Mountainous Yemen is blessed with more water than its Arabian desert neighbors but the national passion for the stimulant plant qat threatens to exhaust that precious resource.

In the mountains around Sanaa, farmers are drilling so many unlicensed boreholes to irrigate the thirsty crop -- craved by the capital's residents --that the water table is falling by as much as six meters (20 feet) a year.

The world's oldest and best-preserved sperm, dating back 17 million years, has been unearthed in Australia, scientists said Wednesday.

The sperm from an ancient species of tiny shrimp was discovered at the Riversleigh World Heritage Fossil Site, an area in the far north of the state of Queensland where many extraordinary prehistoric Australian animals have previously been found.

Three astronauts, including a Russian and an American, touched down safely on Earth Wednesday aboard a Soyuz capsule, the first such landing since Russia's relationship with the West slumped amid the Ukraine crisis.

The returning crew consisted of Japan's Koichi Wakata, who was the first ever Japanese commander of an ISS space mission, as well as NASA astronaut Rick Mastracchio and Russian cosmonaut Mikhail Tyurin.

The next time your throat is as dry as a bone and the Sun is beating down, take a glass of clean, cool water.

Savour it. Sip by sip.

German and Danish scientists on Monday said they had identified dozens of chemicals, including some used in hygiene and consumer products, that interfere with male fertility by damaging sperm.

Writing in the journal EMBO Reports, the team said a third of 96 compounds they tested using a new technique had an adverse effect on sperm.

British satellite operator Inmarsat said Monday it was offering a basic tracking service to all the world's passenger airlines free of charge, following the disappearance of Malaysian Airways flight MH370.

Inmarsat, which has played a role in the search for the missing plane, said the service it was offering would provide definitive positional information.

Ice is melting in the western Antarctic at an "unstoppable" pace, scientists said Monday, warning that the discovery holds major consequences for global sea level rise in the coming decades.

The speedy melting means that prior calculations of sea level rise worldwide made by the Intergovernmental Panel on Climate Change will have to be adjusted upwards, scientists told reporters. 

Scientists on Sunday said that methane which leaked from the 2010 oil-rig blowout in the Gulf of Mexico persisted in the sea for months beyond a presumed cleanup of the gas by marine microbes.

As much as half a million tonnes of natural gas, 80 percent of it methane, leaked into the deep sea as a result of the blowout on April 20, 2010, on BP's Deepwater Horizon rig.

Scientists on Sunday said they had used a harmless electrical current to modify sleep so that an individual has "lucid dreams," a particularly powerful form of dreaming.

The discovery provides insights into the mechanism of dreaming -- an area that has fascinated thinkers for millennia -- and may one day help treat mental illness and post-trauma nightmares, they said.

The global cost of securing a clean energy future is rising by the year, the International Energy Agency (IEA) warned Monday, estimating that an additional $44 trillion of investment was needed to meet 2050 carbon reduction targets.

Releasing its biennial "Energy Technology Perspectives" report in Seoul, the agency said electricity would increasingly power the world's economies in the decades to come, rivaling oil as the dominant energy carrier.