Geology 101 Midterm

Erosion

Processes by which rock, sand, and soil are broken down and carried away (i.e. weathering, glaciation).

Streak

The color of a mineral's powder.

Continental Rift

The region on a continent where new crust is being created, and the plates on either side of the rift are moving apart.

Map Scale

The relationship between the size of an object on a map and the size of the actual feature on Earth's surface.

Asthenosphere

The soft layer of the mantle on which the lithosphere floats.

Crust

The thin and solid outermost layer of the Earth above the mantle.

Luster

The way a mineral reflects light from its surface.

Clay

the finest soil, made up of particles that are less than 0.002 mm in diameter.

Cleavage

A mineral's ability to split easily along flat surfaces.

Physical weathering

Any process that breaks rock down into smaller pieces without changing the chemistry of the rock; typically wind and water.

Interpreting Physiographic Maps

A physiographic map shows the physical features of a landscape, such as mountains, plains, plateaus, and basins. These maps are useful for understanding the broad-scale geography of a region and how it relates to other regions.

Creating a Topographic Profile

1. Choose the area for which you want to create a profile. This could be a hill, a mountain, a river, or any other landform. 2. Collect data about the elevation of the land along the path where you want to create the profile. You can use a topographic map, a GPS device, or other tools to collect this data. 3. Draw a straight line on the map or the terrain where you want to create the profile. This line should represent the path along which you want to create the profile. 4. Mark the points where the line intersects with contour lines on the map or the terrain. Contour lines represent the elevation of the land at different intervals, usually in feet or meters. The closer the contour lines are to each other, the steeper the terrain. 5. Record the elevation at each point where the line intersects with the contour lines. 6. Plot the elevations on a graph, with the distance along the line on the x-axis and the elevation on the y-axis. 7. Connect the dots to create a continuous line that represents the topographic profile of the land along the path you chose. 8. Add any additional information or labels to the graph as needed. 9. Interpret the profile to understand the terrain features and their characteristics, such as steepness, slope, and changes in elevation.

Using the PLSS

1. Determine the location of the land: The first step is to identify the location of the land you are interested in using maps or GPS coordinates. 2. Identify the Township and Range: Once you have the location, use the Township and Range system to identify the specific area of the land. A township is a square unit of land that is six miles on each side, and a range is a column of townships running north and south. 3. Determine the Section: Each township is divided into 36 sections, which are numbered from 1 to 36. To determine which section the land is located in, count from the northeast corner of the township. 4. Understand the legal description: The legal description of the land will include the township, range, and section numbers, as well as other information, such as the meridian and the baseline. The legal description is used to identify the land in legal documents. 5. Verify the information: Verify the information with local government offices, such as the county surveyor's office or the Bureau of Land Management.

Understanding the Characteristics of a Mineral

1. It must be naturally occurring: Minerals are formed through geological processes, and they are not made by humans or other living organisms. 2. It must be inorganic: Minerals do not contain organic compounds, such as proteins, fats, or carbohydrates. 3. It must have a crystalline structure: Minerals have a regular arrangement of atoms that form a crystal lattice, which gives them a distinct shape and internal structure. 4. It must have a definite chemical composition: Minerals have a fixed chemical formula that specifies the types and proportions of atoms that make up the mineral. 5. It must be solid: Minerals are solid substances at normal temperatures and pressures.

Understanding the Difference Between Chemical and Physical Weathering

1. Physical weathering is the process by which rocks and other materials are broken down into smaller pieces without any change in their chemical composition. This type of weathering is often caused by physical forces such as water, wind, or ice. For example, water can freeze in cracks in rocks and cause the rock to break apart. Similarly, wind can carry sand and other particles that can erode and abrade the surface of rocks over time. 2. Chemical weathering, on the other hand, is the process by which rocks and other materials are broken down through chemical reactions. This type of weathering is often caused by exposure to water and other chemicals, such as acids. For example, rainwater that is slightly acidic can react with certain minerals in rocks, causing them to dissolve or change their chemical composition.

Understanding How Minerals Form

1. The most common way that minerals form is through crystallization from a molten state. This happens when magma, which is molten rock, cools and solidifies. As the magma cools, the atoms and molecules that make up the magma begin to arrange themselves in a repeating pattern, forming crystals. The type of mineral that forms depends on the chemical composition of the magma. 2. Another way that minerals form is through precipitation from a solution. This happens when dissolved minerals in water become concentrated enough to form crystals. For example, when seawater evaporates, the salts in the water become more concentrated, eventually forming crystals of minerals such as halite (table salt) and gypsum. 3. Minerals can also form through metamorphism, which is the process of changing the physical and chemical properties of a rock through heat and pressure. During metamorphism, minerals in a rock can be altered or replaced with new minerals. 4. Finally, some minerals are formed through biological processes, such as the formation of shells and skeletons by marine organisms. For example, calcite, which is a common mineral found in limestone, is formed from the shells of marine animals.

