We're going to delve a little bit deeper into geologic thinking with this mini-lecture. Geologists reason differently from other scientists, and we do so because of the vastness of geologic time. We have to deal with time frames of millions, even billions of years, because experiments over those kinds of time frames are very hard to run, because data are missing. You might have a sequence of rocks that has 2, 3, 400 million years of...
the geologic record missing in the middle of it. Because storytelling is part of geologic understanding. We build the history of a place by telling the story of it.
And because many concepts that deal with geologic principles and processes aren't linear, you can't lay them out in a line, step one, step two, step three, step four, because there are loops that come around and affect each other. And so that That makes it important for geologists to think in more complex ways. Let's just start with interpretation.
When a geologist walks up to an outcrop like this, the first thing they do is start to think about what's important to look at, what's important to ignore, and what the geologic story of this particular region might be. As it happens, this is... the most famous unconformity in the world.
It's a place called Sickor Point in Scotland, and it's where James Hutton first started to think about geologic time. So what would a geologist look at here? Well, starting with observations, what do you see?
Perhaps the first thing you see is rocks that are in layers that are nearly vertical. And then maybe you also see a second set of rocks that are in layers that are not... Not quite horizontal, but much closer to horizontal. And if you looked very carefully here and other places up and down the coast, you might notice that these vertical rocks, the blue lines, are always underneath these nearly horizontal rocks, the green lines. So they must have formed first, and the rock on top, the sandstone, must have formed later.
Now that's a very fundamental first step. At this point you might step a little bit closer and look carefully at what these rocks are made of. You can't do that in this picture, so I'll give you some ideas. This rock in the foreground that's forming the vertical layers is made of mud. It's a mudstone.
It's very fine-grained black rock. Now you have seen mud before, right? Does mud form in layers when it piles up?
Does it form in layers that are vertical like that? No, of course not. It forms in layers that are horizontal or close to it.
So now we're thinking like a geologist. Now we have a mud rock where the layer is nearly vertical. So how could that have happened? Well, first you'd have to lay the mud down in a horizontal layer.
Then you'd have to pile up stuff on top of it and turn it into a rock. Then you would have to tilt it up and make it vertical. Make sense? But we're not done. Because there's another rock on top of it, and that's not horizontal either.
It's made of sand, by the way, that red rock, red sandstone. And so you've seen sand pile up. Sand piles up horizontal too, doesn't it? So now you have this vertical hard rock layering underneath, and you're sitting there on a beach, or in a near-coastal environment, or maybe at the edge of a river. and you're piling up sand in horizontal layers.
And then you have to bury that and turn it into a rock and tilt it and bring it back up again. All of that's going to take a really long time, right? Well, and that's exactly what Hutton thought when he first stood here and looked at it and decided that geologic time must be very, very long.
So geologic thinking is interpretive. It's also historical. The goal in this picture is not to get down to this particular outcrop and figure out what's going on there, but to give you an idea of how geologists build up a story of a rock, how we put it into a narrative context and build the time into our interpretation of what is happening.
So we look at the oldest stuff first, that's always at the bottom, and we see that in this particular place there are ocean sediments. in the lowest rocks we see. So that's the first thing. They were deposited in an ocean. And then they were compressed and turned into mountains.
That sediment was turned into mountains. Then there were some volcanoes and a little basin formed, that little pink basin. And then a long period of deposition and another big basin, a lot of sediment forming up in that nice yellow basin.
And then nothing for a long time. We're missing, missing time from 65 million years ago to maybe five or six million years ago. There aren't any rocks at all. So something happened. It all got washed away.
But we don't know what it was. We have a hole in our story. And finally, we have some very young volcanoes and some more basins forming. That's an interpretation of a particular place.
That's how geologists look at the history of a particular region. Now, philosophers have studied geoscientists and paid attention to how they think and come up with the idea that geologists use a unique skill set in interpreting rocks and in learning about the Earth. And the philosophers came up with...
four unique skills that geoscientists use that other scientists don't use nearly as much. The first one is taking a long view of time. The second one is using a systems-based approach to interpretation. The third one is translating field observations into data. And the fourth one is being able to visualize three-dimensional things in two dimensions.
And we're going to look at each one of those. By the way, this is a picture of the Dolomite Mountains in Italy. So let's start with time.
Geologists understand that the Earth is very old and that processes take a very long time. When you start to think about geologic time, it alters your perception of humans'place in the world. For example, if you start to think about a volcanic eruption, not in terms of the immediate hazard to humans, but rather as a step in producing a mountain range that's been built up over thousands or maybe even millions of years, then you're starting to think like a geoscientist.
