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Geosciences LibreTexts

1: Introduction and Geology

  • Page ID
    • 1.1: The Earth- The Ground Beneath Your Feet
      We will be dealing almost exclusively with the Earth’s continental surfaces. There are profound geological differences between the continents and the ocean basins, in terms of origin, age, history, and composition. Here I’ll present, very briefly, some basic things about geology.
    • 1.2: Minerals
      The technical definition of a mineral is elegant: a naturally occurring crystalline solid. That definition calls for a bit of commentary, though.
    • 1.3: Rocks
      Rocks, in the form of what is called bedrock, are exposed at the Earth’s surface over wide areas, and they everywhere underlie the unconsolidated surficial 79 materials, called regolith, you will learn about later in this chapter.
    • 1.4: Bedrock
      By bedrock I mean solid rock, exposed at the Earth’s surface or buried at shallow depths. A great many geologists spend most of their professional lives studying the bedrock of the Earth’s continents.
    • 1.5: Weathering
      Weathering is the term used for the chemical decomposition and physical disintegration of bedrock at and just below the earth’s surface.
    • 1.6: The Mineral Particles of the Earth's Surface Materials
      It seems a good idea, at this point, to describe the most common kinds of mineral particles in the ground under your feet—the materials that in the sections to follow are called regolith, sediment, and soil (regolith being the most inclusive term, as you will see).
    • 1.7: Regolith
      The term regolith is used for the layer or mantle of fragmental and unconsolidated rock and mineral material, whether residual or transported, that rests on bedrock. One might quibble that the definition excludes fragmental material that happens to be locally cemented by surficial processes butis otherwise closely related to nearby unconsolidated material.
    • 1.8: Sediment
      When regolith is mobilized or entrained, by flowing water, or by the wind, or by moving glacier ice, it is called sediment, because, as the term implies (the Latin verb sedere means to sit), it eventually comes to rest again as a deposit. Here I will touch upon only a few aspects of sediments. You will hear much more about sediment movement, and sediment deposits, in later chapters, especially the chapters on rivers, on glaciers, and on coasts.
    • 1.9: Soils
      Along with oxygen and water, soils are essential to human existence. Almost all of our food comes, directly or indirectly, from crops grown in the soil.
    • 1.10: Latitude and Longitude
      You probably know already that the basic coordinate system that’s used to describe the position of a point on the Earth's surface is latitude and longitude.
    • 1.11: Maps
      Earth science is a very map-oriented discipline, because geologists are always having to view and think about the disposition of rock bodies across the landscape. This section provides just a little elementary material about maps.
    • 1.12: Topographic Maps
      Almost all of the area of the United States has been represented on topographic maps at various scales.
    • 1.13: Stream Networks, Drainage Basins, and Divides
      In most areas of the world, except in the driest of deserts (and beneath glaciers), one can trace fairly easily on a topographic map the system of main streams and their tributaries. In some places streams “expand” into lakes, but the principle is the same.
    • 1.14: Geologic Maps and Cross Sections
      Field geologists who study and map the bedrock that underlies an area of the land surface attempt to recognize rock units, which they can then represent on geologic maps. Rock types are not randomly arranged in the Earth’s crust but tend to exist in distinctive bodies called rock units.

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