Sunday, April 10, 2016

Fire from the Sky

September 28, 1969: Two months after NASA landed a manned spaceship on the moon, an extraterrestrial visitor returned the favour; a chunk of ancient rock streaked high above Victoria. Coming to ground near Murchison, in the states north, the meteorite was to prove more than just an exciting light show.

Once parts of the meteorite were recovered, scientists were amazed to discover that the rock contained amino acids, organic molecules that are the building blocks of our DNA. Previously, amino acids had only ever been known on earth, and it had been thought that the conditions outside of our atmosphere would be too harsh for them to form, or survive.

The discovery raised a tantalising possibility: could life have actually evolved somewhere other than Earth, then hitched a ride here on a meteorite?

Headline in The Argus

On September 28, 1969, residents across Victoria were startled when their Sunday afternoon was rocked by a blazing fireball that erupted above them. Witnesses across the state reported loud explosions, crackling sounds, smoke and a strange smell, like methylated spirits, as a meteorite left a flaming trail across the sky:

Weighing approximately 100kg, the meteorite finally disintegrated above Murchison, a small town in the Goulburn Valley, about 160km north of Melbourne. Breaking up into about 2 000 chunks, some weighing as much as 5kg, the fiery debris rained down over the town and the surrounding farmland.
Curious locals immediately began recovering meteorite fragments, and either keeping them as souvenirs, or turning them in to the local authorities.

Samples were sent to Melbourne University for analysis, and for comparison to some samples of moon rock, which had also recently arrived:

The preliminary results showed that the rock was at least 4.5 billion years old, and so was likely older than the earth itself. Professor Lovering's guess that it was a carbonaceous chrondite was proved correct, and so made the find particularly rare.

And there the matter may have rested.

A Murchison Meteorite fragment at the Melbourne Museum.
But the scientific community was rocked in 1970 when a team at NASA, studying rocks from the meteorite, announced the presence of 74 different amino acids in their samples. The majority were exotic molecules not found on earth but, remarkably, 6 were common amino acids known from organic chemistry.

These were the first organic molecules ever discovered on an extraterrestrial body.

And that these molecules were found in a rock older than the Earth, and that they had somehow survived in the vacuum of space for many millions of years, turned theories of life's evolution on our planet on their head.

The origin of life on earth was (and still is) a mystery. While some aspects of life on our planet are well understood, there is still no consensus on how it came to originate in the first place. Chief among these mysteries; the earth was formed approximately 4.5 billion years ago, and the earliest signs of life that have been detected - microscopic fossils from bacteria - about 4.2 billions year ago, when the planet would still have been cooling and largely inhospitable.

How then did life take hold so quickly?

The Murchison Meteorite provided the pathway to a new theory; that organic molecules arrived on earth from space, and then adapted to conditions here. As distinguished a scientist as Francis Crick, co-discoverer of DNA, was an enthusiastic proponent of this theory, in light of the Murchison Meteorite findings.

A microscopic fossil from mars, or just a squiggley thing?
The debate continues to this day.

The organic chemistry found on the Murchison meteorite has been detected in many other celestial bodies; subsequent meteorites and asteroids and even on Halley's Comet. Our solar system, it seems, is awash in complex organic molecules.

Which doesn't provide an answer to the question, where did Earth's organic chemistry originate? Both sides of the argument have their supporters among the scientific community, although the majority opinion still favours that the compounds that exist in our DNA were formed independently on earth.

The argument was enlivened in 1996 when NASA announced that meteorite fragments it recovered from Antarctica in 1984 had originated on Mars, and contained evidence of fossilised bacteria (pictured above). They subsequently backed away from this claim, but whether these rocks contain fossils, or just exotic mineral deposits, is still a matter of dispute.

Analysis of both the Martian and Murchison meteorites continues.

Murchison today.
But whether this problem is ever satisfactorily solved, it is remarkable to think that the entire debate was kicked off in sleepy Murchison, population 600.

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