Absolute Age Dating

A Method that enables scientists to determine the actual age of certain rocks and other objects.

Fault

A crack in the earth's crust resulting from the displacement of one side with respect to the other.

Cross section

A diagram representing the geologic features intersecting a vertical plane, and is used to illustrate an area's structure and stratigraphy that would otherwise be hidden underground. The features described in a cross section can include rock units, faults, topography, and more.

Alluvial Fan

A fan-shaped deposit of sediment formed when a stream's slope is abruptly reduced.

Body fossil

A fossil that consists of the preserved body of an animal or plant or an imprint of the body.

Drainage Divide

A geographical barrier, such as a ridge, hill, or mountain, separating one watershed land area from another.

Interpreting Geologic Maps

A geologic map shows the distribution and types of rocks and geologic formations on the earth's surface. Different colors and patterns are used to represent different rock types, ages, and structures. By analyzing a geologic map, you can understand the geologic history and processes that have shaped the landscape over time.

Chert

A hard, compact, fine-grained sedimentary rock formed almost entirely of silica.

Contour line

A line on a topographic map that connects points of equal elevation.

Delta

A low triangular area where a river divides before entering a larger body of water.

Topographic Map

A map that shows the surface features of an area.

Hardness

A measure of how easily a mineral can be scratched.

Interpreting Raised Relief Maps

A raised relief map is a three-dimensional representation of a landscape, where the elevations and contours are exaggerated to show the relief of the land. These maps are useful for visualizing terrain features, such as mountains, valleys, and canyons, in a more realistic way than traditional topographic maps.

Gradient

A rate of inclination; a slope.

Radioactive Decay

A spontaneous process in which unstable nuclei lose energy by emitting radiation.

Braided Stream

A stream or river that is composed of multiple channels that divide and rejoin around sediment bars.

Island Arc

A string of volcanoes that form as the result of subduction of one oceanic plate beneath a second oceanic plate.

Interpreting Tectonic Maps

A tectonic map shows the boundaries of tectonic plates and their movements. These maps are used to study the interactions between the plates and the resulting geologic features, such as mountains, volcanoes, and earthquakes.

Convergent Plate Boundary

A tectonic plate boundary where two plates collide, come together, or crash into each other.

Interpreting Topographic Maps

A topographic map shows the elevation and shape of the earth's surface, including the location of natural and human-made features. These maps use contour lines to represent changes in elevation and can help you understand the geography of an area, such as the slope of the land, the location of rivers and lakes, and the types of vegetation present.

Trace fossil

A type of fossil that provides evidence of the activities of ancient organisms.

Nonconformity

A type of unconformity in which layered sedimentary rocks lie on an erosion surface cut into igneous or metamorphic rocks.

Disconformity

A type of unconformity in which the sedimentary layers above and below the unconformity are parallel.

Relative Age Dating

A way to describe the age of one object or event compared to another object or event.

Hotspot

A weak spot in the middle of a tectonic plate where magma surfaces; forms a volcano (ex: Hawaii & Yellowstone).

Bentonite

An aluminosilicate clay that swells in water and has powerful properties of adsorption.

Discharge

An outflow of water from a stream, pipe, groundwater aquifer, or watershed; the opposite of recharge.

Unconformities

An unconformity is a gap in the geological record that occurs when sedimentation is interrupted, erosion occurs, and then sedimentation resumes. Unconformities represent periods of time when no deposition or erosion occurred, and are indicated by a change in the rock type or by a physical break in the rock sequence.

Isotope

Atoms of the same element that have different numbers of neutrons.

Divergent Plate Boundary

Boundary between tectonic plates in which the two plates move away from each other, and new crust is created between them.

Transform Plate Boundary

Boundary between two plates that are sliding past each other.

Understanding Carbonate Rocks

Carbonate rocks are made up primarily of the mineral calcite (CaCO3), which is formed from the shells of marine organisms such as coral and mollusks. These rocks can also include other minerals like dolomite, which is formed from the alteration of limestone. Examples of carbonate rocks include limestone and dolostone.

Understanding Chemical Rocks

Chemical rocks are formed from the precipitation of minerals from water, often in shallow seas or lakes. This can occur when the water becomes saturated with minerals, causing them to precipitate out and form layers over time. Examples of chemical rocks include evaporites (such as halite or rock salt) and chert (a type of silica rock).

