Can You Spot the Difference? The Slowly Changing Surface of Mars

Below is a picture taken by the Curiosity Rover on Mars last week.  Had you been on Mars 6000 years ago at this very location what do you think it would have seen?  What differences do yo think you could spot between then and now?

A hillside with thousands of wafer-thin layers of rock on Mars.  Taken by the Mars Curiosity Rover.  Image: JPL/NASA-Caltech 2015

A hillside with thousands of wafer-thin layers of rock on Mars. Taken by the Mars Curiosity Rover. Image: JPL/NASA-Caltech 2015

I have zoomed in on one section of this rock outcrop to show you the fine scale erosion that has taken place.  These thin slabs of rock projecting into the thin martian air are less than 1 cm thick.

A bit closer view of the thin layers of rock that have eroded into sheet of rock that jut out from the rock wall in gravity defying ways.  Image:  JPL/NASA-Catltech

A bit closer view of the thin layers of rock that have eroded into sheet of rock that jut out from the rock wall in gravity defying ways. Image: JPL/NASA-Catltech

How far into the future or past would you have to go to take a picture in which you would be able to readily spot the differences?

The restaurant kids meal activity "spot the differences"  has many android app versions now including this one by ??.   I expect it would take a keen eye to notice the difference in a 6000 year old photograph of Mars and one taken today.

The restaurant kids meal activity “spot the differences” has many android app versions now including this one by CoRa games available at Google Play. I expect it would take a keen eye to notice the difference in a 6000 year old photograph of Mars and one taken today.

I think there is good reason to believe that were you to set pictures taken today beside those taken 6000 years ago you would find it difficult to see any significant differences.

How do we know so little has happened on Mars for thousands of years?  The Curiosity Rover is providing evidence that strongly points us to this conclusion. It has provided, through some clever methods detailed below, the first rough estimate of both the age of some martian rocks and the rate of erosion.  So how fast have rocks been eroding on Mars in the past 6000, 100,000  or even millions of years?  In this part of Mars measurements have been taken that reveal that these rocks are only eroding at a pace of a 1/2 inch per thousand years.

The only erosive forces active at this site are wind, thermal contraction and expansion and possible some chemical weathering.  None of these forces can work quickly in the thin, cold atmosphere lacking in many chemically active molecules.  Under present conditions measured directly by the Curiosity Rover, erosion at 1/2 inch per thousand years seems almost too optimistic.  You might wonder though, but couldn’t conditions thousands of years ago have been different.  Yes, it is possible but the Curiosity Rover has provided data that point us to the conclusion that current conditions have persisted well into the past on Mars.  About a year ago I wrote a post in which I reported how the erosion rate on Mars has been estimated from data collected by Curiosity. I have appended that post to this one.

Mars Geology in the Context of Young Earth Creationism

Literal-day young earth creationists such as Ken Ham of Answers in Genesis believe that not only is Earth less than 10,000 years old but the entire universe is also young.  They are YUCs (young universe creationists).   When they look at these layered rocks on Mars what is their response?

Faced with the increasing evidence of massive amounts of sedimentary rock on Mars, YUCs are quickly adopting a catastrophic recent origin of geological features of the planets including Mars.  They accept the evidence that water once flowed on Mars.  They can see that there are massive deposits of sedimentary rock, there are erosion patterns that suggest large rivers and there are shallow areas that have rock types that point to their formation in shallow oceans or lakes. For example here is Answer in Genesis’ Andrew Snelling in 2007:

“There is no longer any doubt that the surface of Mars has in the past been covered by huge volumes of water which spread over vast areas. These resulted from cataclysmic outflows, which were also responsible for catastrophic erosion of channels and valleys, on a scale far greater than anything comparable on Earth, and deposition of sedimentary strata.”  Water activity on Mars: Landscapes and Sedimentary Strata.

I wrote about this earlier this year (Global Flood on Mars: Where Did the Water Go?).  YUCs recognize that current rates of deposition and erosion cannot explain the present-day observed features of Mars so they invoke a catastrophic past.  You may wonder though, why not simply invoke Creation? Why not say that God created just what the Curiosity rover is seeing today as it is?  This is what is called creation with the appearance of age and YUCs rightly resist claiming that God simply created all this evidence of a past history of Mars.  But being bound to origins view that requires Mars to be very young forces them to find alternative explanations for the evidence of massive changes to the geological landscape of Mars.   Hence, the appeal to Noahic-like catastrophic conditions in the very recent past.

