Mars meteorite NWA 7034, AKA 'Black Beauty'. (Institute of Meteoritics, UNM)
SPACE
MICHELLE STARR
2 FEBRUARY 2022
Evidence for an intense asteroid impact on Mars has been found in a Martian meteorite, which could alter the timeline for when the red planet might have been habitable.
In a famous meteorite named NWA 7034, or 'Black Beauty', scientists discovered a shocked crystal of the mineral zircon, showing a feature only seen on Earth in massive impact craters. This suggests that Mars was under heavy bombardment from meteorites later than thought.
"This grain is truly a one-off gift from the Red Planet," says planetary geologist Morgan Cox of Curtin University in Australia.
"High-pressure shock deformation has not previously been found in any minerals from Black Beauty. This discovery of shock damage in a 4.45 billion-year-old Martian zircon provides new evidence of dynamic processes that affected the surface of early Mars."
NWA 7034, discovered in 2011 in the Sahara Desert of Morocco, is a 320-gram (11.3-ounce) chunk of volcanic breccia. That is, it's composed of pieces of different types of rock, a bit like a fruit cake.
It's mostly basalt, but it's scattered through with inclusions, including a number of crystals of zircon, and parts of it are up to 4.45 billion years old, nearly as old as the planet itself.
The early Solar System was a much wilder place than it is today. We've found evidence that, early on, the inner planets were absolutely pummeled by large asteroid impacts.
The overall absence of shock damage in the zircons from NWA 7034 was previously given as evidence that this intense period of bombardment on Mars had declined by about 4.48 billion years ago. Consequently, this could have meant that Mars was habitable quite early on.
Cox and her colleagues followed up by performing a close study of 66 grains of zircon found in NWA 7034, performing electron backscatter diffraction mapping and cathodoluminescence imaging to probe the structural arrangement of the atomic lattice within.
In just one of the 66 grains, one that was 4.45 billion years old, the team identified evidence of a massive impact.
"The type of shock damage in the Martian zircon involves 'twinning', and has been reported from all of the biggest impact sites on Earth, including the one in Mexico that killed off the dinosaurs, as well as the Moon, but not previously from Mars," Cox said.
In all minerals, atoms are arranged in a symmetrical three-dimensional lattice structure. Think of, for example, a lattice cube, where an atom sits at each corner of every cube in the lattice (although the actual structure varies significantly from mineral to mineral).
When high enough pressure is applied – 20 to 30 gigapascals, such as we see in the biggest asteroid impacts – something strange can happen to these lattices. Crystals can be pushed together so tightly that they end up sharing some of the points on their crystal lattices.
Although the team only found twinning in one of their zircon crystals, that one crystal suggests a formation process similar to what we have seen here on Earth, involving high pressure, likely from an asteroid impact. This, the researchers said, suggests that heavy bombardment on Mars was occurring at least 30 million years after the previous estimate.
In turn, this suggests that conditions may not have been amenable for life until a bit later, too – which coincides with the Mars timeline for another condition for life as we know it, the researchers say.
"Prior studies of zircon in Martian meteorites proposed that conditions suitable for life may have existed by 4.2 billion years ago based on the absence of definitive shock damage," says planetary geologist and geochemist Aaron Cavosie of Curtin University.
"Mars remained subject to impact bombardment after this time, on the scale known to cause mass extinctions on Earth. The zircon we describe provides evidence of such impacts, and highlights the possibility that the habitability window may have occurred later than previously thought, perhaps coinciding with evidence for liquid water on Mars by 3.9 to 3.7 billion years ago."
Given that prolonged heavy asteroid bombardment would have had the potential to vaporize any surface water and disrupt the atmosphere, though, perhaps that's not such a coincidence after all.
The research has been published in Science Advances.
WAIT, WHAT?
Did humans live on Mars?First ever zircon crystal found in Africa gives new hope
Updated At: Feb 04, 2022
Mars is currently the most popular exploration target to search for evidence of life elsewhere.
Updated At: Feb 04, 2022
Mars is currently the most popular exploration target to search for evidence of life elsewhere.
YPhoto for representational purpose only. iStock
PTI
Perth, February 3
Are we alone in the Universe? Billions of dollars are being spent trying to answer that simple question. The implications of finding evidence for life beyond Earth are staggering. The “before and after” mark would punctuate human history.
Mars is currently the most popular exploration target to search for evidence of life elsewhere. Yet little is known about its early history. Our research on a Martian meteorite provides new clues about early surface conditions on the red planet.
