Asteroid served 'custom orders' of life's ingredients

Cosmos Onlineby Iain Coleman

One of the Tagish Lake meteorite fragments.

Credit: Michael Holly, Creative Services, University of Alberta

EDINBURGH: Organic matter found in a meteorite shows how the chemical precursors of life developed in deep space, with some asteroids acting like 'molecular factories' cranking out life's ingredients and shipping them to Earth.

The researchers say that their recent analysis of organic matter found in the Tagish Lake meteorite, which fell to Earth and landed in British Columbia back in 2000, may shed light on how life began on Earth around 4 billion years ago.

"We propose that we are seeing stages of alteration of the organic molecules within this asteroid," said lead author Christopher Herd from the University of Alberta in Canada of the paper published in the current issue of Science.

"If this material was falling on Earth four billion years ago, it could have had an influence on the origin of life."

Organic molecules from deep space

Astronomers have long known that organic molecules can be found in space, in the interstellar molecular clouds from which stars and planets form.

Organic matter, including the amino acids that form the basic building blocks of life, has also been found in a type of meteorite known as carbonaceous chondrites, and it is thought that intense bombardment of the Earth shortly after its formation may have deposited these molecules on our planet.

The new results by Herd and his colleagues show an unprecedented level of diversity in the organic molecules found in a single meteorite, which they interpret as a series of time-steps showing how these vital chemicals were altered by the action of heat and water.

The Tagish Lake meteorite fell upon Canada on 18 January 2000, exploding in a fireball in the upper atmosphere and scattering fragments across the frozen lake. In the process of classifying around four dozen of these fragments, Herd and his colleagues found that was a great deal of variation in their appearance, some dark and sooty, some pale but peppered with dark spots.

Analysing the chemicals contained in some of these fragments, they found that the variations in appearance corresponded with variations in the types of organic molecules present in each fragment.

Snap-shots of chemical evolution

The researchers concluded that the molecules in some of these samples had been altered by chemical processes that were brought about when ice within the asteroid warmed up.

The least altered samples have high levels of amino acids and other molecules important to life, while in the most altered samples these molecules have been flushed out and are no longer present.

This series of snap-shots of chemical evolution within an asteroid will help scientists to understand the processes that affect organic molecules in deep space, and give new insights into the conditions on the surface of the young Earth that gave rise to life.

The results were described as "interesting" by Zita Martins of Imperial College London, who said, "This means that the reactions that happened in the parent body, usually an asteroid, that gave origin to the carbonaceous meteorite are important and influence the organic matter composition of the carbonaceous meteorites."

"The origin of life is not just asteroids and comets," Herd added, "it is also the geology on Earth, but we are getting a better idea of the conditions on early Earth that led to life."