Archive for the ‘Carbonates’ category

Molar Tooth Texture

August 12, 2010

Ok, so remember the weird rock I showed in my Galcier Park geology post? No? Here it is again:

This texture is called “molar-tooth” texture, because apparently someone thought it looked like the teeth of elephants. They must have been studying some weird elephants. It’s a very bizarre texture. It cuts across the layers of the rock as if it is related to fractures, but it is often deformed and squished as if it formed in wet sediment. In some places the minerals filling the fractures are broken up and collected as hard clasts, but it other places they clearly formed after the sediment was deformed.

The two leading explanations for this texture are bubbles and waves*. In the bubble model, the fractures form when gas is evolved in the gooey mud, and builds up enough pressure to propagate through the layers. Then once those voids are formed, fine-grained crystals fill them in. Sometimes, the overlying pressure of newer sediment compressed the voids before they are filled, causing them to accordion up into the contorted shapes we see today. In the wave scenario, pressure changes from powerful storm waves cause the sea floor to undulate, forming the fractures which are then filled in with minerals.

This texture has no modern-day analog because macroscopic life forms disrupt the mud before the mineralization can take place.It’s very unlikely that we would find this on Mars, but it is good practice for us martians to try to explain rocks we’ve never seen before!

*I’m sure I am completely oversimplifying, and likely mangling, these explanations.

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New Deep Sea Vents Discovered in the Caribbean

July 22, 2010

The hybrid robotic vehicle Nereus is recovered after searching for new hydrothermal vents along the Mid-Cayman Rise. Image credit: Woods Hole Oceanographic Institution

Here’s the second of my recent Universe Today Articles: scientists have discovered new deep sea vents in the Caribbean that will teach us more about sunless ecosystems. Good to know if we ever want to look for life in the oceans of Europa some day! Check out the article here.

Spirit Rover Discovers Carbonates

June 4, 2010

Big news from Mars today, Spirit has found evidence for significant amounts of carbonates in the rocks of Gusev crater! Carbonates are really important for two reasons: first of all, Mars has a very thin CO2 atmosphere right now. Too thin for water to remain as a liquid on the surface: it would just boil away and freeze at the same time! But there is lots of evidence that water once flowed on the surface. That means it must have been warmer and the atmospheric pressure must have been higher.¬† A good way to get higher pressure and temperature on the planet would be to have more CO2 in the atmosphere (just take a look at Venus!). But then the question becomes “where did it go”? On Earth a lot of our CO2 is trapped in carbonate rocks like limestone, so the thought was that maybe carbonates could store some of the CO2 on Mars. But until now they have been very hard to find. The Phoenix lander found evidence for a little bit, and orbiting spectrometers have identified some tiny patches that look like carbonates, but this finding by Spirit is much more conclusive.

Carbonates are also important because they dissolve quite easily in acid. The fact that there are rocks on the surface at Gusev Crater that have carbonate minerals in them means that they have not been exposed to much acid, and therefore the environment was much less hostile to life.

I’m going to paste the full press release here, but I also want to note how cool it is that my adviser at NASA, Dick Morris, is the lead author of this study! He does extremely careful and detailed work, so if he is confident enough to publish this finding, I have no doubt that it is true. Congrats to everyone involved on this awesome discovery!

NASA Rovers Finds Clue to Mars’ Past and Environment for Life

The "Comanche" outcrop may be up to one-quarter carbonates. Image Credit: NASA/JPL-Caltech/Cornell University

PASADENA, Calif. — Rocks examined by NASA’s Spirit Mars Rover hold evidence of a wet, non-acidic ancient environment that may have been favorable for life. Confirming this mineral clue took four years of analysis by several scientists.

An outcrop that Spirit examined in late 2005 revealed high concentrations of carbonate, which originates in wet, near-neutral conditions, but dissolves in acid. The ancient water indicated by this find was not acidic.

NASA’s rovers have found other evidence of formerly wet Martian environments. However, the data for those environments indicate conditions that may have been acidic. In other cases, the conditions were definitely acidic, and therefore less favorable as habitats for life.

Laboratory tests helped confirm the carbonate identification. The findings were published online Thursday, June 3 by the journal Science.

“This is one of the most significant findings by the rovers,” said Steve Squyres of Cornell University in Ithaca, N.Y. Squyres is principal investigator for the Mars twin rovers, Spirit and Opportunity, and a co-author of the new report. “A substantial carbonate deposit in a Mars outcrop tells us that conditions that could have been quite favorable for life were present at one time in that place.”

Spirit inspected rock outcrops, including one scientists called Comanche, along the rover’s route from the top of Husband Hill to the vicinity of the Home Plate plateau that Spirit has studied since 2006. Magnesium iron carbonate makes up about one-fourth of the measured volume in Comanche. That is a tenfold higher concentration than any previously identified for carbonate in a Martian rock.

“We used detective work combining results from three spectrometers to lock this down,” said Dick Morris, lead author of the report and a member of a rover science team at NASA’s Johnson Space Center in Houston.”The instruments gave us multiple, interlocking ways of confirming the magnesium iron carbonate, with a good handle on how much there is.”

Massive carbonate deposits on Mars have been sought for years without much success. Numerous channels apparently carved by flows of liquid water on ancient Mars suggest the planet was formerly warmer, thanks to greenhouse warming from a thicker atmosphere than exists now. The ancient, dense Martian atmosphere was probably rich in carbon dioxide, because that gas makes up nearly all the modern, very thin atmosphere.

It is important to determine where most of the carbon dioxide went. Some theorize it departed to space. Others hypothesize that it left the atmosphere by the mixing of carbon dioxide with water under conditions that led to forming carbonate minerals. That possibility, plus finding small amounts of carbonate in meteorites that originated from Mars, led to expectations in the 1990s that carbonate would be abundant on Mars. However, mineral-mapping spectrometers on orbiters since then have found evidence of localized carbonate deposits in only one area, plus small amounts distributed globally in Martian dust.

Morris suspected iron-bearing carbonate at Comanche years ago from inspection of the rock with Spirit’s M√∂ssbauer Spectrometer, which provides information about iron-containing minerals. Confirming evidence from other instruments emerged slowly. The instrument with the best capability for detecting carbonates, the Miniature Thermal Emission Spectrometer, had its mirror contaminated with dust earlier in 2005, during a wind event that also cleaned Spirit’s solar panels.

“It was like looking through dirty glasses,” said Steve Ruff of Arizona State University in Tempe, Ariz., another co-author of the report. “We could tell there was something very different about Comanche compared with other outcrops we had seen, but we couldn’t tell what it was until we developed a correction method to account for the dust on the mirror.”

Spirit’s Alpha Particle X-ray Spectrometer instrument detected a high concentration of light elements, a group including carbon and oxygen, that helped quantify the carbonate content.

The rovers landed on Mars in January 2004 for missions originally planned to last three months. Spirit has been out of communication since March 22 and is in a low-power hibernation status during Martian winter. Opportunity is making steady progress toward a large crater, Endeavour, which is about 11 kilometers (7 miles) away.