In the beginning, there was no need for geology because there were no rocks, minerals, or Earth. This lecture takes a;big picture look at the formation and early evolution of the universe.
The planets formed from a disc of cosmic dust rotating around the Sun. The composition of the planets varies. Those nearest the Sun are made of rock, while those most distant are made of gases.
Until the 20th century, geologists believed that the size, shape, and location of the continents had been fixed in their present configuration for billions of years. Then the theory of plate tectonics changed everything.
This lecture describes plate tectonics; the rifting of continents and spreading of the sea floor; the force that drives this process; and the cyclic creation, breaking up, and reformation of supercontinents.
A full understanding of Earth's origin, the evolution of its surface, and how processes shape the land requires knowledge of minerals, how they form, and their basic classification.
Minerals are classified by their dominant, negatively charged grouping (anion). By far, the major rock-forming minerals are silicates built around the silicate anion. All other minerals are classified as non-silicates.
For the average geologist in the field, mineral identification is made based on a series of physical properties. Color streak, cleavage, acid reaction, and hardness are four such tests.
Of the three types of rock; igneous, sedimentary, and metamorphic; igneous rocks constitute 80 percent of Earth's crust. They are classified and named based on their texture and mineral composition.
Sedimentary rocks form from the products of weathering and cover 75 percent of Earth's land surface. As a result, they are the type of rock that is normally seen exposed at Earth's surface.
A metamorphic rock is any rock that forms from a previously existing rock as the result of heat, pressure, and chemically active fluids. This process takes place only at great depth.
This lecture introduces volcanism, which is associated with three types of sites: convergent plate margins, divergent plate margins, and hot spots. The composition of magma is crucial in determining the intensity of an eruption.
The site of an eruption and the type of magma involved govern whether the resulting volcano will be a cinder cone, a shield volcano, or a strato- or composite volcano. Eruptions are further classified based on severity.
The Hawaiian Islands resulted from the movement of the Pacific plate over a volcanic hot spot. Yellowstone Park also sits over a hot spot that caused violent eruptions in prehistory. Another such eruption is likely.
Although mass wasting is one of the most important processes responsible for the evolution of the landscape, most people are unaware of its existence. The driving force of mass wasting is gravity.
This lecture describes how mass wasting works and where to observe it. Although flows, slides, and falls account for the most dramatic forms of mass wasting, by far the greatest change is achieved by creep.
Weathering is any process whereby rocks either disintegrate or decompose. The primary agent of physical weathering is the freezing and thawing of water, known as frost wedging.
This lecture explores why soils are so critical to sustaining plant life. Clay minerals turn out to be the key component. Different climates have characteristic soil types, some of which are ideal for agriculture.
Soil is the end product of a complex series of factors, the most important of which is climate. The type of soil that forms is controlled by the combination of annual precipitation and temperature.
Despite holding only a tiny fraction of the world's fresh water, streams are the major agent of erosion wherever water can exist, including the desert. Streams are either interior (terminating inland) or exterior (ending in the ocean).
Surprisingly, there is no scientific consensus on the process of landscape evolution. One prominent theory, proposed by William Davis, sees land evolving through three stages of maturity due to stream erosion.
With minor modifications, Davis's theory on the three stages of a stream's life holds true for arid regions as well as humid regions. Nevada is typical of the process of stream erosion in arid regions.
Glaciers are second only to streams as an agent of erosion. In areas such as the Alps and Canadian Rockies, the combined effects of stream and glacial erosion have carved some of the most spectacular scenery on the planet.
Earth's largest readily available source of fresh water is groundwater. This lecture looks at the types of rock most suitable for storing groundwater. Those that produce water most easily are classified as aquifers.
Overproduction of an aquifer usually results in the lowering of the water table. Groundwater is not a renewable resource. It may take hundreds of thousands of years to replace a gallon of groundwater with a new gallon.
One of the most spectacular results of groundwater in action is karst topography; irregular topography created by the surface and groundwater dissolution of underlying soluble rock, usually limestone.
Nearly every human activity, from fertilizing yards to parking cars, has the potential to contaminate groundwater. Poorly designed and built landfills rank high among potential contaminants.
Deformation is any process in which rock changes in size and/or shape. The three types of deformation are elastic, plastic, and brittle, corresponding to rocks that bounce back, bend, and break.
Rock structures form as a result of the application of stress beyond the strength of the rock. The three basic rock structures are folds, faults, and joints. This lecture focuses on folds, which are caused by compression.
Faults and joints comprise the two types of brittle deformation. Rocks move along faults. There is little or no movement along joints. One well-known fault is the San Andreas, a strike-slip fault.
Earthquakes occur in the same regions as the most violent volcanoes. Both result from the activity of convergent plate or divergent plate margins. Convergent plate margins produce the most violent of both events.
The intensity of an earthquake refers to the observed results of the quaking and the amount of damage. An earthquake's magnitude measures the amount of Earth movement. Tsunamis are an earthquake-generated phenomenon.
Earthquakes have been detected for centuries with simple devices, but the ability to study the full impact of earthquakes awaited the invention of a seismograph that could not only detect but actually measure Earth movement.
Mountains are of four types: volcanic, domal, block-fault, and foldbelt. The most impressive are foldbelt mountains such as the Himalayas, which are created by colliding plates at zones of subduction.
Orogeny refers to the processes that create foldbelt mountains. These form under three scenarios: ocean-continent collisions, ocean-island arc-continent collisions, and continent-continent collisions.
Coal comes from wood that has been preserved in environments where oxygen and microbial activity is low. Coal is ranked by its carbon content, which varies widely in the abundant deposits in the United States.
Petroleum is formed when marine material is buried in porous rock capped by an impermeable layer. Predictions about the inevitable decrease and disappearance of oil resources appear to be all too accurate.