A zircon crystal blasted off the face of Mars before landing on Earth as part of one of the most unusual meteorites ever found has revealed the oldest evidence of water on Mars. Moreover, it has shown that this water sometimes combined with sources of heat, presumably from volcanic activity, similar to those some think started life on Earth. Consequently, there is a new window we previously knew nothing about during which life could have started on our next neighbor out from the Sun.
Most meteorites come from the asteroid belt. A precious few come from Mars, originating when asteroid impacts knocked pieces of the surface into space that eventually landed on Earth. Nineteen of these, all of which landed in the same part of North West Africa, are unlike all the others.
Where every other Martian meteorite provides us with a sample of igneous material from one spot on Mars, the meteorite NWA7034 and its “paired stones” are composed of components from many different places that were fused together into a single rock well before being sent into space. As such, they provide us with insight into the geological history of hundreds of parts of Mars, not just one. “There’s a whole bunch of Martian history here,” Dr Aaron Cavosie of Curtin University told IFLScience
NWA7034 has been nicknamed Black Beauty, and this diversity makes it immensely precious. Buried within Black Beauty is a single crystal thinner than a human hair that has a complex and evolving story to tell that puts all the rest in the shade.
Although NWA7034 is thought to have been knocked off Mars just 5-10 years ago, it fused into rock perhaps 1.5 billion years ago, and the crystals within it are vastly older. Uranium-lead dating allows us to measure when many crystals known as zircons formed, and a large population of those in Black Beauty crystalized between 4.48 and 4.43 billion years ago. Geologists examined a sample of these zircons to see if any of them showed evidence of deformation twins, a consequence of a truly massive shock such as is provided by an object larger than the dino-killer asteroid slamming into a planet.
The first effort in this direction found no zircons with this twinning, leading planetary scientists to the surprising conclusion that impacts this big had stopped by the time most of these crystals formed.
However, Cavosie is part of a team that decided to double-check with a larger sample, just to be sure. Two years ago, they announced that out of more than a hundred they had looked at, one showed the twinning they sought. That flipped the story of early Martian bombardment on its head, showing planet-changing impacts occurred after 4.45 billion years ago, when this zircon formed.
Precious as this zircon is, Cavosie was not done examining it. When he and colleagues searched it for the presence of certain elements, they found metal-rich bands Cavosie compared to layers of an onion when speaking to IFLScience. “Through nano-scale imaging and spectroscopy, the team identified element patterns in this unique zircon, including iron, aluminum, yttrium and sodium. These elements were added as the zircon formed 4.45 billion years ago,” Cavosie said in a statement.
The story of the crucial zircon over its lifetime.
Zircons are sometimes damaged by the radiation captured uranium releases, allowing materials to penetrate after they form. However, Cavosie assured IFLScience that this zircon was “wonderfully crystallized”. That means these layers formed with the crystal. Cavosie’s team went looking for Earthly counterparts with the same layering, in the hope they would indicate how such an exceptional structure could be made. They found them in Australia’s Olympic Dam, the largest deposit of uranium on the planet, with plenty of copper and some gold and silver thrown in for good measure,
Before you start plotting a mining expedition to Mars, Cavosie told IFLScience; “It doesn’t mean this came from an ore deposit.” Instead, this proves the zircon formed under similar circumstances to one from Olympic Dam, which Cavosie called; “A dead ringer”. Olympic Dam was a hydrothermal vent at the time.
This has two major implications. The simple one is that at least some areas of Mars had water 4.45 billion years ago. We know Mars had a wet era, known as the Noachian, probably from 4.1 billion to 3.7 billion years ago. However, very little is known about the period before that, including whether liquid water was present. A single crystal can’t tell us how widespread the water was, but it confirms it existed.
The much bigger (but also less certain) implication is that conditions could have been suited to the presence of life. The argument of whether life began in Darwin’s “warm little pond”, or around a hydrothermal vent goes back and forth regularly, and is unlikely to be settled any time soon. However, if the venters are right, Mars had something very similar.
If life did form along with this precious crystal, it would need to have survived a lot – including at least one epic asteroid impact that would have made Chixulub look like a fender-bender – to still be around today. Cavosie told IFLScience; “Impacts like this vaporize the crust, so life in the immediate vicinity would be destroyed. However, they also drive hydrothermal systems, see Chicxulub. We’re into speculation here, but when I was young I thought large impacts would have sterilized everything, but now I think if there was life beforehand it would have had a chance to survive, unless the whole surface got vaporized.”
It might seem like a coincidence that the same zircon out of more than a hundred that showed evidence of deformation twinning also came with even more valuable information. However, Cavosie told IFLScience that this may just have been because it is the only one his team has examined in this way. They’re planning to correct that, seeing if other zircons in Black Beauty show similar layering.
The study is published open access in the journal Science Advances.
Source Link: Ancient Mars Had Hot Springs Suited To Life, Meteorite Crystal Shows
