' A More Alluring Neighbor ' : Venus may have been livelier ; then its moving parts jammed.

Venus today is not like Earth. Temperatures hover around 850 degrees Fahrenheit, and clouds of sulfuric acid float around its atmosphere.

But a new study suggests that Venice may have once possessed an important Earth-like feature : plate tectonics, the constant reshaping of moving pieces of the planet's crust.

''Both planet's very likely had plate tectonics operating roughly at the same period of time,'' said Matthew B. Weller, a planetary scientist at the Lunar and Planetary Institute at Houston who led the research.

The conclusion suggests that Venus could have been much more like Earth in other ways.

The geochemical reactions associated with plate tectonics could have buried much of the carbon dioxide that makes Venus so hellish today, with those temperatures of 460 Celsius.

A few billion years ago, Venus might have been a place where life could thrive.

Dr. Weller and his colleagues found no visual signs of plate tectonics. The clue was in the air - particularly in the nitrogen content of the air. When planets like Earth and Venus form, nitrogen is locked in minerals.

But in volcanic eruptions, particularly those associated with tectonic plates pulling apart,  the mineral melt, chemical bonds break and nitrogen escapes into the atmosphere.

Using computer simulations, the scientists explored two models : plate tectonics and what is called the stagnant lid. Earth's moon and Mars have stagnant lids - solid shells of outer crust that trap most gases underneath.

Had Venus always had a stagnant lid, as it appears to have now, the models indicated that there would be less nitrogen than is observed today - 3.5 percent of the atmosphere [ Earth's air is more than three-fourths nitrogen].

The explanation that worked for current Venus conditions combined the two models : an early phase of plate tectonics that released carbon dioxide and nitrogen, followed by the crust's locking up into a stagnant lid. 

[ Kenneth Chang].


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