geol120 - midterm 1
What are mafic and felsic rocks?
Chemically, mafic rocks are enriched in iron, magnesium and calcium and typically dark in color. In contrast, the felsic rocks are typically light in color and enriched in aluminum and silicon along with potassium and sodium. The mafic rocks also typically have a higher density than felsic rocks.
How can climate change and land-use change alter risks of natural hazards?
Climate change has the ability to make things such as hurricanes and storms more frequent and more deadly. For example, warmer ocean temperatures means more evaporation leading to hurricane formation once reaching the 80 degrees needed.
What are the basic types of plate boundaries?
Convergent plates, divergent plates, and transform boundaries.
What are important characteristics of the major rock types?
Properties that help geologists identify a mineral in a rock are: color, hardness, luster, crystal forms, density, and cleavage. Crystal form, cleavage, and hardness are determined primarily by the crystal structure at the atomic level. Color and density are determined primarily by the chemical composition.
What are the different types of minerals and their distinguishing features/structures?
A mineral is a solid material that forms by a natural process. A mineral can be made of an element or a compound. It has a specific chemical composition. Its chemical composition is different from other minerals. Each type of mineral has physical properties that differ from others. These properties include crystal structure, hardness, density, and color. For example, silver is a soft, shiny metal. Salt is a white, cube-shaped crystal. Diamond is an extremely hard, translucent crystal. A mineral is solid, inorganic, formed by natural processes, crystalline structure, and has distinct chemical formula
What are minerals, isotopes, atoms, and different types of chemical bonding?
A mineral is an element or chemical compound that is normally crystalline and that has been formed as a result of geological processes. each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element. the basic unit of a chemical element. There are three primary types of bonding: ionic, covalent, and metallic. Ionic bonding. Covalent bonding. Metallic bonding.
What are subduction zones, mid-oceanic ridge, and hot spots?
A subduction zone is the biggest crash scene on Earth. These boundaries mark the collision between two of the planet's tectonic plates. ... At a subduction zone, the oceanic crust usually sinks into the mantle beneath the lighter continental crust. A mid-ocean ridge or mid-oceanic ridge is an underwater mountain range, formed by plate tectonics. This uplifting of the ocean floor occurs when convection currents rise in the mantle beneath the oceanic crust and create magma where two tectonic plates meet at a divergent boundary. A hot spot is an intensely hot area in the mantle below Earth's crust. The heat that fuels the hot spot comes from very deep in the planet. This heat causes the mantle in that region to melt. The molten magma rises up and breaks through the crust to form a volcano.
What is acid mine drainage, where does it occur and what causes it?
Acid mine drainage is the formation and movement of highly acidic water rich in heavy metals. This acidic water forms through the chemical reaction of surface water (rainwater, snowmelt, pond water) and shallow subsurface water with rocks that contain sulfur-bearing minerals, resulting in sulfuric acid. The major culprits are the coal and gold mines, and because of their location in the upper portions of the Vaal River catchment, their footprint on the water supply is huge. Aside from metal and acid pollution, the major problem is the increase in dissolved salts into the Vaal River
How do we manage stormwater on campus? What is bioretention and why is it used? What are the goals of the stormwater management features that we visited?
Bioretention is an important technique that uses soil, plants and microbes to treat stormwater before it is infiltrated or discharged. It is used as a natural solution to treat stormwater that may contain high levels of salt or other contaminants. The goals of the stormwater management features that we visited are to prevent runoff that may damage infrastructure on campus.
What is the Bowen reaction series (no need to memorize!) - just know what it is and why it is useful from the lecture notes.
Bowen's Reaction Series describes the temperature at which minerals crystallize when cooled, or melt when heated. The low end of the temperature scale where all minerals crystallize into solid rock is approximately 700°C (158°F). Bowen's reaction series allows geologists to predict chemical composition and texture based upon the temperature of a cooling magma.Bowen's reaction series is able to explain why certain types of minerals tend to be found together while others are almost never associated with one another.
How have humans altered the nitrogen cycle and what are the consequences?
Burning fossil fuels, application of nitrogen-based fertilizers. Because of activities like this, increased global concentrations of greenhouse gases, increased transport of nitrogen by rivers into estuaries and coastal waters where it is a major pollutant.
What are the different forms of carbon in the carbon cycle and why do they each matter?
CO2, CH4, CO3-2, C, hydrocarbons, complex organic molecules. They all matter because most carbon is stored in rocks and sediments, while the rest is located in the ocean, atmosphere, and in living organisms. These are the reservoirs, or sinks, through which carbon cycles. Carbon is released back into the atmosphere when organisms die, volcanoes erupt, fires blaze, fossil fuels are burned, and through a variety of other mechanisms.
What are catastrophes and what causes them?
Damages to people, property, or society are sufficient that recovery or rehabilitation is a long involved process. Catastrophes can be caused by natural, man-made and technological hazards, as well as various factors that influence the exposure and vulnerability of a community.
What are some of the types of major features associated with different plate boundaries?
Deep ocean trenches, volcanoes, island arcs, submarine mountain ranges, and fault lines are examples of features that can form along plate tectonic boundaries.
