Its name is Black Beauty, and it has traveled a long way to tell you about its home: Mars.
This meteorite,
discovered in northern Africa, contains preserved materials from the Red
Planet that are 4.4 billion years old, say scientists in a new study
published in the journal Nature. Black Beauty, they say, may be the
first identified example of crust from ancient Mars, and its age
suggests that the planet's crust formed within the first 100 million
years of Mars' existence.
"It's just pressing its
nose against the creation of Mars," lead study author Munir Humayun, a
professor at Florida State University, said of the meteorite.
What's more, the rock
contains 10 to 30 times more water than any previous Martian meteorite,
suggesting it was derived from a water-rich environment, said University
of New Mexico professor Carl Agee, who was not involved in the Nature
research, but separately studies Black Beauty. It is unlike any other
Martian meteorite ever found, he said.
"If I were going to start
looking (for evidence of past Martian life), this would be the first
place I would go, to this meteorite, because it is a sample from the
surface," Agee said.
It's really old, older than we thought
Black Beauty contains
zircon crystal grains that are 4.4 billion years old, according to the
new study. That's only about 100 million years after the solar system's
first dust condensed.
"Since it takes time to
build up a crust, and to allow that crust to process itself until it can
start growing zircons, it's pretty amazing that we have such ancient
zircon," Humayun said.
What's more, said Humayun, the oldest crusts of the Earth and moon formed at around the same time
Although scientists have
found zircons that are almost that old on Earth, only one -- discovered
in Western Australia -- is around the same age. But five zircons in
this Martian meteorite alone -- some of the first zircons to come to
Earth from Mars -- seem to date to 4.4 billion years old.
"A very large portion of the Martian crust must be very ancient," Humayun said.
Humayun's sample of
Black Beauty, officially called NWA 7533, is about the size of a fist,
but all pieces of the meteorite together total about 1.5 kilograms (3.3
pounds).
Earth sees a lot of meteorites generally; about 100 tons of rocks come in from space every day,
said Don Yeomans, manager of the Near-Earth Object Program Office at
NASA's Jet Propulsion Laboratory. But rarely do we find Martian rocks.
Less than 100 have been found, Humayun said.
A large meteor impact on
Mars, about 5 to 11 million years ago, was enough to eject material
from the crust and into space in the form of this meteorite, Agee said.
Cosmic ray exposure measurements suggest it was floating in space for
all this time.
Black Beauty had initially been described in a Science study published in February, led by Agee, which dated it to about 2.1 billion years old.
But since then, Humayun and colleagues found the rock contains
materials that are 4.4 billion years old, and published their new
findings this week.
Agee said his group has independently confirmed Humayun's results regarding the age.
What accounts for this
discrepancy? Agee said his first result may have been for the bulk rock
-- that is, an average age of all of the rock types embedded within it.
It's likely that the earliest formation of the meteorite was at 4.4
billion years, Agee said, but it continued to be shaped by geological
processes for another 2 billion years before it blasted off into space.
Agee and Humayun
continue working on different Black Beauty samples separately, but not
as rivals, said Agee. In fact, they are good friends.
"Two labs working
completely independently coming up with similar conclusions is much more
convincing than if you're all part of the same gang," Agee said.
Different than other meteorites
NASA's most powerful and
sophisticated rover on Mars, the 2-ton Curiosity, has given plenty of
insight into the planet's former habitability since it landed there last
year. But even it cannot do a great job of dating rocks.
On Earth, scientists can
better estimate ages because they can measure the amount of trace
elements in rocks, not just the most common elements. The trace elements
-- those that are present in tiny quantities in a particular sample --
can be more indicative of the processes that led to the formation of
meteorites than common elements, Humayun said.
The trace element
iridium, present in this meteorite, indicates that it came from a
mysterious area of Mars called the southern highlands. That makes Black
Beauty the first known resident of the southern highlands to get to
Earth.
Other samples from Mars
that have reached Earth have been coming from the Martian Northern
Hemisphere, which has low, flat plains. The Southern Hemisphere, by
contrast, has a lot of craters, Agee said, meaning it's about 3.8
billion years old or older.
Given its newly
confirmed age, Black Beauty is one of the oldest samples scientists have
seen from Mars. The other possible contender for that title is the
famous Allan Hills meteorite, which has been dated to a similar time
frame. NASA announced in 1996
that the Allan Hills meteorite, discovered in Antarctica, contained
evidence of primitive life, but that conclusion has since been disputed.
Agee noted futher that the Allan Hills sample is a chunk of bedrock,
and would not have interacted with water and the surface environment the
way that Black Beauty did.
In the meantime,
scientists are also probing Black Beauty for ancient Martian fossils. So
far none have turned up, Agee said, but there could still be chemical
byproducts of primitive life hidden in the rock samples.
Clues to Martian history
Mars had a lot of
volcanic activity when Black Beauty's zircons formed 4.4 billion years
ago, Humayun said. Volcanic processes would have released water, carbon
dioxide and nitrogen, which were trapped inside the interior of Mars,
creating a "a very quick, thick atmosphere, perhaps even an ocean on the
surface."
In other words, we're talking about "very livable conditions" at that time, Humayun said.
"If there was a biosphere on Mars ever, this is the time it would have originated," he said.
Unfortunately for
whatever life may have existed then, these processes happened very early
in the history of Mars. The planet then underwent heavy bombardment by
asteroids and comets, forming the craters in the southern highlands and
knocking the atmosphere and oceans off the planet.
On Earth, a biosphere emerged after our own planet was bombarded, and took advantage of abundant sunlight.
The cold, dry conditions
at the surface of Mars today are so hostile that nothing could survive,
Humayun said. But Black Beauty may hold clues to what might have lived
early in the planet's history.
"We will be looking inside this rock for evidence of early micro-organisms that may have left behind chemical traces," he said.
How it got to scientists
Recovered pieces of the
meteorite, found in 2011, are now the subjects of intensive study. But
they didn't just crash-land on scientists' desks.
A thriving business has
emerged in Northwest Africa among nomads who wander the Sahara Desert
collecting fossils and other interesting rocks and sell them. That's how
Black Beauty first got to a dealer, who sold it to a private collector
in Indiana, who then gave it to Agee to look at.
The rock sat on Agee's
bookshelf for two months. He wasn't even sure that it was a meteorite.
Finally, he decided to cut into it and see what it was.
"It was shiny black on
the outside, and when I cut into it, it was still very black, but it had
also white specks and sparkling specks, and it looked really different
than anything I'd ever seen," Agee said.
The Moroccan dealer who
bought it from nomads called the meteorite "Black Beauty," a name that
has stuck among scientists working on it, Agee said.
Once the word got out
that Black Beauty was from Mars, the nomads scoured for more pieces of
the meteorite, some of which ended up with Humayun.
Any meteorite buff who sees Black Beauty would be "struck by its odd beauty," Agee said.
"It is just a gorgeous
sample," he said. "It's so different. I always say to everybody, 'It's
my favorite meteorite of all time.' "
As scientific investigations continue, researchers may find even more reasons to praise Black Beauty.
source:cnn/elizabeth landau
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