Continents may have risen earlier than thought

[Panich52]

When Earth’s continents rose above its oceans
Jul 19, 2015
by Tom Edathikunnel in » Earth, Science Wire

Earth’s thick continental crust – the land under our feet – may have risen from the oceans half a billion years earlier than scientists previously thought.

New research surrounding the formation of Earth’s continents suggest that the buoyant terrestrial crust on which we live rose above Earth’s oceans over 3 billion years ago – half a billion years earlier than previously thought – and might be linked to the onset of the planet’s plate tectonics. Published in June, 2015 Nature Geoscience, these researchers analyzed the geochemical data from over 13,000 samples of rocks from both ocean crust and continental crust to arrive at these conclusions. Some of these samples were more than 4 billion years old.

Earth is the only known planet in the solar system with continents and wide ocean basins. The continents rise about 2.5 miles (4 km) above the ocean floor. Composed of more buoyant materials than seafloor crust, they’re an average about 21 miles (35 km) deep, in contrast to about 4 miles (7 km) thick for the crust below the oceans. Most people recognize seven continents – from largest to smallest, Asia, Africa, North America, South America, Antarctica, Europe, and Australia – but sometimes Europe and Asia are considered one continent, called Eurasia.

We today know a lot about Earth’s crust; for example, we know it is subject to continuous tectonic activity, whereby great land plates (both continental and oceanic) move slowly over our world’s underlying mantle.

But we still know very little about the earliest days of continents. Exactly when the continents formed, and how they formed, remains controversial. Previous studies had suggested that the crust surfaced within the past 2.5 billion years. This newest study – led by geochemist Bruno Dhuime of the University of Bristol in England – used an analysis of radioactive decay to shift the time at which the continents arose 500 million years earlier.

More
http://earthsky.org/earth/when-earths-continents-rose-above-its-oceans?utm_source=EarthSky+News&utm_campaign=9e46f4f119-EarthSky_News&utm_medium=email&utm_term=0_c643945d79-9e46f4f119-393525109

[6chars]

1. too much yeast?

i crack myself up.

[Flying Squirrel]

2. Why is Europe the only one that doesn't start with "A"?

Enquiring minds want to know!