New theory of continent formation - Johns Hopkins Univ researcher Bruce Marsh postulates that large crystals found in cooling magma are transported from great depths - Brief Article

USA Today (Society for the Advancement of Education), June, 1997

There are major flaws in conventional beliefs about the process that formed and continues to shape the continents, maintains Bruce Marsh, professor of earth and planetary sciences, Johns Hopkins University. The process in which molten rock, or magma, migrates to the planet's surface in meandering columns of molten mush is more involved than geologists had thought.

The pea-sized crystals that appear in solidified magma deposits settle to the floors of the molten deposits, distilling and enriching the magma and allowing it to form the material from which the continents eventually are produced. The larger the crystals, the more the magma is enriched. Geologists had postulated that these crystals grew and collected, as a sort of precipitate, in the cooling magma, but Marsh's findings have led him to a much different explanation.

The large crystals actually were transported from great depths by the columns of molten slurry, he has concluded. After discovering that detail about the origin of the crystals, he was able to use the golden-green stones as tracers, tracking the chemical and physical path that the magma took as it flowed up to the surface in Antarctica.

Over millions of years, molten rock surged up from deep reservoirs, forming and pushing apart the continents, ultimately making it possible for higher, terrestrial animals to evolve. The fulminating magma also might have played a vital role in the beginning of life on the primeval Earth, as the most primitive organisms congregated around hydrothermal vents on ocean floors.

Marsh likens the siphoning of crystals in magma to domestic plumbing. "If somebody is working on the pipes of your house and you turn on the faucet hard, you get sand, junk. If you turn on the faucet just a little bit, you don't get any of that junk." Similarly, fast-flowing magma pulls up large, older crystals, grown long before the specific eruptive event that brought them to the surface. For about a century, those old crystals have been misidentified as new crystals, formed after the magma has come to rest, but the newer crystals are actually much smaller, about the diameter of a hair or thin thread. "This has confused us for 100 years, making us think that magmas chemically change and build continents in ways that they don't."

Geologists long had adhered to the idea that the magma was injected, as if with a syringe, from its deep source to the Earth's surface. They assumed no crystals were present during the trip. Marsh, though, has found that the mushy magma is not injected to the surface -- it actually is pushed up through a series of chambers, picking up crystals of various sizes along the way and depositing those crystals in pools that solidify. Like the slow-moving water in the domestic-plumbing analogy, the magma was not flowing with enough force to drag the older crystal debris to the surface.