The meteorite Northwest Africa (NWA) 7034, known more commonly as Black Beauty, was discovered in the Moroccan Sahara desert back in 2011.

“We knew right away it was special. It was different from anything we had ever seen,” says Dr. Francis McCubbin, from the Institute of Meteoritics at the University of New Mexico, whose team helped identify the meteorite as Martian in origin.

Black Beauty’s unique appearance, with large clasts sitting in a fine grained matrix, is thought to result from its formation from impact or pyroclastic volcanism debris that later cemented back together, forming what’s known as a breccia.

These fragments were shown by Kevin Cannon at Brown University in 2015 to include 4.4 billion-year-old chunks of Martian crust — the only examples of the Red Planet’s original bedrock ever to make it to Earth.

In a new paper published in the Journal of Geophysical Research Planets, McCubbin’s team presents the results of a new rigorous analysis of the meteorite and its clasts.

Geochemistry and geochronology assessments were carried out with the hope of finding out more about early sedimentary processes on Mars and even whether the planet was once a warm, wet place, habitable for life.

“This is the most comprehensive study so far of a meteorite that probably tells us more about Mars’ history than every other Martian meteorite put together,” says Cannon, who wasn’t involved in this latest study.

However, McCubbin’s team’s hopes of drawing conclusions about ancient Martian surface processes were dented by the heating that accompanied the formation of the breccia around 1.5 billion years ago.

“This event erased a lot of evidence of previous history, limiting what we could learn,” McCubbin says.

“It’s actually an important lesson for future Mars missions — to avoid recovering samples with these complex thermal histories.”

Whilst clues to early sedimentary process were limited, their analysis did reveal new details of the planet’s volcanic history.

This history was recorded in the form of volcanic clasts which had previously been identified as alkali basalt lavas.

In their new paper, McCubbin’s team described these clasts as the earliest evidence of so-called oxidized volcanism on the Red Planet, where lavas form from oxidized upper crustal rock.

The beginnings of oxidized volcanism on Mars and its implications for the planet’s early surface conditions have been a matter of debate in recent years.

In 2013, Dr. Bernard Wood and colleagues at Oxford University looked at the Mars Spirit Rover’s analysis of surface volcanic rocks dating back 3.7 billion years and showed they came from a more oxygen-rich environment than the younger volcanic rocks present in more common classes of Martian meteorite.

They suggested this was probably caused by recycling of oxygen-rich materials from the surface into the interior and inferred the Martian surface and atmosphere were also ‘oxidized’ at this point in Mars history, 1.5 billion years before Earth’s own atmosphere became ‘oxygen rich.’

However, at the time, McCubbin disputed the atmospheric interpretation of the data, stating Wood’s team’s analysis only showed the upper mantle was more oxidized than the deep interior, a state of affairs which doesn’t necessarily require any surface oxygen gas.

Whatever Wood’s findings implications for the early Martian atmosphere, McCubbin’s latest paper pushes back the date for early oxidized volcanism on Mars by more than half a billion years.

The key piece of evidence came from a zircon grain found within one of the oxidized basalt clasts.

Zircon is a valuable tool for geologists as it readily incorporates radioactive uranium atoms which decay at constant rate, allowing it, and the oxidized basalt clasts around it to be dated to 4.4 billion years old.

“We have dated the oldest example of oxidized alkali basalt, which pushes the onset of oxidized volcanism on Mars to very early,” says McCubbin.

“Whilst question remain as to what oxidation levels of volcanism can say about atmospheric conditions, there are also questions to be answered about the origin of oxidized alkali volcanism in the first place,” says Cannon.

“The alkali-rich volcanism described in the paper is similar to that which continues to form the Hawaiian island chain, however we believe Mars never had true plate tectonics like on Earth. So exactly why this type of volcanism took place is a mystery.”

And even if surface oxygen is still in doubt, the presence of a gradient of oxidation within the layers of the Martian crust and mantle could still provide hope for ancient life.

Back in 2015, McCubbin told the BBC: “substantial redox gradients with depth on Mars… could be potentially very important for Mars’ habitability because some organisms can take advantage of redox reactions and use them as an energy/food source.”

Regardless of its surface’s suitability for life, we can at least say that within its ancient crust potentially habitable conditions existed even earlier in Mars’ history, giving any possible life half a billion more years to emerge and possibly evolve.

Source: Sci-News