Practical Geology

Reading rock samples like the pages of a book, Professor Cotter recounts the stories they tell of change across vast stretches of time. He presents three key concepts that will open your mind to the fun and fascination of practical geology. Then he focuses on the idea of deep time, noting that humans have been around for only an infinitesimal fraction of Earth’s 4.6-billion-year geologic drama.

Geomorphology is the study of landscapes and their individual landforms. Learn the five major influences on landscape formation. Use this background to tour the US, which is a remarkable laboratory of geomorphology with features such as the Appalachian and Rocky Mountains, the Grand Canyon and Channeled Scablands, the Great Plains and Precambrian shield, the Coastal Plain and Florida, and more.

Go outside and find an outcrop—a roadcut, cliff face, or other site where rocks are exposed. These are ideal places for practicing field geology. Professor Cotter gives tips on safety, maps, tools, and techniques. A notebook and careful record-keeping are essential. Amateur geologists can make important discoveries, so field geology is your chance to advance knowledge while enjoying the outdoors.

Rivers are the key to understanding why many landscapes look the way they do. Study how rivers form, how they sculpt the land, how water and sediment move in a river, and how rivers change course over time. Rivers also create habitats for plants and animals, both of which influence the landscape. Finally, signs of vanished rivers tell the story of geologic events in the deep past.

Visit the beach with a geologist’s eyes and see how the interaction of waves, ocean currents, and winds lead to the ebb and flow of sediments and blending of landforms. Consider the four types of waves and what they reveal about the ocean floor just offshore. Also, zero in on individual grains of sand, identifying their minerals and tracing their origin. Reflect on why beaches are sandy at all.

Sedimentary rocks—those formed from sediment deposited by water or wind—make up a substantial majority of rocks at Earth’s surface. In this lecture, focus on clastic rocks, which are composed of broken fragments of pre-existing rocks. The fragments can vary in size from clay particles to silt, sand, gravel, and larger pieces. Learn how these rocks form and the rich stories they tell about the past.

Steppes and deserts make up almost a third of Earth’s land surface and are an ideal place to practice geology due to the distinctive landforms, often unobstructed by vegetation. Explore alluvial fans, washes, playa lakes, dunes, and other features typical of arid regions. Also ask why steppes and deserts are so dry. What combination of surface, ocean, and atmospheric conditions produce them?

Investigate glaciers, which now cover about 10% of Earth’s land area; 25,000 years ago, they covered 30%. Learn how to spot evidence of past glaciation—from sculpted valleys in Yosemite National Park, to the cliffs at Vicksburg, Mississippi (which formed far from glaciers), to Minnesota’s 10,000 lakes. Dig into the physics of glaciers: how they develop and the forces they exert.

Check out limestone, one of nature’s most amazing rocks, with medical, economic, and sightseeing benefits. Not to mention, limestone provides insight into environments eons ago. Examine its chemistry and the ways it forms. Survey different kinds of limestone, including types that preserve detailed fossils. Finally, look at sinkholes and caves, which occur in limestone karst topography.

Starting with the concept of strata—parallel layers of sedimentary rock lying one atop the other—learn how to look at a cliff face and read the strata like an epic adventure. The story can encompass hundreds of millions of years, involving advancing and retreating glaciers, falling and rising seas, the ebb and flow of life, and much else. Work up to the paragon of stratigraphy, the Grand Canyon.

Fossils are one of the most exciting components of field geology. The term covers not only preserved ancient life-forms, but also evidence of their activity, such as footprints. Look at different ways nature has of preserving fossils—by encasing in amber, freezing, pickling, chemical alteration, and other natural processes. Ask what life-forms are likely to be fossilized and in what environments.

Having learned about sediments, sedimentary environments, and how fossils are preserved, you are ready to go fossil hunting! Professor Cotter prepares you with background on rules and regulations, strategies for finding the best sites, and how to photograph and collect specimens. He closes with a quiz, challenging you to predict the types of fossils associated with different geologic formations.

