Magazine article Science News

New View Surfaces of Ancient Atlantic

Magazine article Science News

New View Surfaces of Ancient Atlantic

Article excerpt

New view surfaces of ancient Atlantic

Most geologists blieve an ocean similar in size to the North Atlantic occupied that same general area about 500 million years ago. A British geologiest now suggests this ocean looked not like the open body of water that today separates Europe from North America, but instead like a smaller version of the island-dotted sea between Southeast Asia and Australia.

This cluttered sea would have flanked a larger ocean to the south, says Roger Mason of University College in London. Although other geologists accept Mason's geographic analogy, few appear to agree with the small size he proposes for the North Atlantic's ancient predecessor.

Mason's evidence for a smaller northern sea rests on Scandinavian rocks previously identified as ocean-floor fragments. These rocks derive from the bases of volcanic islands formed atop oceanic crust and not from the bottom of a wide ocean, he says. According to plate-tectonic theory the oceanic crustal plate carrying the islands would have disappeared gradually beneath thicker continental crust, eventually rafting the islands into collision with the continent and depositing the once-submerged rocks on what is now the west coast of Norway. In the September GEOLOGY, Mason contends the Norwegian rocks do not possess the full sequence of minerals and mineral-grain sizes associated with deposits in large oceans.

Paleomagnetic data -- which indicate where rocks form in relation to the Earth's magnetic poles -- constitute another pillar of Mason's argument. He admits models based on these data can be risky, but, his report asserts, sediment and fauna patterns along the North Sea and the English Channel also point to the past existence of a smaller sea north of a larger ocean.

Mason's conclusions contradict many models holding that the North Atlantic precursor, often called lapetus, was similar in size to its southern neighbor. …

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