quinta-feira, 5 de dezembro de 2013

Scientist discovers ancient crust from Mars

Using measurements as small as a soil sample from a meteorite, Florida State University researchers led by Dr. Munir Humayun, a professor in the university’s Department of Earth, Ocean and Atmospheric Science, has discovered and began testing what is considered the first example of ancient crust from Mars.

Dated to be about 4.5 billion years old, the rock, named NWA 7533, is believed to hold valuable information regarding Mars’ crust. This rock from a crater was found by a group of Bedouin tribesmen in the Sahara Desert.

“The Bedouin tribesmen of the Sahara desert roam the desert freely and are intimately acquainted with the rocks and minerals of their dry environment,” Humayun said. “In the past three decades they have discovered a market for meteorites with U.S. and European private collectors who pay handsomely for the haul of treasure brought to Moroccan dealers. I don’t know all the details, but the famed meteorite, nicknamed Black Beauty, was purchased from a dealer in Erfoud, Morocco. The dealer had as many as five stones all from the same fall totaling about one and a half kilograms (about three pounds) that were found scattered across the desert floor.”

With this rock now in the possession of FSU researchers, they are looking forward to gaining new insight into the crust of the Red Planet in the scientific community.

“To a geochemist, rocks are like books that are read with a laser to tell their complex stories. This meteorite is like a book with thousands of pages. It told us that the crust of Mars was assembled very early in the planet’s history. Since the crust-building volcanoes burp out water vapor and other gases that form the atmosphere, oceans and earliest life, this is very significant,” Humayun said. “It lends support to the idea of a warm, wet early Mars. We also found Martian soil lumps in the meteorite identical in composition to that measured by spacecraft and rovers at Gusev Crater on Mars. There was only one set of properties that modern Martian soils and these ancient soil lumps did not share.”

If there was an early Martian biosphere, then this rock was likely to have witnessed the microbes.

Humayun’s team includes FSU undergraduate and graduate students. He involves them in various aspects of his research spanning both terrestrial and extra-terrestrial geochemistry. He spends his time teaching both undergraduate and graduate courses, mentoring Ph.D and master’s degree students, and postdoctoral fellows. His research is conducted at the National High Magnetic Field Laboratory, which he says is the best place he has “ever worked in terms of infrastructure support and a wonderful staff.”

“I came to FSU ten years ago as an associate professor because of the excellent geochemical group at the National High Magnetic Field Laboratory. Prior to that I taught at The University of Chicago, where I received the Quantrell Award for Excellence in Undergraduate Teaching,” Humayun said. “I started in Geochemistry with an interest to combine my skills in chemistry, and my interests in nuclear physics with Earth and Space Science. There were excellent Geochemistry facilities and very competent faculty in that area by which I was drawn to Geochemistry.”

With students, faculty and researchers ready to study this rock, they are beginning to uncover important new information about Mars’ ancient crust.

“Importantly, Mars’ surface is covered with two very distinct types of crust: the southern highlands are heavily cratered and therefore very ancient, the northern plains are smooth and have many fewer craters,” Humayun said. “Craters are like wrinkles on people - the more they have the older they appear. A heavily cratered landscape is covered with a rock type known as a breccia–a mixture of many broken fragments of rocks from the repeated hammering by meteorites. These rocks should contain high levels of the element iridium and other elements like it from the meteorite hammers that pounded the ancient Martian surface. This is exactly what we found when analyzing this unusual meteorite. It was a breccia and it was loaded with meteoritic debris containing iridium and nickel.”

Some findings by Humayun and his group are potentially turning what some scientists and researchers thought they knew about the ancient Martian crust upside down.

“Many researchers have long thought that Mars was once intensely melted by large impacts. Our data is inconsistent with this idea termed a magma ocean,” Humayun said. “Evidence for past magma oceans have been found on the Moon, and inferred on Earth, Mars and Mercury, and likely on all major bodies in the inner solar system. Our data on this Martian meteorite, one so ancient it should bear witness to the magma ocean, implicates a cooler growth of Mars, sufficient to melt slightly but no single, large impact sufficient to melt the entire surface of the planet. The idea has strong adherents but our work may change minds.”

Another surprising finding is that using this rock from the meteorite, the rock was able to be dated and found to be a part of the crust that formed around the same time as the crust of the moon and Earth.

“The ages of the zircon minerals in this piece of Martian crust are as old as the oldest zircons recorded from the Earth and Moon,” Humayun said. “What’s surprising is how many such old zircons were found in this Martian meteorite compared with zircons from the Moon and Earth of equal antiquity which are harder to find (and we have so many more rocks from these bodies that have been searched). This implies that Mars’ crust developed very early and that the southern highlands have not been significantly changed over the eons of geological time.”

Humayun and other FSU researchers are making positive steps in discovering information on the origin and age of the ancient Martian crust, and are continuing to find out as much as they can about the Red Planet.

Source: fsunews.com

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