Black Beauty, a rock discovered in the Sahara Desert, has been identified as the oldest Martian meteorite ever found, scientists say.
Earlier research had suggested Black Beauty was about 2 billion-year old, but new tests indicate the rock actually dates to 4.4 billion years ago.
The dark and glossy meteorite would have formed when the Red Planet was in its infancy.
The research is published in the journal Nature.
Lead author Prof. Munir Humayan, from Florida State University, US, said: “This [rock] tells us about one of the most important epochs in the history of Mars.”
There are about 100 Martian meteorites, but almost all of them are younger, dating to between 150 million and 600 million years old.
They would have fallen to the Earth after asteroid or comet impacts had dislodged them, setting the rocks free to travel through space before eventually crash landing here.
This particular Martian meteorite, which is formed of five fragments, is much older.
Black Beauty rock has been identified as the oldest Martian meteorite ever found
An earlier analysis of one piece, called NWA 7034, put the age at 2 billion years.
But this latest research has found that another piece, NWA 7533, dates to 4.4 billion years ago, which suggests that NWA 7034 also must be older.
The team said it would have formed when Mars was just 100 million years old.
“It is almost certainly coming from the southern highlands – the cratered terrain that makes up the southern hemisphere of Mars,” said Prof. Munir Humayan.
This would have been a turbulent period of Martian history, when volcanoes were erupting all over the surface.
Prof. Munir Humayan explained: “The crust of Mars must have differentiated really quickly, rather than gradually over time. There was a big volcanic episode all over the surface, which then crusted up, and after that the volcanism dropped dramatically.
“When it did this it also must have out-gassed water, carbon dioxide, nitrogen and other gases to produce a primordial atmosphere… and also a primordial ocean.”
He added: “This is a very exciting period of time – if there were to be life on Mars, it would have originated at this particular time.”
Prof. Munir Humayan said that team now plans to study the rock to see if there were any signs of past life. But he added that while the rock was lying in the Sahara Desert, living organisms probably would have occupied it, masking potential evidence.
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Scientists have discovered that a dark lump of rock found in the Moroccan desert in 2011 is a new type of Martian meteorite.
Weighing 320 g, the stone has been given the formal name Northwest Africa (NWA) 7034 – but is nicknamed “Black Beauty”.
Its texture and chemistry set it apart from all previous objects picked up off the surface of Earth but known to originate on the Red Planet.
The researchers’ analysis, reported in Science magazine, shows the meteorite to be just over two billion years old.
The study was led by Carl Agee from the University of New Mexico, US.
“It has some resemblance to the other Martian meteorites but it’s also distinctly different in other respects, both in the way it just looks in hand sample, but also in its elemental composition,” Carl Agee said.
There are just over 100 Martian meteorites currently in collections worldwide. They were all blasted off the Red Planet by some asteroid or cometary impact, and then spent millions of years travelling through space before falling to Earth.
Scientists say that a dark lump of rock, nicknamed Black Beauty, found in the Moroccan desert in 2011, is a new type of Martian meteorite
Their discovery was mostly chance (few were seen in the act of falling) but their dark forms mean they will have caught the eye of meteorite hunters who scour desert sands and polar ice fields for rare rocks that can trade for tens of thousands of dollars.
Virtually all the Martian meteorites can be put in one of three classifications referred to as Shergotty, Nakhla, and Chassigny after key specimens. Scientists will often refer to these rocks simply as the SNC meteorites.
Prof. Carl Agee and colleagues argue that NWA 7034 now be put in its own class.
This rock is a basaltic breccia in character. It is made of a jumble of fragments that have been cemented back together in the high temperatures of a volcanic eruption. There are many examples of Moon meteorites that look this way, but no SNC ones.
Geochemically, NWA 7034 is dominated by alkali elements such as potassium and sodium. This is precisely what the robot rovers studying basalts down on the ground on Mars also see. This is not a trait seen in the SNC meteorites, interestingly.
Prof. Carl Agee’s team also see much more water in the new meteorite – about 6,000 parts per million. That is about 10 times more water bound into the rock than is the case in the most water-rich SNC specimens.
This says something about the environment in which the rock formed, indicating there was a much greater abundance of water to interact with the basalt.
“This rock is from two billion years ago and a lot of the SNCs are from only about 200-400 million years ago,” explained Prof. Carl Agee.
“And of course those most recent times on Mars have witnessed a cold, dry planet with a thin atmosphere. A lot of people believe that early Mars, on the other hand, was a lot warmer and a lot wetter, and maybe even a harbor for life.
“So, what happened in between? When did this transformation to drier conditions occur? Well, NWA 7034, because of its greater age, may be able to address those questions.”