Mt Sharp (Aeolis Mons) is a geologist’s dream. Following on from a recent post, Why Gale Crater, I thought it would be interesting to examine this photo by Curiosity from within Gale Crater, looking at the Mons.
The numbers on this image show the distance from the rover as it looks out across the valley within the crater at Aeolis Mons. The small inset image is of a large rock, roughly the size of the Mars Curiosity Rover, some nine kilometres (roughly 5.5 miles) away, allowing us to gain some perspective on size. The triangular, pointy mound this rock sits in front of is approximately 300 meters (1000 feet) across and 100 meters (300 feet) high.
This image shows sedimentary layers spanning several billion years of history on Mars. Look at the beautifully delineated layers or strata on the Mons. Each layer accumulated over tens to hundreds of millions of years before being eroded away by the Martian weather, leaving the view we see today.
On Earth, we find fossil beds captured chronologically in sedimentary layers that are then exposed by the kind of weathering we see on Mars. That’s not to say we’ll find fossils on Mars, but if life has existed in other Martian epochs, this is where we are most likely to find it.
Not only do geological features on Earth contain fossils, some of them are comprised almost entirely of fossils, like the White Cliffs of Dover. These magnificent cliffs are the fossilized remains of prehistoric single-celled algae which decayed to form chalk a hundred million years ago during the Cretaceous period. At upwards of a hundred meters in height, these cliffs represent the gradual accumulation of sediment over roughly 35 million years.
In Texas, the Capitan mountains in Guadeloupe National Park are another fascinating example of how radically landscapes can change over immense geological time periods.
Somewhat counter-intuitively, this prominent mountain is the remains of a submerged reef dating back to the Permian era, some three hundred million years ago. If these kind of transformations are possible on Earth, imagine what has happened on Mars over the same span of time.
Looking at our image from Curiosity, the 10 kilometre mark on Mount Sharp reveals several contrasting layers, thick dark bands separate several lighter strata, marking vastly different types of rock. This suggests significant differences in the prevailing climatic conditions over millions of years during their formation. Mount Sharp is a time machine, revealing the history of Mars in distinct epochs, showing how the planet has been radically reshaped over time. Mars is anything but static like the Moon. To look at Mars as a cold, dry, dusty, lifeless desert is a gross oversimplification.
One thing NASA will be looking for with Curiosity is graded bedding. If there are several layers of progressively graded rocks, from large to small, then from large to small again, we can be confident these layers were deposited in water at different times, where the coarse stones settle below the fine grains time and again, perhaps during major floods separated by dry periods.
Sedimentary systems are, by definition, built by the flow of material from highlands to low. They are normally carried by liquid, but the wind can play a part as well.
In the case of Mt Sharp, the lowest areas you can see in this photograph are the oldest sedimentary layers, but they’re buried by recent erosion. The higher, relatively more recent layers are still hundreds of millions to billions of years old, as it would take considerable time for all of these layers to have formed, then to have eroded away to reveal the landscape we see today.
Looking at Mount Sharp, it is interesting to note that the layers visible in this image are all parallel, meaning in this local area at least, there has not been any of the tectonic upheaval we see on Earth. Given the lack of a major satellite flexing the Martian crust like Earth’s moon, this is not surprising.
Serious consideration has been given to Valles Marineris, the Grand Canyon of the Solar System, being the result of tectonic activity, but there are no plate boundaries, making this unlikely. There are also theories that describe both the Valles Marineris and the Tharsis Uplift as being the indirect result of the impact that formed the Hellas basin, but that’s a fascinating discussion for another post.
Geology is more than just the study of rocks, it is the study of history on the grandest of scales, and how history has been written into the very rocks of a planet. On Earth, rocks record the chronological impact of life on the planet, perhaps the same is true of Mars. With Curiosity on the ground, Martian geology has been given a whole new impetus. The results of this exploration are sure to be enlightening.