Jennifer Carpenter

A new technique has been helping scientists piece together how the Earth’s continents were arranged 2.5 billion years ago.

The novel method allows scientists to recover rare minerals from rocks.

By analysing the composition of these minerals, researchers can precisely date ancient volcanic rocks for the first time.

By aligning rocks that have a similar age and orientation, the early landmasses can be pieced together.

This will aid the discovery of rocks rich in ore and oil deposits, say the scientists. The approach has already shown that Canada once bordered Zimbabwe, helping the mining industry identify new areas for exploration.

Dr Wouter Bleeker, from the Geological Survey of Canada, explained that much of the geology that exists today formed around 300 million years ago when the supercontinent Pangea existed.

“We really don’t understand the [Earth’s] history prior to Pangea,” he told a recent meeting of the American Geophysical Union in Toronto.

Early landmasses

Analysis of rocks that formed when continents drifted apart can help geologists reconstruct early landmasses.

Dr Richard Ernst, a geologist from the University of Ottawa, explained that molten magma fills the cracks formed by shifting continental plates.

The magma cools to form long veins of basalt – a volcanic rock – that has a “distinct magnetic signature” revealing the rock’s orientation and latitude when it formed.

By combining this “magnetic signature” with the ages of these rocks, researchers can tell whether rocks on different continents were once part of the same volcanic up-welling.

But until now, researchers have been unable to determine the ages of many of these ancient rocks because of the difficulty in extracting the minerals used to date them.

“We are dealing with such small mineral crystals – typically much less than 100 microns long – we are talking about grains far smaller than the width of a human hair,” explained Dr Michael Hamilton, a geologist and co-leader on the project.

But with the development of new techniques, minerals – such as baddeleyite – can now be successfully recovered.

Baddeleyite is useful because it incorporates large amounts of uranium into its crystal-structure, and because uranium naturally decays to lead. Scientists also know the rate at which this happens.

“[They] can use these minerals as radioactive clocks,” Dr Hamilton added.

“All we need to do is measure the the amounts of uranium and lead very precisely.”

In a large, international project, researchers hope to collect and date 250 rocks from around the world, and use this information to reconstruct how these continental fragments were once together to form giant landmasses that existed 2.5 billion years ago.

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Formic acid, a molecule implicated in the origins of life, has been found at record levels on a meteorite that fell into a Canadian lake in 2000.

Cold temperatures on Tagish Lake prevented the volatile chemical from dissipating quickly.

An analysis showed four times more formic acid in the fragments than has been recorded on previous meteorites.

The researchers told a meeting of the American Geophysical Union that the formic acid was extraterrestrial.

Formic acid is one of a group of compounds dubbed “organics”, because they are rich in carbon.

“We are lucky that the meteorite was untouched by humans hands, avoiding contamination by organic compounds that we have on our fingers,” said Dr Christopher Herd, the curator of the University of Alberta’s meteorite collection.

Samples of the meteorite totalling 850 grams were collected from Tagish Lake in Canada, purchased in 2006 by a consortium including the Royal Ontario Museum and recently subjected to chemical analysis.

The scientists found levels of formic acid four times higher than had previously been recorded on a meteorite. Studies have until recently focused on the Murchison meteorite that landed in a town of that name in Australia in 1969.

“The interesting thing is that we do see this variability between meteorites, seeming to have increased enrichments of one particular compound over another,” said Mark Sephton, a meteorite and geochemistry professor at Imperial College London.

“This has for a while been overlooked as we concentrated predominantly on the Murchison meteorite, but now we’ve got another fresh sample and we can start to analyse a different portion of the asteroid belt and therefore a different portion of the Solar System.”

Primordial kitchen

The particular types, or isotopes, of hydrogen that are found in the formic acid show that it most likely formed in the cold regions of space before our Solar System existed.

On Earth, formic acid is commonly found in the stings of insects such as ants, but Professor Sephton said it is likely to have been an important “ingredient in the kitchen” on Earth before life began.

The acid is known to act as a “reducing agent” – acting as a magnet for oxygen atoms during chemical reactions – and facilitate the conversion of some amino acids into others.

It may also be implicated in the transformation of the more primitive RNA into DNA.

Only one of the four “nucleobases” that make up RNA and DNA is different between the two: uracil is present in RNA while thymine takes its place in DNA.

Professor Sephton’s team found uracil in the Murchison meteorite, but no measurable amount of thymine. However, formic acid is known to help along the reaction that converts the uracil into thymine.

The reaction, he said, is “one of the ways in which you can take some simple molecules and increase the chemical diversity of the pool of pre-biotic molecules”.

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