We went downhill and we went into a big topographic basin that kind of remind, reminded us of, of Moab, Utah. It looks like the kind of place you want to get your mountain bike and go for a cruise. Lots of bedrock. The bedrock is layered, which was very important to us. So you can see in the background there are thin horizontal layers that go along. Those are the ones that we were after. And so we drove downhill through what we knew was ancient river deposits. So, if you look at that, at that small hill in the middle ground towards the right, you can see that it looks layered, but it's not that well layered. You know, that's sort of typical of what ancient rocks on Earth look like that are deposited in streams. But the rocks down at the bottom that look so throughgoing, that are much thinner in scale, those are the things that became candidates in our eyes for possible lake beds. So we just had to drive further to get down into that basin. And that's what we did. And then we got down to one of those thing layers. And so, here's what we found. And I've shown it graphically, here, to start off with. Where, we can see all the different layers. And so we sort of stack them all up on top of each other. And you can see the thickness there. We've got about 1 and a half meters of rock, and there's a very important geological contact. And the upper unit is called Gillespie, and the bottom unit is called Sheepbed and Sheepbed is what geologists call a mudstone. It is a rock that is literally made out of ancient mud. It is exactly the kind of thing we were hoping to find. The kind of deposit where once the flow in the river stops, the flow velocity drops below the threshold. And due to Stokes' Law for settling, the gravitational forces exceed the forces of the turbulence in the flow. And the particles now settle out of the water, down to the bottom and accumulate as mud. And then, the water circulates minerals that then converts it into a rock, and we get a mudstone. And then above that, we have contact with the rocks that were, the, the sediments, coarser grain, sandier, that were transported in the ancient streams. And so we know then that we've found a contact between the ancient river and the lake deposit. And then the rest of the stuff that you see here are features that form after the sediments come to rest in a term that geologist call diagenesis, which are all the geochemical things that happen during the conversion of sediment to rock. So, obviously what's involved here is fluid flowing through the pore space in the sediment. And precipitating minerals that make them hard. And one thing that I'll point out are these thing that we've called bumps, pits, and spires. They are features that, that look like that when you look at the rock, but there, it turns out that they're are things called concretions, which form by pointwise nucleation of minerals and then that propagates outwards in all directions to form a sphere. That then weathers out of the rock to form a kind of protuberance. And so, these concretions, we've seen these before on Mars. And, and we first discovered them at Meridiani. We called them blueberries because, before we had processed the color the spectral content was showing the blue up in the pictures that we had collected. But the important thing is, what's really remarkable about this is that we published a paper in late January of 2014. And in the same issue of Science the opportunity science team reported a second occurrence of concretions in a much older rock. At, at Meridiani Planum and now what is remarkable about this is that we have explored three very different terrains on Mars that all involve the activity of water and each of them has resulted in the formation of concretions. Now, I can tell you that if you get let out of a helicopter almost any place on Earth where you find sedimentary rocks that once formed in the presence of water, we usually don't find concretions. Concretions are cool and rock hounds collect them because they're actually rather uncommon. So the fact that we're three out of three on Mars is probably telling us something and we don't know what that means yet but it's an interesting trend that we've noticed. And then we've got veins and fractures that cross cut the rocks and they're filled with all kinds of hydrated minerals so. We see calcium sulfate filling these minerals and clay minerals as well which is one of the things that we were after. Okay. So here's what these rocks look like and these bumps and pits and spires you can see them there raised up creating little tiny shadows. And, and those are the concretions, those little bumps that spick, stick out of the rock. And then the rock is cross cut by these later fractures and this looks like something you'd see in a mining district. The rock's all fractured up. You know that fluids flu, flowed through the rock later, and so this is yet another phase of, of, of water, evidence of water that once flowed through the rock. But this time, instead of making clay, the water made sulfate minerals. But not the kind of sulfate minerals that form in acidic environments. We think the kind of sulfate minerals that formed in pH neutral environments. So the time came to drill and we did that. And on the right, you can see the hole that Curiosity drilled in 2013 and you can see the, the way that Opportunity ten years earlier. It has a tool called the rock abrasion tool, the RAT, and it grinds into the rock. And we get down a millimeter. It's enough to just take the veneer off the rock. But what you see going on there is, is something that, that geologists do in, in mineralogy lab called a streak test, where we take a, a white porcelain plate and you take a rock that you think might have iron oxide in it,. And if you scratch it across it, it makes a red streak. And so when we ground up this rock we created all this fine