While it is very likely that past conditions were very different from those present on Mars today, there is no evidence to support those conditions having been different in the very recent past.  A crater, filled with sediments that have then eroded to form the valleys we see today speak to diverse conditions in the past but spread over long periods of time. The conditions that allowed for the unique appearance of the rock formation we see today are clearly those of long periods of wind erosion.    How long, probably hundreds of millions of years of erosion at rates similar to those observed today as evidenced by the data collected by the Curiosity Rover (see reposted material below).

Let me suggest one last observation that supports the conclusion that Mars has not changed much over thousands of years.  Mars has been called the red planet for 4000 years.  The very fact that it has been observed to be red for that long tells us that the planet has been devoid of water and covered in red dust for that long. Hence, wind erosion has been the only significant game in town with respect to erosion. Had there been a huge flood there 4500 years ago as YUCs propose then there would be massive amounts of water vapor in the atmosphere following that flood and the planet would not appear red from afar.

A repost of my March post:

Global Flood on Mars: Where Did the Water Go?

Just how fast are some rocks on Mars eroding?  A few months ago I asked a Martian rock that question (see: My Interview with a Martian: A Story of Origins) and I was not given a very satisfying answer.  Well, that rock can be excused for being a bit confused about time given how boring it may be sitting on the surface so long with so little to do.   But now we have sent a little rover called Curiosity to Mars to do some further investigations for us. That rover has some sophisticated analytical equipment on board. One of them can take drilled rock dust, heat it up until it melts and the smell the molecules that emanate from the melting crystals.  What we learned this week is that some of the molecules that this instrument can measure are the kind that can be used to calculate radiometric ages.  The precision of this instrument is not like we have in labs here on Earth but nonetheless it’s an impressive achievement and gives us our first direct test of age of rocks and allows to even infer rates of erosion of rocks.

On sol 279 (May 18, 2013), Curiosity drilled at a second site, named Cumberland. NASA / JPL / MSSS / Emily Lakdawalla

On sol 279 (May 18, 2013), Curiosity drilled this hole at a second site named Cumberland.  Notice that the rocks are not  red or orange inside but rather a grey color. The “red” planet results from a layer of iron-rich dust that coats the surface. 
NASA / JPL / MSSS / Emily Lakdawalla

The first measurement reported in a paper entitled In Situ Radiometric and Exposure Age Dating of the Martian Surface published in Scienceprovided a K-Ar radiometric age for the rocks that make up the original rocks of the Gale Crater area.  That measurement yielded an age of 4.2 billion years give or take a few hundred million years.  This is on par with the oldest rocks on Earth and was the age predicted for this region of Mars based on relative methods of dating such as crater density counts.

Curiosity took this photo from Yellowknife Bay, looking west-northwest up a series of scarps created by wind erosion. NASA / JPL / MSSS

Curiosity took this photo from Yellowknife Bay, looking west-northwest up a series of scarps created by wind erosion.  The Sheepbed mudstone was drilled and chemically analyzed.   There results of that analysis and others provide strong evidence that this area was a lake.  There are some layers that are different in composition making them harder and so more resistant to erosion. This is the reason why there are various ledges formed here as wind eroded the rocks.
NASA / JPL / MSSS

That date was expected but what was really interesting and relevant to the first question I posed is that they didn’t just measure the origin of the material in the rocks but they also produced a date of when a particular set of rocks came to be exposed at the surface.   The whole area you see in the pictures above and below is thought to have been buried under many layers or rock which have been eroded over time to reveal the layers that we are seeing today. 

Emily Lakdawalla reviews the significance of the dates. If you want to know everything that is happening in planetary science I highly recommend following her on Twitter (@elakdawalla).   In her recent blog post “Curiosity results at AGU: Gale crater rocks are old, but have been exposed recentlyLakdawalla explains how the length of time a rock has been exposed at the surface can be calculated:

Mars lacks a significant magnetic field, so anything on its surface is exposed to bombardment by galactic cosmic rays. Galactic cosmic rays can produce specific isotopes of noble gases: argon-36, neon-21, and helium-3. These gases would not have been present in the rocks when they first formed, so if you know the rate at which the isotopes are produced on Mars, and if you measure their abundance in current rocks, you can estimate how long the rock has been exposed at, or near, the surface.

