Continents shifted around at far slower than a snail’s pace throughout Earth’s history like pieces of a puzzle, drifting together and pulling apart to form oceans, he said. Part of the eventual fascination with his idea came from globe-gazers’ observation that continents such as Africa and South America look like they could fit together snugly.
Following up on Wegener and others’ work, a University of North Carolina at Chapel Hill geologist believes he has discovered a new, long-vanished supercontinent. That early amalgamation of most of the world's continents in one vast land area later split up several times, reformed and divided again to begin shaping Earth’s current continents.
The primeval supercontinent, which Professor John J.W. Rogers named Columbia, existed more than 1.5 billion years ago and is older than any of several giant landmasses previously proposed.
“I named the supercontinent Columbia because some of the best evidence for its existence is in the Columbia River region of western North America,” Rogers said. “Starting at about 1.8 billion years ago, all of the continents existing at that time began to collide into a single land area.”
Rogers describes his ideas in a scientific paper with fellow geologist Dr. M. Santosh of Kochi University in Japan published in the current issue of the Gondwana Research, a quarterly journal devoted to studies of Earth’s early land masses.
The east coast of India became attached to western North America, with southern Australia against western Canada, he said. Most of present South America rotated so that the western edge of Brazil lined up with eastern North America, forming a continental margin that extended into the southern edge of Scandinavia.
“This formed an area that stretched about 8,000 miles from southern South America to northern Canada and was about 3,000 miles across at its widest part,” Rogers said.
Columbia began to break up about 1.5 billion years ago, and its fragments moved around the Earth independently for several hundred million years, he said. About a billion years ago, the fragments came together again to form a new supercontinent, called Rodinia. Rodinia lasted until about 700 million years ago before it too broke into several fragments.
These chunks moved independently until 250 million years ago, when the supercontinent Pangea formed, Rogers said. Pangea then began to break up almost immediately to form the world's present continents.
“This sequence of formation and dispersal of supercontinents is clearly caused by movements deep within the Earth in a layer scientists call the mantle,” he said. “The exact mechanism is still being worked out, and hopefully the discovery of Columbia will contribute to understanding it.”
Magnetic and geologic evidence for supercontinents becomes less certain and more controversial as the age of the supercontinent increases, Rogers said. For that reason, the shape of Columbia and even its existence is less certain than that of Rodinia.
Originally trained as petrologist and geochemist, the UNC scientist came up with his ideas while traveling in the Orkney Islands off Scotland’s north coast. He based them on data he collected in India, East Africa and Saudi Arabia as U.S. leader of a joint Indian and U.S. cooperative study of the Precambrian evolution of southern India and on data published by other scientists.
Geologists date ancient rocks by measuring radioactive decay of uranium and lead isotopes. Comparisons of such information and rock types around the world reveal what regions used to be connected.
Rogers served as guest editor of the special issue, much of which is devoted to papers by other authors evaluating the proposed Columbia supercontinent and related information. The International Association for Gondwana Research, based in Kochi, Japan, publishes the journal.
Note: Rogers can be reached at (919) 942-2609 (h), 962-2581 (w) or jrogers@email.unc.edu Contact: David Williamson, 962-8596
By DAVID WILLIAMSON
UNC News Services
Journal
Gondwana Research