Ancient Sea Floor Discovery

7 04 2007

Scientists have found evidence of plate tectonics in an ancient sea floor in Greenland dating back nearly 4 billion years.

A report, published in the journal Science, says the outcrop in Greenland’s Isua Belt shows the earliest evidence of plate tectonics –the geological theory used to explain large-scale motions of the Earth’s shell, the BBC said.The discovery pushes back the Earth’s geology timeline by 1.3 billion years.

Isua

 

The rocks are found in the Isua Belt, in southwest Greenland

The baked and twisted rocks, now part of Greenland, show the earliest evidence of plate tectonics, colossal movements of the planet’s outer shell. The unique find, described in the journal Science, shows the movements started soon after the planet formed.

“Since the plate tectonic paradigm is the framework in which we interpret all modern-day geology, it is important to know how far back in time it operated,” said Professor Minik Rosing of the University of Copenhagen and one of the authors of the paper. “Sea floor is not normally preserved for more than 200 million years.”

The rocks analyzed in Greenland are found in an area known as the Isua Belt, a zone of intensely deformed rocks in the southwest of the island that geologists have pored over for decades.

The ophiolite structure was mapped between outcrops covering 4-5km (2.5-3 miles) and shows the correct sequence of layers found in an ophiolite, except the lowest mantle portion.

“You can actually recognize features that formed in a couple of minutes, 3.8 billion years ago – a quarter of all time – and you can actually go and touch them with your hand,” said Professor Rosing.

pillow lava

 

Ancient pillow lavas are preserved in exquisite detail

In particular, the discovery pushes back the oldest known evidence of plate tectonics by at least 1.3 billion years and gives scientists clues to the processes that formed the surface of the Earth today.

Although the structures and processes that led to their formation would be similar to the modern era, they would not be exactly the same. The young Earth was much hotter than now, and as it shed heat, it put many of the tectonic processes into overdrive.

The rate of recycling of oceanic crust would therefore have been even quicker than today, making the fact that the rocks in Isua are preserved at all even more extraordinary.

“These fragments are extremely rare,” said Professor Rosing. “It’s just very exciting when you get one of these glimpses when you can look back nearly four billion years in time.”

PLATE TECTONICSPlate tectonics graphic

  • Magma rises from the asthenosphere at mid-ocean ridges
  • New crust cools and spreads away from ridge
  • Denser oceanic crust begins to sink back into the mantle at subduction zone
  • Melting of slab creates volcanoes on overlying continental crust

By Jonathan Fildes
Science and technology reporter, BBC News

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