalla Salda, Carlos Cingolani, and Ricardo Varela of the University of La Plata, Argentina--assert that the Appalachian and Andean margins were aligned during the Paleozoic Eon, which extended from 550,000,000 years ago to 200,000,000 years ago, and that the two continents drifted apart millions of years before the supercontinent Pangea existed. "I should point out, however, that the Andes themselves are younger, so it's really the remnants of an old mountain belt that are in the present-day Andes," Dalziel explains. "This was all before Pangea, and that's an important part of it."

Geologists know from studies of plate motions of the Earth's crust that a supercontinent once existed which comprised the present-day continents. However, the supercontinent must have been assembled during the late Paleozoic Eon about 300,000,000 years ago, and the lack of structural evidence makes it difficult to trace the earlier continental movements. "It appears, according to our hypothesis, that eastern North America and western South America broke away from each other approximately 550,000,000 years ago, and then came back and collided again in a sort of sideswipe collision about 450,000,000 years ago. Then they drifted apart again...