Flute

Grooves carved out by the forces of fluid flow and sediment loads.

Understanding Continental Shelf/Deep Sea Environments

Continental shelf and deep-sea environments: These environments are found beyond the continental shelf and include submarine canyons, abyssal plains, and seamounts. Sedimentary rocks formed in these environments are typically composed of fine-grained sediment, such as clay and silt, and can contain microfossils and volcanic ash.

Where can Plate Boundaries be found?

Currently, divergent boundaries can be found at the Mid-Atlantic Ridge, the East African Rift Zone, and the Red Sea Rift. Transform boundaries can be found along the San Andreas Fault, the Alpine Fault in New Zealand, and the North Anatolian Fault in Turkey. Convergent boundaries can be found along the Pacific Ring of Fire, including the Andes Mountains, the Himalayas, and the Aleutian Islands.

Strata

Layers of sedimentary rock.

Flood Plain

Flat land near the edges of rivers formed by mud and silt deposited by floods.

Understanding Grain Sizes

Grain size refers to the diameter of the particles that make up sediment. The standard classifications for grain size are gravel, sand, silt, and clay. Gravel particles have a diameter greater than 2 millimeters, while sand particles have a diameter between 0.0625 and 2 millimeters. Silt particles have a diameter between 0.0039 and 0.0625 millimeters, and clay particles have a diameter less than 0.0039 millimeters.

Latitude and Longitude

Latitude is a horizontal line that represents North and South of the equator. Longitude is a vertical line that represents East and West of the prime meridian.

Understanding Marine Environments

Marine environments: Marine environments include oceans, seas, and estuaries. Sedimentary rocks formed in marine environments are typically composed of fossil shells, carbonate minerals, and fine-grained sediment such as clay and silt. These rocks are often characterized by ripple marks, cross bedding, and other sedimentary structures caused by wave and current action.

Gradient

Measure of how steep a slope is. The greater the gradient the steeper a slope is. The smaller the gradient the shallower a slope is.

Understanding Organic Rocks

Organic rocks are formed from the accumulation and lithification of organic matter, such as the remains of plants or animals. These rocks can be further classified as either coal (from the accumulation of plant matter) or oil shale (from the accumulation of organic-rich mud).

Understanding the Use of Radioactive Decay within Absolute Age Dating

Radioactive decay is the process by which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. This process can change the number of protons and/or neutrons in the nucleus, leading to the formation of a different element. Absolute age dating is a method used to determine the age of rocks and other geological materials based on the decay of radioactive isotopes. Radioactive isotopes are atoms that have an unstable nucleus and undergo radioactive decay over time. By measuring the ratio of parent isotopes to daughter isotopes in a sample, scientists can determine how much time has elapsed since the rock or mineral was formed.

Siliciclastic

Sediment formed from clastic particles produced by the weathering of rocks and physically deposited by running water, wind, or ice.

Weathering

The chemical and physical processes that break down rock at Earth's surface.

Laminae

Sediments that form in thin layers.

Understanding Shape

Shape refers to the form of the individual particles that make up sediment. The standard classifications for shape are angular, rounded, and well-rounded. Angular particles have sharp edges and corners, rounded particles have smooth edges and rounded corners, and well-rounded particles have very smooth edges and are almost perfectly spherical in shape.

Understanding Siliciclastic Rocks

Siliciclastic rocks are made up of clasts (pieces) of preexisting rocks that have been weathered and transported by wind, water, or ice. These clasts can range in size from tiny particles of clay to larger sand, silt, or gravel. Examples of siliciclastic rocks include sandstone, shale, and conglomerate.

Understanding Sorting

Sorting refers to the uniformity of grain size within a sediment sample. A well-sorted sediment sample has particles that are all roughly the same size, while a poorly sorted sample contains a range of different particle sizes. Moderately sorted samples fall somewhere in between these two extremes.

Understanding Terrestrial Environments

Terrestrial environments: Terrestrial environments include all land-based depositional environments such as deserts, floodplains, alluvial fans, and glacial environments. Sedimentary rocks formed in these environments are typically characterized by the presence of well-rounded pebbles and sand grains, which have been transported and sorted by wind or water.

Drainage Basin

The area from which a single stream or river and its tributaries drains all of the water.

Relief

The difference in elevation between the highest and lowest parts of an area.

Sorting

The distribution of grain size of sediments, either in unconsolidated deposits or in sedimentary rocks.

Elevation

The height of land above sea level.

Parent Isotope

The isotope that undergoes radioactive decay.

Mantle

The layer of hot, solid material between Earth's crust and core.

Half-Life

The length of time required for half of the radioactive atoms in a sample to decay.

