In September 1969, a meteorite crashed into Murchison, in regional Victoria. The 'Murchison Meteorite' contained an extraordinary surprise; the first organic molecules of extra-terrestrial origin.
Located 167 km north of Melbourne, Murchison is a sleepy Victorian country town, nestled alongside the Goulburn River.
Primarily an agricultural centre, the town was founded by settlers from Tasmania in 1840. It expanded during the gold rush in Victoria in the 1850s, where it was a key stopover and supply point for local prospectors.
Otherwise, the town is wholly unremarkable, a highly unlikely spot for a revolutionary scientific discovery.
On September 28, 1969, residents across Victoria were startled when a blazing fireball erupted above them.
Clearly visible in the Sunday afternoon sun, the meteorite streaked across the rural skies. Witnesses reported loud explosions, crackling, smoke and a strange smell, like methylated spirits;
'I saw smoke in the sky, and soon after there was an explosion.
It seemed like an earth tremor. Our next door neighbour was knocked over by it.
It rattled the buildings, and gave us a hell of a shock.'
- Mervyn Hellford, eyewitness
Weighing 100 kilos, the meteorite finally disintegrated above Murchison, showering the surrounding area with approximately 2 000 chunks of space debris.
Curious locals immediately began recovering the fragments, and either keeping them as souvenirs, or turning them in to the local authorities.
Within a few days, samples were sent to Melbourne University for further analysis. John Lovering, then a professor of Geology at the university, received the first samples in a plastic bag:
'I opened it (the bag) up, and suddenly this great organic chemistry smell hit me. It was very very strong.
It looked like a lump of coal. And I knew what it was straight off; a carbonaceous chrondite. One of the most primitive of all of the meteorites.
It was very exciting.'
- John Lovering
The preliminary results showed that the Murchison Meteorite 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 chondrite was proved correct, and so made the find particularly rare.
After the preliminary analysis was completed in Melbourne, rock samples were sent to NASA for a more detailed assessment.
The scientific community was rocked in 1970 when the team at NASA 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, terrestrial chemistry.
These were the first organic molecules ever discovered on an extra-terrestrial 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 their head.
While many aspects of the origins, and development, of life on earth are well known, some parts remain a mystery.
The Darwinian theory of evolution and natural selection has wide acceptance, but there is still debate in the scientific community about what may have started this process off. Did lightning in the earth's primitive atmosphere trigger the first organic chemistry? Did the first molecules develop at super heated vents on the ocean floor? Is there simply some unknown process at play, awaiting discovery?
The earth was formed approximately 4.5 billion years ago, and the earliest signs of life that have been detected - microscopic bacterial fossils - have been dated to 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 discovery of amino acids in the Murchison Meteorite provided the pathway to a new theory; perhaps the first organic molecules arrived on a meteorite. This interpretation of the Murchison Meteorite was hugely controversial when it was announced, and debate around the amino acid discovery remains fierce to this day.
Another element was added to the debate in 1996.
In 1984, NASA recovered meteorite fragments from Antarctica. Subsequent analysis, and comparison to Martian rock samples, allowed them to determine that the meteorite had originated on Mars.
Dubbed the 'Allan Hills Meteorite', after the mountainous region where it was found, it was determined that the rock was approximately 4 billion years old, and had crashed into earth about 13 000 years ago.
In 1996, NASA announced that the meteorite may contain fossils of microscopic bacteria.
In a paper published in the journal 'Science', research lead David McKay presented several pieces of evidence to suggest the Allan Hill meteorite showed evidence of life.
Chief among these was the presence of microscopic magnetite crystals, a by-product of organic chemistry well known from earth based biology. At the time, these crystals were only known to be formed by bacteria, and so presented a compelling argument that bacterial life had once existed on Mars.
If this were correct, it was easy to extrapolate that a similar meteorite may have arrived on earth billions of years ago, and brought the first traces of life to this planet with it. Were we all, in fact, Martians?
But in subsequent years, many of the conclusions from the 1996 research have been called into question. It was later shown that magnetite crystals can also be formed by the shock wave from intense explosions, of which the early solar system would have been rife.
Nevertheless, the question of whether the Allan Hills meteorite contains Martian fossils remains open, debated by passionate supporters and sceptics.
The findings from the Murchison meteorite also remain significant, and are subject to ongoing discussion. In the decades since the amino acids were first discovered, they have been detected numerous times on off-earth objects, including meteorites, asteroids, and even the surface and tail of Halley's Comet.