Schematic illustration of the exhumation of boulders from a heterogeneous deposit by erosion of the matrix.  Think of this as bouders in a glacial deposit.  As the material around the bouders erodes it leaves the boulder at the surface.  By measuring the ratio f nuclides in the surface of each of these rocks in the last frame it is possible to tell which boulder was uncovered first  because it will be the one that has been exposed to cosmic rayes the longest and so will be the most altered.  Similarly layers of rock on Mars can be tested and rocks in one area to find out if they might have been exposed longer than in other areas.  After Zreda et al. (1994)

Schematic illustration of the exhumation of boulders from a heterogeneous deposit by erosion of the matrix. Think of this as boulders in a glacial deposit. As the material around the boulders erodes it leaves the boulder at the surface. By measuring the ratio of nuclides in the surface of each of these rocks in the last frame it is possible to tell which boulder was uncovered first because it will be the one that has been exposed to cosmic rays the longest and so will be the most altered.  From the differences in the dates of the rocks a rate of erosion of the matrix material can be estimated.  Similarly layers of rock on Mars can be tested and rocks in one area to find out if they might have been exposed longer than in other areas. After Zreda et al. (1994)

A form of this analysis can be done for rocks on Earth as well.  It is called cosmogenic nuclide dating and it allows for rough estimates of the rates of erosion, or exposure times, in different locations (eg. how fast are rocks eroding in Utah vs deserts in other places in the world).    So what can we learn about erosion on the surface of Mars from this form of analysis? Lakdawalla goes on to explain:

You can imagine how the relatively weak mudstones of the Sheepbed Unit are getting sandblasted away by wind scouring, and that’s undercutting the more resistant layers like Gillespie Lake. In other words, the Sheepbed rocks are being exposed by a process of scarp retreat. Assuming that this is a continuous and ongoing process, if you follow the direction of the wind, then, until you get to the scarp, that’ll take you to Sheepbed rocks that should be freshly exposed. You can estimate the rate of scarp retreat, and it’s about 1 meter per million years.

I think the operators of the Curiosity rover have come up with a pretty nifty way of estimating erosion.  The 1 meter per million years is a very rough estimate so maybe it is only ½ meter or 2 meters per million years.  Regardless, this suggests that erosion really is happening on Mars. You might think that 1 meter of rock erosion in 1 million years is a very very slow pace but remember the atmosphere is very thin on Mars and there is only wind and freeze/thaw cycles as the primary forces of change on the surface.

Our martian friend hanging out on the surface slowly eroding in the wind.  The Curiosity rover snapped this image while driving by. Image: JPL/NASA-CalTech

Our martian friend hanging out on the surface slowly eroding in the wind. The Curiosity rover snapped this image while driving by. Image: JPL/NASA-CalTech

Back to our martian friend laying there on the surface (see picture to the right). In my interview (My Interview with a Martian: A Story of Origins) I asked this rock what would happen to him in the future? This was his reply:

Well, assuming you don’t poke me or shoot me with your little laser toy on your way by (referring to the Curiosity Rover obviously), I expect that I will continue to hang on for at least 10,000 more years but possibly several hundred thousand years or so after which I will probably have completely fallen apart into all those small stones that I was originally made of.  Now those parts are much tougher than I was and wind and thermal tension won’t be able to tear them down so quickly so someday you will probably find a little pile of stones here spread out a bit as they are pushed slightly by the wind and sand over time.  On the other hand, it is possible that another meteorite could hit near here and cover me with a blanket of rocks in which case those new friends would shield me from erosion and I might live for millions of years to come.

The prediction of 10,000 years or a bit longer seems about right given these new estimates of the rate of erosion. I had thought maybe he could last another million years but apparently erosion is occurring at a faster pace than I would have guessed.  Still, this little rock is but a very small piece of the geological terrain in the area that includes many small meteor craters and many hundreds of meters of rock that have been eroded in the area before our little friend even came to find his way to his present location.

Gale crater overview with age estimates.

Gale crater overview with age estimates.  Image: JPL/NASA-Caltech

The Curiosity rover science team has now collected enough evidence to convince them the rover is now driving around on rock that was deposited originally as sediments in a large lake.  But that lake has been dry for hundreds of millions of years if not billions of years.  Since then massive amounts of rock have eroded and small new craters have been created and eroded and then covered with even more debris from other cratering events.  All the while wind has been slowing eating away at the rock surfaces and moving material from one place to another.  If we took a snapshot today and came back one million years from now it might look very similar but in many subtle ways the landscape is constantly changing.  It a dynamic planet but it’s a slow motion dynamism that we are seeing.

This picture was taken two days ago by the Curiosity rover. In the distance is the hopeful destination.  This area is where scientists believe an ancient lake once was.  There should be a lot to look at and test when they get there.  Image: JPL/NASA-CalTech

This picture was taken two days ago by the Curiosity rover. In the distance is the hopeful destination. This area is where scientists believe an ancient lake once was. There should be a lot to look at and test when they get there. Image: JPL/NASA-CalTech

Featured image:  Animal Spot the Difference Android App by CoRa Games

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  1. […] seen a lot of layered rocks on the surface of Mars, like these amazing rocks captured in July, 2015.Read more about this image. Credits: […]

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