 I'm going to talk a little bit about the origins of grains. They're the sediment that gets transported and can eventually become sedimentary rocks. So we have three basic ways that we can get grains. One is the breaking up of prior rock for existing rock. And this process of breaking a rock into smaller grains is weathering. We have the way we can make grains chemically, which are the reactions of ions to form new minerals. So an example of that is the formation of clay minerals from the process of weathering or the formation of salts with the evaporation of water. Or the most abundant mineral that forms from ions is the formation of carbonate, which often forms as shells, but it can form from other processes. So speaking of shells, that gets us to the third type of grains, which are bits or pieces of biology. So these can be a variety of different compositions. We already mentioned shells. So we have the hard parts of biology. And those persist for a long time as the sediment is being transported. We also have pieces of organic matter. So this can be pieces of wood, branches, things, the bodies of organisms. For example, algae can create a lot of organic matter that gets buried and that eventually that organic matter eventually some of it decays and oxidizes, but some of it can provide the oil and gas that we use to run a lot of our economy. OK, so we can divide these types of grains into general classifications of where they come from and how they get there. So the breaking of rock, it starts with some pre-existing rock. And the grains are created where the rock is present. And they're almost always transported to get into sedimentary environments. So in this particular case, they are transported to an environment where they can eventually get deposited. The reaction of ions to form minerals can happen that way as well. So some of this happens in where the weathering is actually occurring, where you have chemical weathering. You can form clay minerals. But some of these form in place where they're actually preserved, like some of the salts and some of the carbonate minerals. Salt's usually transported very much, except maybe by wind, because they dissolve in water really easily. Carbonate minerals can be transported. So this is a mix of transported and forming in place where the sedimentary rocks are actually preserved. Again, the same is true for the biology. It can be transported as grains, but a lot of times the organisms can be preserved where they actually form. So for example, if you have trees on a floodplain, their roots can end up embedded and preserved in the floodplain deposits where they actually grew and formed. Coral reefs are an example of skeletons from the coral. Their bodies are actually forming the reefs themselves. And they're preserved again right where they form. An example of when they're transported is, for example, shells. So some of you in lab will be looking at grains that came from beaches. And there are bits of shells in that. And those shells get broken up through time and transported up and down the beach. So the bits of biology can, again, be transported or formed in place. Obviously, if grains are transported, they can tell you something about where those grains came from. So for example, if you're breaking up rock from the Sierra Nevada, which has intrusive igneous rocks, there are minerals called zircons in those. They can be transported down the rivers and eventually found by geologists and characterized. And they will retain a fingerprint of where they came from, of those granitic rocks in the Sierra Nevada mountains. If things form in place, the minerals forming in place from the ions in the water, they tell us something about the chemistry of that water. If you see salt crystals, you know that the water had a lot of ions in it. So if it's, for example, halite, esodium chloride, it has lots of sodium and chlorine, where it did have. And the biology is particularly good when it's in place about telling us what the ecology was, which organisms were living there. And that can give us very, very useful information about the environment. And we can use a relationship between the bits of biology, the bits of organisms, and the depositional environment to reconstruct how those organisms grew and where they grew. Thanks for watching.