Geologists define a couple of kinds of events that happen regularly in Earth history. The one category we call low frequency high impact events, things like asteroid impacts or ice ages or massive floods or large volcanic eruptions. These things can change the landscape and they can change the climate.
They can have a very large impact on Earth, but they happen very quickly and they're over very quickly. In addition to that, there is the background slow and constant change. For example, mountains being pushed higher and higher by tectonic processes and erosion slowly wearing away those mountains. Those ordinary, everyday, slow change is responsible for most of the vision of Earth as we see it today.
And understanding that slow change is an important part of geology. So this ability to see Earth processes over the long time and read the rock record and interpret how Earth was shaped allows geologists to bring insight to really important questions like climate change. We can actually look at climate indicators in really old rocks and start to help other scientists in collaboration answer questions about what the world might look like moving forward. The third special thinking skill is the understanding of complexities.
This is really paying attention to how processes interact, and one of the important key complexities that form and shape the Earth are called feedback loops. So let's take a look at a feedback loop. A feedback loop has been described as a threshold learning concept, and by that I mean it's something where before you understand it, you see the world one way, And after you understand it, you see the world completely differently.
And there's no way to go back to your prior way of thinking. Your way of thinking has been transformed by understanding how feedback loops work. So how does a feedback loop work?
Well, a feedback loop is essentially the idea that when you start to make a change, that change will impact something else, which impacts something else, which impacts something else, and circles back. to your initial position. And then the question becomes, when it circles back, does it amplify the original change or does it dampen it?
Does it bring it back towards equilibrium? This sketch shows a positive feedback loop. It starts with an initial change of a little bit of cooling. That increases the amount of snow and ice, which reflects sunlight, so less solar radiation is absorbed.
So there's more cooling, which makes more snow and ice, which absorbs less sunlight, which causes more cooling. So you can see that the initial change started you out in a loop that led back to pushing the system in the same direction, a positive feedback loop. The next important geologic skill is learning in the field.
Observations play a central role in geologic studies. And it is important for professionals to be able to see what's important, but also communicate that to other geoscientists. So the ability to translate the observations that you see into the field into some sort of inscription that other geoscientists can read is vital to the profession. That means being able to understand the symbols that geologists use on maps and on drawings and be able to read those when you see them from someone else's work, but also produce them from your own.
You'll get some experience with this. Let's start out by looking at an example of an outcrop. What do you think a geologist looks at in this outcrop?
What's going to be important for them to communicate to other geoscientists? One thing would be... that these rocks are tilted.
And so that's going to be somehow inscribed onto a map that a geologist would make of this area. Another thing they're going to want to note is that these rocks are in fact folded. And you can see that they're tilted in the opposite direction on the other side.
So the location of that fold is important, and the size of it, and the scope of it. Another thing geologists would make note of here are the kinds of rocks that form up these layers. so they can go back and interpret what the geologic history of this region is.
All of that can be translated into symbols and words that other geologists could use to understand this area and to envision when they step up to a map and look at it to make a picture in their mind of a fold. And that brings us to the last geologic skill, and that is... spatial thinking. Spatial thinking in geosciences falls into a couple of categories.
The vast expanse, the long wide areas that are connected to each other, standing at the Grand Canyon and looking across to the other side and realizing that those layers were once connected, for example, is expansive thinking. X-ray eyes, being able to see what's happening below the surface. You look at a rock at the surface and you can envision what must be going on below the surface. Three-dimensional thinking, being able to look at someone else's map, like the side along hill we just looked at in the last picture, and envision the three-dimensional picture of what it must look like. And vice versa, being able to visualize something in three dimensions and put it down in two dimensions so others can read it.
All of these spatial thinking skills require some natural ability and some learned ability and some specialized tools. And you'll get an opportunity to work with all of these things this semester. Do you recognize the art?
That's by an artist named M.C. Escher who lived from 1898 to 1972 and was extraordinary at spatial thinking. Let's give spatial thinking a try.
Here is a sketch of a river. You can tell that it's flowing towards you out of the page. And three cross sections drawn along lines 1, 2, and 3. Now, A is pretty easy. We've already cut the box across the front and produced a cross section that looks very much like A. So A is the cross section you'd get if you sliced this river at line number 2 and looked at it end on.
What about B? What about C? Which direction of the slice is going to give you a cross section that looks like B? or like C.
You can do that, right? That's facial thinking.