powder and we were amazed when it came back and it was red. Because from orbit we had seen the signature for hematite and even before we used the Mössbauer Spectrometer, just looking at the color all the geologists knew there was hematite in this rock and we had found what we were looking for. We kind of had the same experience when we drilled the hole and the Sheepbed mudstone with curiosity and the powder came out. The minute we saw this picture, we knew we had something very different from what we had found at Opportunity. Insto, instead of seeing the red color that's typical of the highly oxidized state of the planet today and all the iron is in the Fe+++ valence, what we see instead is a rock that has a grey color, which tells us if there is iron in there, it can't be all oxidized. And indeed, when we did get the mineralogy in there, we found out that iron was not present in hematite. It was present in magnetite which is a mixture of Fe++ and Fe+++. So that was good for us because we knew that we had not only found an ancient aquean, aqueous environment. It was, we also knew it was a lake. And we also knew that this was the kind of lake where there was reducing conditions, which really neat to see because that's important for planetary habitability. Okay, so, then we take the powder and we feed it into our instruments. And here is just a sample of the kind of data that we get. And this is data that comes from the quadrupole mass spectrometer. So they, we basically take the rock and we heat it up, as you can see here. It basically gets up to about 900, 950 degrees. It's Fahrenheit here because it's, I used this for general public. And we heat that rock up and what it does is it kicks out all of the volatiles and so the quadrupole mass spectrometer signal is on the y axis. And what you could see as we heat it up, the first thing that happens is we start to generate some water. And pretty much concurrent with the generation of water, we see CO2 go up. And we see that we're producing oxygen. And then oxygen kind of peaks out quickly and then drops out. Then carbon dioxide peaks after that and then begins to drop out. And then water is produced and then it begins to drop out but then the water comes back again. And, and where the line goes from water to the spectrum, you can see a, a smaller peak there that comes in. And that converts to about 850 degrees centigrade. And it turns out if you take clay minerals in the lab and you heat them up, the interware waters in the clay minerals will kick out at about 800 degrees centigrade. So that's the expression of, of the water coming off the rock from the clay minerals that we confirmed that were there with the x-ray diffraction unit that we had as well. The other cool thing that we see are two forms of sulfur. And we can see sulfur that is present in a molecule that has a, a mass of 64 and it turns out that that's sulfate. So there's calcium sulfate minerals in there, and, and that's the sulfate ion coming off. And then we have something that's at mass 34 and it turns out that's the sulfide ion that's coming off at that point. And that's important because sulfate is oxidized and sulfide is reduced. And so here we go again. We don't just have a lake, we have a lake that in the mud the conditions are reducing, and that's a very favorable kind of environment to potentially preserve evidence of organic compounds, which are reduced in their molecular structure. And on an oxidized planet, organics wouldn't stick around very long so we were happy to find these reduced rocks. Okay, so this is, you take all the data that we got and this is the kind of environment that we're talking about. And in previous Mars missions, you would've been shown examples from Earth of very extreme environments. Boiling pools, acid mine tailings with low pH, either really hot or really acidic, something really extreme. What this thing adds up to is something that's actually quite normal on Earth. It's probably the kind of a lake that comes and goes but we call a paleolake. But when the lake is present, it doesn't have to be very salty and it can be pH neutral. And so this a terrain down in Australia where there's a lot of rock around called the salt, which is typical for Mars. And if you weather it under normal conditions it produces neutral pH. And so where you dig a shovel full of the, of the mud out of there, you can recognize the clay minerals from the conversion of olivine, which weathers very easily in the presence of water to a kind of a, a clay mineral called saponite, which is an iron magnesium smectite clay. And, and so we imagine that if you had been around on Mars 3.8 billion years ago, you would've gotten the shovel out and found some very similar stuff, that we've got here. Now we'll change gears a little bit and, and talk about Mount Sharp because this is our ultimate destination. We've been driving since about the 4th of July 2013. And we hope to arrive there sometime toward the end of the summer 2014. And when we get there, we know that we're going to be encountering rocks this time that have been formed or altered in the presence of water. The layers that you see there are hundreds of meters thick and from orbit we see the signatures of hematite down low. Then the hematite gives way to layers that have clays in them and then those give way higher up to layers that have sulfates in them. And there, if you look, you kind of see that the lower foothills have buttes and mesas that are kind of smooth, but it gives way to a higher ridge that looks very jaggedy. It's a very rough looking rock. That turns out to be a very important stratigraphic contact. And when you look at the rocks that are above that from orbit, you don't see any of the spectral signatures for hydrated minerals. And so we believe that all those rocks, in fact, the great bulk of Mount Sharp may be composed of