Understanding the Theory of Plate Tectonics

The lithosphere is divided into several large plates, as well as many smaller ones, that move relative to each other at rates of a few centimeters per year. These movements are driven by convection currents in the mantle.

Transport

The movement of material across the Earth's surface by water, wind, ice or gravity.

Decay

The natural process by which organic or inorganic substances break down over time through various physical, chemical, and biological processes.

Daughter Isotopes

The new isotopes produced by parent isotopes decaying, smaller and more stable.

Crossbedding

The patterns in sedimentary rocks left by wind-blown or water-washed sediments.

Color

The perceived shade of a mineral.

Fossil Succession

The principle of fossil succession states that fossils occur in a definite and predictable order in sedimentary rocks. This allows scientists to use fossils to determine the relative age of rock layers. Fossils that are found in the same layer are assumed to be of the same age, while those in different layers are assumed to be of different ages.

Superposition

The principle of superposition states that in an undisturbed sequence of rock layers, the oldest layer is at the bottom and the youngest layer is at the top. This principle is based on the observation that sedimentary rocks are usually deposited in a continuous sequence, with the oldest layer being at the bottom and the youngest at the top.

Subduction

The process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary.

Chemical weathering

The process that breaks down rock through chemical changes.

Lithification

The process that converts sediments into solid rock by compaction or cementation.

Seafloor Spreading

The process that creates new sea floor as plates move away from each other at the mid-ocean ridges.

Understanding Transform Plate Boundaries

These boundaries occur when two plates slide past each other horizontally. Transform boundaries are associated with earthquakes, but they typically do not produce volcanic activity. The most famous transform boundary is the San Andreas Fault in California.

Understanding Divergent Plate Boundaries

These boundaries occur when two tectonic plates move away from each other, creating new crust. Divergent boundaries can occur on land or under the ocean, and they are associated with volcanic activity and earthquakes. Examples of divergent boundaries include the Mid-Atlantic Ridge and the East African Rift Zone.

Understanding Convergent Plate Boundaries

These boundaries occur when two tectonic plates move towards each other, and one plate is forced beneath the other in a process called subduction. Convergent boundaries can occur between two continental plates, between an oceanic and a continental plate, or between two oceanic plates. Convergent boundaries are associated with volcanic activity, earthquakes, and the formation of mountain ranges. Examples of convergent boundaries include the Andes Mountains, the Himalayas, and the Cascadia Subduction Zone.

Cross-Cutting Relationships

This principle states that any geological feature that cuts across a rock layer must be younger than the layer it cuts through. Examples of such features include faults, dikes, and veins.

Inclusions

This principle states that any rock fragment or fossil found within a rock layer must be older than the layer it is found in. This principle is based on the assumption that the fragment or fossil was present in the rock layer that it was derived from, and was subsequently incorporated into the younger rock layer.

Original Horizontality

This principle states that sedimentary rocks are deposited in horizontal layers that are parallel to the Earth's surface. Any deviation from this position indicates that the rock has been disturbed or deformed after deposition.

Ocean-Continent Convergent Boundary

This type of convergent boundary occurs where an oceanic plate collides with a continental plate. The denser oceanic plate subducts beneath the lighter continental plate, forming a deep ocean trench. As the subducting plate sinks deeper, it generates magma that rises up to create a volcanic arc on the continental plate. The Andes Mountains in South America are an example of an ocean-continent convergent boundary.

Continent-Continent Convergent Boundary

This type of convergent boundary occurs where two plates carrying continental crust collide. Unlike oceanic crust, continental crust is too buoyant to subduct, so the plates crumple and fold, creating high mountain ranges. The Himalayas in Asia are an example of a continent-continent convergent boundary.

Ocean-Ocean Convergent Boundary

This type of convergent boundary occurs where two plates carrying oceanic crust collide. One plate usually subducts or sinks beneath the other, forming a deep ocean trench. As the subducting plate sinks deeper into the mantle, it generates magma that rises to the surface to create volcanic islands or a volcanic arc. The Aleutian Islands in Alaska are an example of an ocean-ocean convergent boundary.

Clast

To break; surgical fracture.

Understanding Transitional Environments

Transitional environments: Transitional environments are those where marine and terrestrial environments meet, such as deltas, lagoons, and beaches. Sedimentary rocks formed in these environments often display a mixture of marine and terrestrial characteristics, such as mudstones with ripple marks and cross-bedding, or sandstones with fossil shells.

Biosratigraphy

Uses the fossils of different organisms to date and correlate rock layers.

Continental Collision

When two continental plates collide pushing the continental crust up to form mountains.

Angular Unconformity

Where horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers, producing an angular discordance with the overlying horizontal layers.