Most genetic changes in humans occurred in past 5000 years, finds new study

Subodh Varma, TNN Nov 29, 2012, 02.55PM IST

NEW DELHI: In the past 5000 years, the human genome - the genetic code carried in our DNA - has accumulated a large number of variations, many of them potentially harmful. This has happened because of exploding human population, which causes naturally arising genetic mutations (changes) to keep collecting and getting passed on to progeny.
A study published today in the scientific journal Naturehas detailed when many of those rare variants arose. The study had a fairly large sample of 4,298 North Americans of European descent and 2,217 African Americans which enabled the researchers to gather unprecedented details from the genetic code. Study co-author Josh Akey, a genomics expert at the University of Washington in Seattle told Nature that the researchers now have "a way to look at recent human history in a way that we couldn't before."

Mercury's north pole has ice, Nasa spacecraft discovers

AP | Nov 30, 2012, 02.15 AM IST

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Mercury's north pole has ice, Nasa spacecraft discovers

Scientists announced that the orbiting probe, Messenger, has found evidence of frozen water, even though Mercury is the closest planet to the Sun.

CAPE CANAVERAL (Florida): Just in time for Christmas, scientists have confirmed a vast amount of ice at the north pole on Mercury, the closest planet to the Sun.

The findings are from Nasa's Mercury-orbiting probe, Messenger, and the subject of three scientific papers released Thursday by the journal Science.

The frozen water is located in regions of Mercury's north pole that always are in shadows, essentially impact craters. It's believed the south pole harbors ice as well, though there are no hard data to support it. Messenger orbits much closer to the north pole than the south.

"If you add it all up, you have on the order of 100 billion to 1 trillion metric tons of ice," said David Lawrence of the Applied Physics Laboratory at Johns Hopkins University. "The uncertainty on that number is just how deep it goes."

The ice is thought to be at least 1.5 feet (0.5 meters) deep and possibly as much as 65 feet (19.8 meters) deep.

There's enough polar ice at Mercury, in fact, to bury an area the size of Washington, D.C., by two to 2.5 miles (4 kilometers) deep, said Lawrence, the lead author of one of the papers.

"These are very exciting results," he added at a news conference.

For two decades, radar measurements taken from Earth have suggested the presence of ice at Mercury's poles. Now scientists know for sure, thanks to Messenger, the first spacecraft to orbit Mercury.

The water almost certainly came from impacting comets, or possibly asteroids. Ice is found at the surface, as well as buried beneath a dark material, likely organic.

Messenger was launched in 2004 and went into orbit around the planet 1{ years ago. Nasa hopes to continue observations well into next year.

Columbia University's Sean Solomon, principal scientist for Messenger, stressed that no one is suggesting that Mercury might hold evidence of life, given the presence of water. But the latest findings may help explain some of the early chapters of the book of life elsewhere in the solar system, he said.

"Mercury is becoming an object of astrobiological interest, where it wasn't much of one before," Solomon said.

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Most genetic changes in humans occurred in past 5000 years, finds new study

Mercury's north pole has ice, Nasa spacecraft discovers

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