Windows into the past
Today Mars is cold and inhospitable. But it may have been more Earth-like and habitable in a bygone era. Landforms on Mars record the action of liquid surface water, perhaps as early as 3.9 billion years ago.
Like Earth, early Mars was subject to a global bombardment from chunks of rock and ice floating around the Solar System. Giant impacts both destroy and create favourable environments for life. So to untangle when conditions suitable for life may have arisen on Mars, we have to track the history of both water and impacts.
A flotilla of rovers and orbiting spacecraft have been dispatched to Mars, with two NASA rovers specifically exploring impact craters for evidence of past life. Samples collected by rovers will be returned in future missions.
For now, meteorites are the only samples of Mars available to study here on Earth. Martian meteorites are born when an impact on Mars ejects rocky fragments that later intercept Earth's orbit. Most Martian meteorites are igneous rocks, such as basalt. One meteorite, NWA 7034, is different, as it represents a rare sample of the surface of Mars.
Sending shock waves
The NWA 7034 meteorite, weighing about 320g, was found in the desert of northwest Africa and first reported in 2013. Unique oxygen isotope signatures reveal its origin from Mars. Other meteorites blasted off of Mars during the same event have since been found.
NWA 7034 is a complicated rock made of broken rock and mineral shards called “breccia”. Its various fragments record different snippets of Martian history.
Tiny grains of the mineral zircon occur in NWA 7034. Zircon is a “geochronometer”, meaning it records (and reveals to us) how much time has passed since it crystallised from magma. Prior studies of NWA 7034 found it contains the oldest known zircons from Mars – some up to 4.48 billion years old.
Zircon is quite useful for studying meteorite impacts. It preserves microscopic damage caused by the passage of shock waves, and these “shocked grains” provide a solid record of impact. However, no zircons with definitive shock damage had been identified in previous studies of NWA 7034.
NWA 7034 is similar to a type of sedimentary rock on Earth called conglomerate. In such rocks, every mineral can have a different origin. With that in mind, we set out to survey additional zircon grains in NWA 7034 to see if we could find any that recorded evidence of impact.
We looked at more than 60 zircons, but found only one shocked grain. This means the impact occurred before the grain was mixed into the pile of fragments that became a rock.
Reassessing Mars's timelines
The type of shock features we found are called “deformation twins”. High pressure shock waves squeeze zircon like an accordion. This process can reorganise atoms within the crystal, to form a duplicated “twin” of zircon, which we can detect.
We determined the zircon crystallised 4.45 billion years ago, making it one of the oldest zircons known from Mars – even older than the oldest known piece of Earth (also a zircon).
We don't know what kind of rock the shocked zircon originally formed in. The original igneous host rock was ripped apart during impacts on Mars. The zircon is a broken fragment from a larger grain mixed in with the matrix of the meteorite.
We do, however, know where shocked zircons like this are made. On Earth, shocked zircons with deformation twins are only found at impact craters. Moreover, they occur at all of Earth's largest asteroid strikes.
Zircons with shock features have been found at Vredefort in South Africa, Sudbury in Canada and Chicxulub in Mexico. The Mexican crater formed about 65 million years ago, and has been linked to the extinction of the dinosaurs. In this case, shocked zircons were one product of an impact large enough to cause a mass extinction.
Prior studies cited an absence of shock features in zircon from NWA 7034 to indicate a decline in catastrophic impacts on Mars by 4.48 billion years. It was further proposed that habitable conditions existed as of 4.2 billion years ago.
However, the shocked zircon we found crystallised 4.45 billion years ago. The shock event would have had to have occurred at least 30 million years after Mars had supposedly stopped being bombarded.
When exactly was the impact?
Although determining the precise age of impact is difficult, geochemical studies of NWA 7034 reveal its main components were subject to meteorite impacts before roughly 4.3 billion years ago. In this scenario, the zircon may have been shocked during this time, somewhere between 4.3 and 4.45 billion years ago.
Alternatively, it may have formed more recently, but before a decline in the rate of impacts earlier than 3 billion years ago. Both land forms and water-bearing minerals argue for early surface water on Mars, possibly by 3.9 to 3.7 billion years ago. This may be the best indicator for when habitable conditions existed.
Our findings raise new questions about the early impact history of Mars. Determining the origin of the shocked zircon, and time of impact, will provide better context for interpreting the planet's history as archived in meteorite NWA 7034 – and potentially a timeframe for when conditions for life may have emerged.
PTI
Perth, February 3
Are we alone in the Universe? Billions of dollars are being spent trying to answer that simple question. The implications of finding evidence for life beyond Earth are staggering. The “before and after” mark would punctuate human history.