rocks that represent sediments accumulating, but not in the presence of water. Mars goes through this unidirectional transition from a planet that might've been earthlike and had water to something that looks very foreign today. On, on earth, the only analog are the driest desserts. And I like to call this the great desiccation event. And in terms of planetary significance, it, it's kind of like thinking about the great oxidation event on Earth where about 2.4 billion years ago there was a rise in the oxygen content of Earth. And had you been doing extrasolar planetology from a different solar system looking back at Earth, prior to 2.4 million years, billion years ago, you might not have seen any oxygen in the atmosphere. But, after 2.4, maybe you would have seen a spectral response from Earth's atmosphere that would've told you that it would've been oxidizing. In a similar way, at a grand planetary scale, maybe this is the same kind of thing. But instead of telling about the flowering of life on earth, it's telling about the demise of the aqueous environment on Mars. We would love to know what actually caused that and so if we go there and explore this, we've got a shot, at, at, at trying to collect some new data to help put a piece of the puzzle in there. So again, it sort of helps to make a reference to Earth. And, and remember, you know, when John Wesley Powell went down the Grand Canyon over a hundred years ago, they didn't know what these layers were. They didn't know what they what they meant. They didn't know what fossils might be preserved in them. They had really had no starting place, they only knew that the layers were there and that the layers are the archive of the history of the planet. So you look at the layers that are down at the bottom and they tell you about things that happened a long time ago and then you look at the layers that are above them and they tell you about things that also happened a long time ago, but a little bit younger than the things that were down at the bottom. And so all this happened hundreds of millions of years ago, but it's like reading a novel where each time you go up and look at a new layer maybe the planet has changed in some ways. So by looking at the series of layers you can sort of recreate a time series of the history of the planet. So that's what we're trying to do here. It's the same thing that we use to do, and still do, on Earth. So this gives you a sense of the scale of the Grand Canyon on the left there. And you can see that from top to bottom, everybody knows that the Grand Canyon is about a mile deep. Well, that's not even getting started with Gale. So the part of, of the mountain that we can potentially study there is equal to about half the depth of the Grand Canyon. And if we wanted to keep going all the way up and climb to the top of the mountain, which is about as high as Mount Whitney. We could go a lot further. Now, we don't think we're every going to drive Curiosity beyond the boundary where, you can see in the colors, it goes from green to pink. That's what I call this great desiccation event. That boundary represents, at Gale, when the planet went being, went from being wetter to potentially being terminally dry. All right, so we can put this into a global framework to give you a sense for why this is important. And here, you can see on the left we've got the Stratigraphy of Gale Crater. And down at the bottom, we've got some clays near the bottom. But mostly what we see in Mount Sharp at the bottom are sulfate minerals. That's what's in the yellow and red. And then we go up and, and we get a contact where there's a little bit of, of, of the mountain where we can't see too well. That's what's colored in gray. But then above that, we just see nothing but the spectral signature for dust up there. And so the, the vast majority of what's in Mount Sharp seems to be a time when it was just accumulating dust. In fact, we call these rocks dust stones. And we think that's what most of the mountain is made out of. Now if you go to the ancient terrains on Mars to places like Nili Fossae or Mawrth Vallis. These are rocks that from orbit have very strong signals of, for clay minerals that kind of places that Bethany Elman studies. And you see lots of iron and magnesium clays that are there. They look like they formed in the presence of of alteration of olivine and the presence of, of water. And so this what seems to be the time that the planet really wanted to make clays. Now, if you look up above Nili Fossae you go to Sinus Miriani which is where the Opportunity rover went to. And we know that all we ever had is clays there. But if Opportunity can drive about 100 kilometers, it would eventually get to a higher level where you would also see these dust stones that, that seem to post date the sulfates on Mars. And the point is that as you work your way around the planet, there's a general sense that the very early history of Mars is dominated by clays. The intermediate history of Mars is dominated by sulfates. And then as you go into the younger history of Mars, the planet dries out and then you get at least dust stones accumulating. So we were really interested to go to Gale because we only get one rover. It only goes to one place on the planet and, and if we live long enough, we, we could potentially get a taste of all these important, different eras in the history of Mars as it begins to dry out. It's a neat time to be a student and, and in planetary science. And, and the fun thing about working on Mars is that we're really beginning to get a toehold on understanding the, the evolution of its surface environment. The cool think about it is with these rovers, you can take these hypotheses and then go look at individual, small little things like rocks to make key measurements that allow you to test those, those hypotheses about planetary evolution.
