Curiosity has beamed back some really remarkable images from Mars in the past couple of days. The site for its landing was chosen because it appeared from satellite images that there was layered rock and some diversity of chemical signatures at different elevations but the pictures taken from ground level reveal a more spectacular and complex geology that I think anyone could expect. I reviewed some of the very first images from Curiosity rover in an earlier post but now want to take a closer look at some of the diverse landscapes on Mars that we are seeing close up for the first time. Below are several images taken of portions of Mt. Sharp and one of the satellite scans of the same area. The rock layers in these views that are still from more than 10 kilometers away but the number already visible is really amazing. Of course the NASA marketing of this location has been all about the potential to find rock layers that were deposited either in a shallow lake or small floods and thus could harbor some chemical signatures of past life. All that talk makes it seem like this is all the mission is about. It is far more than that! I don’t really find the life angle all the interesting but I do find the geology to be fascinating and this is about as good as it gets in terms of a great geological mystery: a set of really interesting hypotheses to explain the origin of Mt. Sharp and a rover with instruments that should be able to collect the type of data that will test those hypotheses. This location is both beautiful but challenging to understand.
Lets take a look as some of the features of Mt. Sharp and then a quick look at the hypotheses for its origins. For now this is just a review of conventional geological ideas without much commentary on what this mountain tells us about the age of the Earth/solar system. In the next post on Mars I want to discuss how young earth creationists might respond to this geological formation on a another planet but for now think about how you might answer the question: when did these rocks form?
The background again: Curiosity has landed in Gale Crater which is 155 kilometers (96 miles) in diameter with a 5 kilometer high mountain called Mt. Sharp, near the center that from orbit (see image below – click for very large view) appeared to be made of layered sedimentary material rather than basalts (volcanic rock) suggesting it is a product of material deposited into the crater after its formation. (1,2)
Whence Mt. Sharp? Now look at the first image above which is a just of the “foothills” of Mt.Sharp. This false color image clearly shows very distinct horizontal bands of sedimentary rock. These are the rock layers that some geologists say have signatures of clay-type minerals which could be a signature of the interaction of water with the sediments at some point. Ok, that’s fine and it sure looks just like layers of rock on earth that are formed in water in a shallow lake or bottom of the ocean. But, consider that these rocks are exposed on the flanks of a mountain inside of a very deep crater which is one of the lowest elevation sites on Mars. It is easy to image the crater being filled with water flowing from higher ground to the south and resulting in thousands of meters of layered sediments. But then how did all the sediments surrounding this huge mountain get removed from the crater again to form a 5 kilometer deep basin around that mountain!? That is part of the geological mystery of this site. One hypothesis, and seemingly the one that NASA is most interested in testing, is that over time wind has eroded all this material as the edges of the crater created a vortex resulting in the center not being eroded as quickly as near the edges. In addition, during this process maybe the upper layers of the mountain are layers of dust piled up from wind creating a taller mountain than the surrounding area? So the mountain could be combination of many layers sediments from liquid water deposition topped off with layers of dust deposited during the erosion of the surrounding material.
You should be asking yourself about now, if that really happened that is a lot of erosion! So how long would that have taken? Did these layers form thousands, millions or hundreds of millions of years ago and then how long did this process of wind erosion occur to form the mountain and hills we see today? The suggestion is that bottom layers formed 3.5 to 4 billion years ago and the mountain was formed by erosion into is present appearance over the next couple billion years and probably has looked pretty much like it does today for up to a billion years. Why so long ago? Simply put this crater itself is thought to be very old as it lies in region of the Mars that has many craters and this crater has craters inside the crater from more recent impacts. Those impacts must have occurred after all these sediments were formed and the erosion of the sediments took place.
Now look at this image above. From this view we get more information and what we see suggests an ever more diverse geological history than the first image. The white dots represent the boundary of two distinct sets of rock formations. If you click for a large view it will be obvious that the layers below the white dots are essentially horizontally layered rocks like those of the first image. But above those horizontal layers there are hundreds of meters of layers rock that are NOT horizontal but are dipping down and then meet that dotted line. Where these layers meet we would call this a geological unconformity on earth. The layers above appear to be deposited in a very different fashion and have a different composition, as suggested by the different color, than those below. Then look in the upper left hand corner. Higher up on the flanks of Mt. Sharp are what appears to me to be another set of layers rocks that are again more horizontal. Wow! This is really an amazing set of rocks. On earth this would require a diverse set of geological phenomena to explain.