Mars is currently the most popular exploration target to search for evidence of life elsewhere. Yet little is known about its early history. Our research on a Martian meteorite provides new clues about early surface conditions on the red planet.
Windows into the past
Today Mars is cold and inhospitable. But it may have been more Earth-like and habitable in a bygone era. Landforms on Mars record the action of liquid surface water, perhaps as early as 3.9 billion years ago.
Like Earth, early Mars was subject to a global bombardment from chunks of rock and ice floating around the Solar System. Giant impacts both destroy and create favourable environments for life. So to untangle when conditions suitable for life may have arisen on Mars, we have to track the history of both water and impacts.
A flotilla of rovers and orbiting spacecraft have been dispatched to Mars, with two NASA rovers specifically exploring impact craters for evidence of past life. Samples collected by rovers will be returned in future missions.
For now, meteorites are the only samples of Mars available to study here on Earth. Martian meteorites are born when an impact on Mars ejects rocky fragments that later intercept Earth's orbit. Most Martian meteorites are igneous rocks, such as basalt. One meteorite, NWA 7034, is different, as it represents a rare sample of the surface of Mars.
Sending shock waves
The NWA 7034 meteorite, weighing about 320g, was found in the desert of northwest Africa and first reported in 2013. Unique oxygen isotope signatures reveal its origin from Mars. Other meteorites blasted off of Mars during the same event have since been found.
NWA 7034 is a complicated rock made of broken rock and mineral shards called “breccia”. Its various fragments record different snippets of Martian history.
Tiny grains of the mineral zircon occur in NWA 7034. Zircon is a “geochronometer”, meaning it records (and reveals to us) how much time has passed since it crystallised from magma. Prior studies of NWA 7034 found it contains the oldest known zircons from Mars – some up to 4.48 billion years old.
Zircon is quite useful for studying meteorite impacts. It preserves microscopic damage caused by the passage of shock waves, and these “shocked grains” provide a solid record of impact. However, no zircons with definitive shock damage had been identified in previous studies of NWA 7034.
NWA 7034 is similar to a type of sedimentary rock on Earth called conglomerate. In such rocks, every mineral can have a different origin. With that in mind, we set out to survey additional zircon grains in NWA 7034 to see if we could find any that recorded evidence of impact.
We looked at more than 60 zircons, but found only one shocked grain. This means the impact occurred before the grain was mixed into the pile of fragments that became a rock.
Reassessing Mars's timelines
The type of shock features we found are called “deformation twins”. High pressure shock waves squeeze zircon like an accordion. This process can reorganise atoms within the crystal, to form a duplicated “twin” of zircon, which we can detect.
We determined the zircon crystallised 4.45 billion years ago, making it one of the oldest zircons known from Mars – even older than the oldest known piece of Earth (also a zircon).
We don't know what kind of rock the shocked zircon originally formed in. The original igneous host rock was ripped apart during impacts on Mars. The zircon is a broken fragment from a larger grain mixed in with the matrix of the meteorite.
We do, however, know where shocked zircons like this are made. On Earth, shocked zircons with deformation twins are only found at impact craters. Moreover, they occur at all of Earth's largest asteroid strikes.
Zircons with shock features have been found at Vredefort in South Africa, Sudbury in Canada and Chicxulub in Mexico. The Mexican crater formed about 65 million years ago, and has been linked to the extinction of the dinosaurs. In this case, shocked zircons were one product of an impact large enough to cause a mass extinction.
Prior studies cited an absence of shock features in zircon from NWA 7034 to indicate a decline in catastrophic impacts on Mars by 4.48 billion years. It was further proposed that habitable conditions existed as of 4.2 billion years ago.
However, the shocked zircon we found crystallised 4.45 billion years ago. The shock event would have had to have occurred at least 30 million years after Mars had supposedly stopped being bombarded.
When exactly was the impact?
Although determining the precise age of impact is difficult, geochemical studies of NWA 7034 reveal its main components were subject to meteorite impacts before roughly 4.3 billion years ago. In this scenario, the zircon may have been shocked during this time, somewhere between 4.3 and 4.45 billion years ago.
Alternatively, it may have formed more recently, but before a decline in the rate of impacts earlier than 3 billion years ago. Both land forms and water-bearing minerals argue for early surface water on Mars, possibly by 3.9 to 3.7 billion years ago. This may be the best indicator for when habitable conditions existed.
Our findings raise new questions about the early impact history of Mars. Determining the origin of the shocked zircon, and time of impact, will provide better context for interpreting the planet's history as archived in meteorite NWA 7034 – and potentially a timeframe for when conditions for life may have emerged.
PTI
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