Bangladesh officials warned Thursday that an oil spill from a crashed tanker is threatening endangered dolphins and other wildlife in the massive Sundarbans mangrove region, branding the leak an ecological "catastrophe".

The tanker carrying an estimated 350,000 liters (75,000 gallons) of oil collided on Tuesday with another vessel and partly sank in the Sundarbans' Shela river, home to rare Irrawaddy and Ganges dolphins.

Environment ministers from around the world face mounting time pressure on Thursday to shape a blueprint for a global pact on climate change with ground-breaking carbon curbs at its core.

There are concerns over an unwieldy draft text, intended to guide negotiations that by December 2015 must forge the most ambitious environmental accord in history.

A Siberian tiger which had been freed by Russian President Vladimir Putin has returned to his homeland two months after crossing the border to China, state media said Wednesday.

Kuzya, one of three tigers released into the wild by Putin, arrived back on his native soil Tuesday, the official Xinhua news agency reported, citing the Forestry Department of northeast China's Heilongjiang province.

NASA says a newly spotted 1,300-foot (400-meter) wide asteroid is not a threat to hit Earth, despite recent media reports.

NASA's Near Earth Object program manager Donald Yeomans said the asteroid, discovered in October by Russian scientists, won't even get that close to Earth in the next 150 years. And it isn't a threat to any other planet, either.

Canada will only impose regulations to cut carbon emissions from its oil and gas sector -- its top source of emissions -- if and when the United States moves to do the same, the prime minister said Tuesday.

"We want to see oil and gas regulations on a continental basis given the integrated nature of this industry," Prime Minister Stephen Harper said in the House of Commons.

Green groups hoped for a big turnout at a protest in Lima Wednesday aimed at heaping pressure on ministers haggling over a post-2020 deal to curb carbon emissions.

The "People's Climate March" in the Peruvian capital follows mobilization on the eve of the September 23 summit in New York that revived climate change as a political priority.

A mountain on Mars may have built up over time from lake sediments, according to NASA scientists who have been studying observations from the Curiosity rover scouring the Red Planet.

The latest analysis is based on rocks discovered at the lower edges of Mount Sharp, which is located, rather oddly, in the midst of a crater on Earth's neighboring planet.

A significant amount of the potent greenhouse gas methane may be leaking into the atmosphere from abandoned oil and gas wells, according to a study in Pennsylvania out Monday.

The study in the Proceedings of the National Academy of Sciences is based on direct measurements of methane outflow from and near 19 abandoned oil and gas wells in the northeastern U.S. state.

Scientists in a lab used a powerful laser to re-create what might have been the original spark of life on Earth.

The researchers zapped clay and a chemical soup with the laser to simulate the energy of a speeding asteroid smashing into the planet. They ended up creating what can be considered crucial pieces of the building blocks of life.

The slaughter of Africa's elephants and the illegal trade in ivory in China are "out of control" and could push wild elephants extinction within a generation, conservationists said Tuesday.

Soaring quantities of ivory are being sold in rapidly growing numbers of shops in China, with over 100,000 elephants killed from 2010 to 2012, the joint report read from the campaign groups Save the Elephants and The Aspinall Foundation.