If this was just a case of deposition in a lake we would not see this type of unconformity and since some form of uplift is unlikely without disrupting the layers below an explanation for the dipping layers is needed that probably doesn’t require liquid water. Such an explanation for the origin of Mt. Sharp has already been proposed even before Curiosity landed. In a paper by Edwin et al submitted recently (you can see the entire paper HERE), the authors examine the layers from images taken from orbit and they hypothesize that aeolian (wind) processes are the primary causative agent of Mt. Sharp’s formation. Using modeling of wind velocities and information about past climate changes (see reference 5) they suggest that the rock layers that are observed are not the result of deposition in water but rather are the result of many thousands of repetitions of ice ages on Mars combined with down-slope winds in this large crater. How this would work is that when the climate changes on Mars due to the known and measured wobble on its axis of rotation (the Earth also wobbles causing changes in climate over time) water from the poles released and builds up in the form of ice a lower altitudes. There is a growing body of evidence that there was large patches of ice much further south than seen today. (2) It is proposed that ice formed primarily in the center of the crater and then dust got trapped in that ice and deposited on top of it. When the climate changed again and the ice sublimated back into the atmosphere the dust layer would be left creating a layers of new soil/dust. At the same time it is also possible that some water melted and then leached chemicals down into the lower layers of the sediments resulting in the different chemical profiles seen today. The main point is that successive “ice ages” would have resulted in the pancaking of many many layers of dust on top of one another resulting in the layering of sediments. Depending on the source of the dust wand what what other formations were eroding at the time, the dust would have different chemical signatures. At some point the wind patterns of Mars may have changed and the ice ages may have differed in their intensity causing the dust and layers to accumulate in a different pattern resulting in the unconformity. How long would this take? These “ice ages” are thought to have come and gone every 5 million years or so as predicted by the wobble of Mars. (5) If each layer represents one of these ice ages then the mountain represents hundreds of millions of years of development.
Effectively what you could be looking at in this picture is a pile of accumulated dust 5000 meters tall! Nothing like that on Earth. If the Curiosity rover finds that the layers are made of all small particles consistent with Mars dust this will be strong evidence in support of the ice age/dust hypothesis and liquid water mediated sedimentation processes were not likely responsible for these layers. If there is a large mixture of pebbles, rocks and dust that are sorted into layers then an origin by water transport would be more likely. The curiosity rover is going to be able to test these competing hypothesis as it gets closer and eventually examines the chemistry of the rocks in the lower layers. If this latter hypothesis of ice and dust causing all the layers is upheld by further observations it could well be that this entire mountain is just a pile of accumulated dust and thus chance of finding evidence of life here would be greatly reduced. In reading about these models I found the evidence from wind, Mars wobble rotation and resulting climate changes, analysis of the layers from orbit (ref 1 and 3) and the first pictures of the mountain to be more convincing than the watery origin that NASA is often found promoting. If your definition of success or failure of the mission is bound solely to the idea of finding conditions that would promote life I expect that failure is what lies ahead for you. Since my anticipation for the exploration is not centered around the question of life, I find the mission to be incredibly interesting and look forward to years of other worldly images for me to gaze upon. Truly God has given us unending wonders to explore.
Obviously all of these explanations for the origin of Mt. Sharp employ massive time scales. Whether wind or water are the primary agents of producing this geological formation the time scales necessary really boggle the brain. That this picture that was taken by Curiosity could have been taken a million years ago and looked nearly identical to what is seen today aside from some sand dune shifting is really hard to wrap ones brain around. But the physics is quite objective in terms of the requirements for moving this much material over time. In the next post I will lay out all the possible origins of this formation including possible hypotheses that young earth creationists might put forward to explain this diverse landscape within the limits of 10,000 years or less.
1. http://authors.library.caltech.edu/17685/1/Milliken2010p7213Geophys_Res_Lett.pdf - this is a a link to an article details the layers in gale crater as determined from orbit. This article should be accessible by to everyone.
2. R. E. Milliken, J. P. Grotzinger, and B. J. Thomson. Paleoclimate of Mars as captured by the stratigraphic record
in Gale Crater. GEOPHYSICAL RESEARCH LETTERS, VOL. 37, L04201, doi:10.1029/2009GL041870, 2010
3. http://arxiv.org/ftp/arxiv/papers/1205/1205.6840.pdf This article appears to be a manuscript link to a submitted article this year. This shows how modeling was used to suggest how mounds could “grow” in the center of craters by the action of wind vortexes and successive ice layer growth and retreat. Growth and form of the mound in Gale Crater, Mars: Slope-wind enhanced erosion and transport. By, Edwin S. Kite, Kevin W. Lewis, Michael P. Lamb
4. Thomson, BJ, NT Bridges, … and GM Marion. 2011. Constraints on the origin and evolution of the layered mound in Gale Crater, Mars using Mars Reconnaissance Orbiter data. Icarus, Vol 214 (2). 2011. PP 413-432.
5. http://arxiv.org/pdf/1102.0868.pdf This is a submitted manuscript by Brasser, R and KJ Walsh. 2011. Stability analysis of the Martian obliquity during the Noachian era. Astrophysics.
6. ORIGIN AND EVOLUTION OF SEDIMENTS IN GALE CRATER THROUGH ICE-HOSTED PROCESSES. 2012. P. B. Niles1 and J. Michalski. 43rd Lunar and Planetary Science Conference (2012)