News & Current Affairs

September 26, 2008

Team finds Earth’s ‘oldest rocks’

Team finds Earth’s ‘oldest rocks’

The rocks contain structures which might indicate life was present

Earth’s most ancient rocks, with an age of 4.28 billion years, have been found on the shore of Hudson Bay, Canada.

Writing in Science journal, a team reports finding that a sample of Nuvvuagittuq greenstone is 250 million years older than any rocks known.

It may even hold evidence of activity by ancient life forms.

If so, it would be the earliest evidence of life on Earth – but co-author Don Francis cautioned that this had not been established.

“The rocks contain a very special chemical signature – one that can only be found in rocks which are very, very old,” he said.

The professor of geology, who is based at McGill University in Montreal, added: “Nobody has found that signal any place else on the Earth.”

“Originally, we thought the rocks were maybe 3.8 billion years old.
The exciting thing is that we’ve seen a chemical signature that’s never been seen before
Prof Don Francis, McGill University

“Now we have pushed the Earth’s crust back by hundreds of millions of years. That’s why everyone is so excited.”

Ancient rocks act as a time capsule – offering chemical clues to help geologists solve longstanding riddles of how the Earth formed and how life arose on it.

But the majority of our planet’s early crust has already been mashed and recycled into Earth’s interior several times over by plate tectonics.

Before this study, the oldest whole rocks were from a 4.03 billion-year-old body known as the Acasta Gneiss, in Canada’s Northwest Territories.

The only things known to be older are mineral grains called zircons from Western Australia, which date back 4.36 billion years.

Date range

Professor Francis was looking for clues to the nature of the Earth’s mantle 3.8 billion years ago.

He and colleague Jonathan O’Neil, from McGill University, travelled to remote tundra on the eastern shore of Hudson Bay, in northern Quebec, to examine an outcrop of the Nuvvuagittuq greenstone belt.

The rocks turned out to be far older than first thought

They sent samples for chemical analysis to scientists at the Carnegie Institution of Washington, who dated the rocks by measuring isotopes of the rare earth elements neodymium and samarium, which decay over time at a known rate.

The oldest rocks, termed “faux amphibolite”, were dated within the range from 3.8 to 4.28 billion years old.

“4.28 billion is the figure I favour,” says Francis.

“It could be that the rock was formed 4.3 billion years ago, but then it was re-worked into another rock form 3.8bn years ago. That’s a hard distinction to draw.”

The same unit of rock contains geological structures which might only have been formed if early life forms were present on the planet, Professor Francis suggested.

Early habitat?

The material displays a banded iron formation – fine ribbon-like bands of alternating magnetite and quartz.

This feature is typical of rock precipitated in deep sea hydrothermal vents – which have been touted as potential habitats for early life on Earth.

“These ribbons could imply that 4.3 billion years ago, Earth had an ocean, with hydrothermal circulation,” said Francis.

“Now, some people believe that to make precipitation work, you also need bacteria.

“If that were true, then this would be the oldest evidence of life.

“But if I were to say that, people would yell and scream and say that there is no hard evidence.”

Fortunately, geologists have already begun looking for such evidence, in similar rocks found in Greenland, dated 3.8 billion years.

“The great thing about our find, is it will bring in people here to Lake Hudson to carry out specialised studies and see whether there was life here or not,” says Francis.

“Regardless of that, or the exact date of the rocks, the exciting thing is that we’ve seen a chemical signature that’s never been seen before. That alone makes this an exciting discovery.”

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September 6, 2008

Deadly rockslide hits Cairo homes

Deadly rockslide hits Cairo homes

People at the site of the rock slide (6/9/08)

At least 20 people have been killed by a rockslide which destroyed homes in Cairo, emergency services say.

Dozens of houses in the shanty town east of central Cairo were hit by huge boulders and rocks, reports said.

Witnesses said a six-storey building in the impoverished Duwayqa district below the Muqattam hills had been completely reduced to rubble.

Some people are believed to be still trapped in the rubble and police have cordoned off the area.

At least 20 people are reported to have been injured and the number of casualties is expected to rise.

Reports said that at least eight boulders – each estimated to weigh about 70 tonnes – had fallen from the towering cliffs overlooking the district at about 0900 local time (0700 GMT).

“It was horror,” said Hassan Ibrahim Hassan, 80, whose house escaped the destruction.

Distraught residents

“The power went out, we heard a loud bang like an earthquake and I thought this house had collapsed. I went out, I saw the whole mountain had collapsed.”

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Witnesses described seeing hundreds of distraught people gathered around the site of the destruction, saying they had relatives and friends trapped under the rubble.

Some were scrabbling at the rocks with their bare hands.

The remains of the town have been covered by a thick layer of dust.

Rescue teams were forced to wait for the arrival of cranes and heavy lifting equipment to allow them to move the huge rocks.”I couldn’t find my house this morning,” said Mustafa Abdel-Fatah. “I could only see rocks on top of everything.”

It was not clear what had triggered the rockfall but a our correspondent says there have been previous landslides in the area.

August 14, 2008

Arsenic-munching bacteria found

Arsenic-munching bacteria found

Bacteria(USGS)

Microbial biofilms form in rocky pools, fed by hot springs containing arsenic

In the warm, bubbling pools of Mono Lake in California, scientists have isolated a bacterium that fuels itself on arsenic.

Combining light and arsenic, these bacteria make their food and multiply using a chemical that is toxic to most other life forms.

The researchers think using arsenic as an energy source was a process used by ancient bacteria.

Their findings are reported in the journal Science.

Ronald Oremland of the US Geological Survey explained that these bacteria are photosynthetic, using sunlight – like plants – to turn carbon dioxide into food.

What is different about them is that instead of using water in this process, they use arsenic.

The US-based researchers isolated the bacterium from the lake, which lies at the foot of the Sierra Nevada.

Colour film

“These lakes are fed by hydrothermal waters that leach out arsenic-containing minerals from the surrounding rocks,” Dr Oremland told.

The researchers noticed that the bacteria had colonised small, hot pools, forming colorful “biofilms”.

MonoLake(USGS)

Bacteria living in Mono Lake, California can survive the high levels of arsenic

“We suspected that these bacteria were using arsenic to make a living, so we scraped the biofilms off the rock and studied them under laboratory conditions.”

By first withholding light, then arsenic, the team showed that the bacteria required both to grow.

This the first time an organism has been found that can use arsenic to photosynthesise under anaerobic conditions, Dr Oremland believes.

He suspects that this is an ancient ability in bacteria.

“We think that bacteria were photosynthesising before oxygen was present in the atmosphere,” he said.

Primordial niche

Understanding how arsenic is metabolized by bacteria could help scientists comprehend its damaging affects inside human cells.

Worldwide, 144 million people are exposed to toxic levels of arsenic in their drinking water.

It enters the body’s cells by diffusion; and once inside, it disrupts how they function by binding to their machinery, inactivating it, and disrupting the way energy is transported.

Long-term exposure can lead to skin disease and kidney and bladder cancer, and it is thought to stunt the intellectual development of children.

The most arsenic-contaminated regions are in India, Pakistan, and China, where soluble arsenic in ground waters is above the World Health Organization’s (WHO) suggested maximum safe level of 10 parts per billion.

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