Soil may be the most important geologic resource on the planet. Discover how geologists classify soils, focusing on the concept of soil horizons, which are distinct layers that often vary in composition, color, and texture. Analyze how this cross section, which signals soil fertility, differs depending on the type of biome. Learn how soils form and how easily they are destroyed by erosion.

Dig into the mystery of groundwater. Apart from sinkholes and caves, there are no underground lakes or rivers. Instead, water fills the voids in porous rocks below a certain depth, called the water table. Discover how wells are dug and why it’s a waste of money to hire a dowser, since water is practically everywhere if you dig deep enough. Also, consider the problem of groundwater pollution.

Stressing that he is not a medical doctor, Professor Cotter delves into the healthful and harmful effects of geologically sourced substances. Some have proven benefits, such as the antibacterial properties of salt and copper. Others can be deadly. For example, radon, a gaseous product of radioactive decay, causes lung cancer. Asbestos, a fibrous silicate mineral, is similarly dangerous to breathe.

Learn what it’s like to walk on barely cooled lava from an active volcano—one of many fascinating geologic experiences you can have in volcanic landscapes. Examine the different types of volcanoes and volcanic rocks, and which active sites are safe to explore and which you should avoid. In field geology you should be prepared, so review the special precautions to take when visiting volcanoes.

Rocks are made up of minerals, which give rocks their immense variety. For example, the mineral quartz has the crystalline clarity of ice, while graphite is opaque and slippery, and pyrite has a metallic sheen. Most rocks are a mix of different minerals. Survey the most common types, analyze their chemistry and molecular structure, and learn how to identify them through a series of simple tests.

Having studied igneous rocks that cool quickly in Lecture 16, which dealt with volcanoes, now turn to igneous rocks that cool deep underground over the course of millions of years. Find out how to distinguish granite from diorite, gabbro, and other intrusive igneous rocks. Learn about notable batholiths, such as Yosemite’s Half Dome, and look at the abundant uses for granite and similar rocks.

Metamorphic rocks form under conditions halfway between those of sedimentary and igneous rocks. A good analogy is the process of glacier formation that turns snow into dense, interlocking crystals of ice. Focus on foliated metamorphic rocks, such as slate and gneiss, which have lineation patterns. Geologists can read these patterns to reconstruct ancient mountain ranges and plate boundaries.

Turn to non-foliated metamorphic rocks, those without a distinctive mineral orientation. Investigate the different geologic conditions that create such rocks. Then survey a wide selection, spotlighting their beauty (marble), utility (soapstone), durability (quartzite), and economic value (banded iron formations)—some have all four! Professor Cotter discusses a few of his favorite metamorphic sites.

The most highly prized rocks among non-geologists are gemstones. This lecture covers all 12 birthstones, plus other gems, probing the shifting categories of precious and semi-precious gems. You learn how gems form and where to find them. Even more difficult to find are meteorites. Hear tips for identifying these extraterrestrial rocks, which are unlike anything native to Earth.

Mining is one of the oldest and most important applications of practical geology. Find out how metals are classified and how most are associated with igneous and metamorphic deposits. Some metals, like gold, can be mined in a pure—"native”—state that requires little processing. Discover how and where to go prospecting for gold, using the panning process perfected by the Forty-Niners in California.

Trace the history of oil exploration and recovery, focusing on the geology of petroleum and natural gas formations. To strike oil, you need to find a source rock, a reservoir rock, a caprock, and a structural feature called a trap where oil can pool. Survey some of the world’s most productive oil fields, and investigate the plusses and minuses of hydraulic fracturing, also known as “fracking.”

Consider how to put your knowledge of geology to use. Issues faced by your community may benefit from geologic insights about groundwater, watersheds, roadways, pollution, and historic questions such as abandoned mines and quarries. Practical geology will only grow in importance as the world deals with climate change, resource shortages, and the pressing need to live in harmony with the planet.