ANCIENT flecks of space dust found in a remote corner of Australia is about to blast its way into the science arena. It reveals Earth had something 2.7 billion years ago that it should not have had.

A study from Monash University’s School of Earth, Atmosphere and Environment, published today in the journal Nature, has peered into the composition of some of the oldest fossil micrometeorites — otherwise known as space dust — ever found.

The team, led by Dr Andrew Tomkins, found the micrometeorites were once space dust composed largely of metallic iron. This iron had been oxidised as the dust plunged through Earth’s primeval atmosphere.

This was a big surprise: Geologists have clearly shown that there simply should not have been enough oxygen around 2.7 billion years ago to do such a thing.

Earth’s first oxygen-producing algae only appeared slightly before 2.4 billion years, sparking a ‘great oxidation’ event that charged our atmosphere with the life-giving gas.

The discovery also has significant implications in the search for life among other worlds: Finding oxygen in a distant atmosphere may not be the deadset giveaway it was believed to be.

FIRE IN THE SKY

In a study published in the journal Nature today, Dr Tomkins has used these flecks of space dust to challenge the accepted view that Earth’s early atmosphere was entirely oxygen-poor.

Instead, the outer envelope may have had just as much oxygen as we see today.

Cosmic dust expert Dr Matthew Genge of the Imperial College was asked to calculate what level of atmospheric oxygen would be needed to explain the level of oxidisation the micrometeorites revealed.

“This was a surprise because it has been firmly established that the Earth’s lower atmosphere was very poor in oxygen 2.7 billion years ago; how the upper atmosphere could contain so much oxygen before the appearance of photosynthetic organisms was a real puzzle,” Dr Genge said.

EXPLORE MORE: An Australian astrophysicist may have just killed ET

Dr Tomkins believes he knows where the oxygen may have come from. And it may explain why it was so high in the sky.

Carbon dioxide could have been blasted apart by ultraviolet light from the Sun, releasing oxygen atoms from their bond with the carbon.

So it’s possible that the established and new views may both be right: The oxygen was all likely trapped in the upper atmosphere — kept there by a thick, heavy methane haze which blanketed the Earth’s surface.

“It is incredible to think that by studying fossilised particles of space dust the width of a human hair, we can gain new insights into the chemical makeup of Earth’s upper atmosphere, billions of years ago.” Dr Tomkins said.

SECRETS IN THE STONE

The ancient space dust was found embedded in limestone collected in Western Australia’s remote Pilbara region.

They were then examined in fine detail at the Monash Centre for Electron Microscopy (MCEM) and the Australian Synchrotron.

“Because this dust was so small, all this oxidisation must have occurred at 90 to 75km in altitude, while the particles were superheated shooting stars,” Dr Tomkins said.

“This was an exciting result because it is the first time anyone has found a way to sample the chemistry of the ancient Earth’s upper atmosphere.”

At this point, 2.7 billion years ago, the Earth’s atmosphere was CO2 rich with possibly a methane haze. The planet’s surface was little more than rock and water, but single-celled life called methanogens were busily burping methane after digesting hydrogen from nearby volcanoes.

Methane is a strong greenhouse gas, so it would have heated up the lower atmosphere — reducing the likelihood of mixing with the upper atmosphere.

Meanwhile, the sky would also have been filled with meteors as the final clouds of dust left over from the solar system’s formation were swept up.

Dr Tomkins says he is keen to take his research further by sampling space dust fossilised in rocks formed during different points of the Earth’s evolution.

“We will focus particularly on the great oxidation event, which happened 2.4 billion years ago when there was a sudden jump in oxygen concentration in the lower atmosphere,” he said.

ALIEN IMPLICATIONS

With the list of freshly discovered — potentially habitable — exoplanets growing exponentially, Dr Tomkins’ findings may have implication for the next step: observing their atmospheres.

“They’re actually close to being able to do that,” Dr Tomkins says.

CO2 rich atmospheres are believed to be quite common, with compositions similar to Venus.

But the micrometeorite study shows even dead atmospheres such as these could have quantities of oxygen — which is why detecting it may not be the signpost of habitability it is thought to be.

Instead, astronomers would need a combination of methane and oxygen before the ‘habitable’ label could be applied, he says.

Micrometorites could also tell us much more about the geological history of Mars.

“There should be lots of micrometeorites on the surface of Mars,” Dr Tomkins says. “Rovers could potentially look for these and — if they could date the age at which they fell — they can look at Mars’ atmosphere as it was in the past.”

@JamieSeidel