A little-known fact is that each year Earth is hit by by half a dozen or so one-pound or larger rocks that were blasted off the surface of Mars by large impacts and found their way into Earth-crossing orbits. Nearly 10% of all rocks blasted off into space from the Red Planet end up crashing into Earth. Over the history of the Earth, billions of football-sized rocks have landed on its surface, some only slightly heated by the launch, reaching Earth in a matter of a few months.
By directing energy beams at tiny crystals found in a Martian meteorite, a Western University-led team of geologists has proved that the most common group of meteorites from Mars is almost 4 billion years younger than many scientists had believed – resolving a long-standing puzzle in Martian science and painting a much clearer picture of the Red Planet's evolution that can now be compared to that of habitable Earth. The geologists studied a group of meteorites known as shergottites that unlike most Martian space rocks that tend to be very old, are generally thought to be remarkably young — forming as a result of volcanic activity about 150 million to 250 million years ago, around the same time that dinosaurs dominated during Earth's Jurassic period. The shergottites are a sign that Mars might have been geologically active fairly recently, and thus perhaps still harbors some form of life.
If there is still life on Mars it could be thriving underground with the heat energy provided by volcanism. Butif there haven't been any active volcanoes 4 billion years the odds that there was life left on Mars are slim.
In a paper published in the journal Nature, lead author Desmond Moser, an Earth Sciences professor from Western's Faculty of Science, Kim Tait, Curator, Mineralogy, Royal Ontario Museum, and a team of Canadian, U.S., and British collaborators show that a representative meteorite from the Royal Ontario Museum (ROM)'s growing Martian meteorite collection, started as a 200 million-year-old lava flow on Mars, and contains an ancient chemical signature indicating a hidden layer deep beneath the surface that is almost as old as the solar system.
The team, comprised of scientists from ROM, the University of Wyoming, UCLA, and the University of Portsmouth, also discovered crystals that grew while the meteorite was launched from Mars towards Earth, allowing them to narrow down the timing to less than 20 million years ago while also identifying possible launch locations on the flanks of the supervolcanoes at the Martian equator.
More details can be found in their paper titled, "Solving the Martian meteorite age conundrum using micro-baddeleyite and launch-generated zircon."
Moser and his group at Western's Zircon & Accessory Phase Laboratory (ZAPLab), one of the few electron nanobeam dating facilities in the world, determined the growth history of crystals on a polished surface of the meteorite. The researchers combined a long-established dating method (measuring radioactive uranium/lead isotopes) with a recently developed gently-destructive, mineral grain-scale technique at UCLA that liberates atoms from the crystal surface using a focused beam of oxygen ions.
Moser estimates that there are roughly 60 Mars rocks dislodged by meteorite impacts that are now on Earth and available for study, and that his group's approach can be used on these and a much wider range of heavenly bodies.
"Basically, the inner solar system is our oyster. We have hundreds of meteorites that we can apply this technique to, including asteroids from beyond Mars to samples from the Moon," says Moser, who credits the generosity of the collectors that identify this material and make it available for public research.
In 2009, a study by a team of scientists of a meteorite that originated from Mars revealed a series of microscopic tunnels that are similar in size, shape and distribution to tracks left on Earth rocks by feeding bacteria. Although the researchers were unable to extract DNA from the Martian rocks, the finding nonetheless adds intrigue to the search for life beyond Earth.
Martin Fisk, a professor of marine geology in the College of Oceanic and Atmospheric Sciences at Oregon State University and lead author of the study, said the discovery of the tiny burrows do not confirm that there was life on Mars, nor does the lack of DNA from the meteorite discount the possibility.
"Virtually all of the tunnel marks on Earth rocks that we have examined were the result of bacterial invasion," Fisk said. "In every instance, we've been able to extract DNA from these Earth rocks, but we have not yet been able to do that with the Martian samples.
"There are two possible explanations," he added. "One is that there is an abiotic way to create those tunnels in rock on Earth, and we just haven't found it yet. The second possibility is that the tunnels on Martian rocks are indeed biological in nature, but the conditions are such on that the DNA was not preserved."
More than 30 meteorites that originated on have been identified. These rocks from have a unique chemical signature based on the gases trapped within. The noble gas trapped in glass in the meteorites serve as a "fingerprint" that matches the composition of the Maritian atmosphere measured by the Viking Mission spacecraft that landed on in 1976. These rocks were "blasted off" the planet when was struck by asteroids or comets and eventually these Martian meteorites crossed Earth's orbit and plummeted to the ground.
One of these is Nakhla, which landed in Egypt in 1911, and provided the source material for Fisk's study. Scientists have dated the igneous rock fragment from Nakhla – which weighs about 20 pounds – at 1.3 billion years in age. They believe that the rock was exposed to water about 600 million years ago, based on the age of clay found inside the rocks.
"It is commonly believed that water is a necessary ingredient for life," Fisk said, "so if bacteria laid down the tunnels in the rock when the rock was wet, they may have died 600 million years ago. That may explain why we can't find DNA – it is an organic compound that can break down."
Fisk and his colleagues have spent more than 15 years studying microbes that can break down igneous rock and live in the obsidian-like volcanic glass. They first identified the bacteria through their signature tunnels then were able to extract DNA from the rock samples – which have been found in such diverse environments on Earth as below the ocean floor, in deserts and on dry mountaintops. They even found bacteria 4,000 feet below the surface in Hawaii that they reached by drilling through solid rock.
In all of these Earth rock samples that contain tunnels, the biological activity began at a fracture in the rock or the edge of a mineral where the water was present. Igneous rocks are initially sterile because they erupt at temperatures exceeding 1,000 degrees C. – and life cannot establish itself until the rocks cool. Bacteria may be introduced into the rock via dust or water, Fisk pointed out.
"Several types of bacteria are capable of using the chemical energy of rocks as a food source," he said. "One group of bacteria in particular is capable of getting all of its energy from chemicals alone, and one of the elements they use is iron – which typically comprises 5 to 10 percent of volcanic rock."
Another group of OSU researchers, led by microbiologist Stephen Giovannoni, has collected rocks from the deep ocean and begun developing cultures to see if they can replicate the rock-eating bacteria. Similar environments usually produce similar strains of bacteria, Fisk said, with variable factors including temperature, pH levels, salt levels, and the presence of oxygen.
The igneous rocks from are similar to many of those found on Earth, and virtually identical to those found in a handful of environments, including a volcanic field found in Canada.
One question the OSU researchers hope to answer is whether the bacteria begin devouring the rock as soon as they are introduced. Such a discovery would help them estimate when water – and possibly life – may have been introduced on Mars.
The image at the top of the page shows two Martian volcanoes rising above a crater-studded landscape that sit side by side in the red planet's northern hemisphere. This image from the European Space Agency's Mars Express orbiter maps contrasting elevations in the region, from the elongated Rahe crater in violet up to the grey summit of the higher volcano Ceraunius Tholus, which rises 5.5 kilometres high and spans 130 kilometres across, dwarfing its neighbour Uranius Tholus.
The Daily Galaxy via Nature, LA Times, and Oregon State University
Image credit: ESA/DLR/FU Berlin (G. Neukum)