What is the relationship between population growth and risks from natural hazards?
Direct relationship
What is Earth System Science and what is the Gaia hypothesis?
Earth System Science seeks a deeper understanding of the physical, chemical, and biological and human interactions that determine the past, current, and future states of the earth. The Gaia hypothesis is a theory that all living things have a regulatory effect on the Earth's environment that promotes life overall; the earth is homeostatic in support of life-sustaining conditions.
What are the characteristics of the Earth's internal structure?
Earth's interior is generally divided into three major layers: the crust, the mantle, and the core. ... The outer core is molten and liquid iron and nickel, while the inner core is solid and much more dense than either iron or nickel at the surface.
What is the internal structure of the Earth and its characteristics?
Earth's interior is generally divided into three major layers: the crust, the mantle, and the core. The hard, brittle crust extends from Earth's surface to the so-called Mohorovicic discontinuity, nicknamed the Moho. The Moho is not located at a uniform depth, but about 10 kilometers (6 miles) below the seafloor and about 35 kilometers (22 miles) beneath the surface of continents. The mantle is divided from the core by the Gutenberg discontinuity, about 2,880 kilometers (1,798 miles) beneath Earth's surface. The outer core is molten and liquid iron and nickel, while the inner core is solid and much more dense than either iron or nickel at the surface.
What is an ecosystem?
Ecosystem: A community of organisms and its nonliving environment in which chemical elements cycle and energy flows.
What are eutrophication and hypoxia and causes and implications?
Eutrophication is where a body of water becomes enriched with minerals and nutrients, particularly nitrogen and phosphorus. Hypoxia is a state in which oxygen is not available in sufficient amounts at the tissue level to maintain adequate homeostasis. Eutrophication is often caused when irrigation places fertilizer into rivers which dump all the nitrogen and phosphorus into one body of water, forming algae. This can lead to dead zones when the algae sink and decompose and absorb oxygen. Hypoxia is caused when the oxygen levels are not significant enough for the body to function properly and can lead to confusion.
What is the major cause of hypoxia in the Gulf of Mexico and Chesapeake Bay?
Eutrophication. This causes algal blooms in the Gulf of Mexico and the Chesapeake Bay. When these algae die, they decompose and sink to the bottom, creating a dead zone where there are extremely low levels of oxygen. This lack of oxygen leads to hypoxia in the Gulf of Mexico.
What are intrusive and extrusive igneous rocks?
Extrusive rocks are formed on the surface of the Earth from lava, which is magma that has emerged from underground. Intrusive rocks are formed from magma that cools and solidifies within the crust of the planet.
What is floodplain reconnection and why is it used in restoration?
Floodplains and their benefits to people and nature can be restored by getting water on the floodplain at the right time, in the right amount, and for the right duration to support natural floodplain habitats. They are used in restoration because they are extremely important and they provide clean water supplies, recreation opportunities, habitat for fish and wildlife, and when left undeveloped they safely convey flood water.
We discussed some definitions regarding forecasting, prediction, etc. and please review.
Forecast: includes ranges of certainty Prediction: specifying date, time, and size Risk: the probability of an event multiplied by consequences.
Review notes on case studies for freshwater salinization and nitrogen pollution
Freshwater salinization is the process of salty runoff contaminating freshwater ecosystems, which can harm aquatic species in certain quantities and contaminate drinking water. Denitrification causes algae to grow faster than ecosystems can handle, which reduces or eliminates oxygen in the water, leading to illnesses in fish and the death of a large number of fish.
How does urbanization alter hydrogrpahs
Human influences include covering land with impermeable surface - more runoff filling in floodplains raises flood level. Installing storm sewers channels water into streams removing surface vegetation decreases lag time.
How has the weather changed as a result of human activities?
Human activities have led to the release of carbon dioxide and other heat-trapping "greenhouse" gases in sufficient quantity to change the composition of the atmosphere, resulting in an accumulation of heat in the Earth's system, commonly referred to as "global warming".
What are hydrographs and what factors influence them under natural conditions
Hydrographs graph stream discharge over time. They are influenced by amount of water (rain or snow melt), rate water enters stream, runoff vs. infiltration, porosity, topography, saturation, and vegetation cover.
Why is population growth an environmental problem?
Increased extraction of resources from the environment. Increased pollutants.
What are strategies for restoring the Kissimmee River and Mississippi River and are they working?
Kissimmee River: This process involves altering the site to reestablish indigenous historical ecosystems. Mississippi River: This process involves stream restoration, leading to a reconnection to the riparian zone, which will then lead to increased denitrification and improved water quality.
How can we use seismology to learn about the internal structure of the Earth?
Knowing how the waves behave as they move through different materials enables us to learn about the layers that make up the earth. Seismic waves tell us that the earth's interior consists of a series of concentric shells, with a thin outer crust, a mantle, a liquid outer core, and a solid inner core. By carefully examining the seismic fronts and their propagation, the seismic wave tool illustrates how earthquakes can provide evidence that allows us to infer earth's interior structure.
What are wetlands?
Landscape features such as swamps, marches, bogs, or prairie potholes that are frequently or continuously inundated by water.
What are magnetic stripes and what do they mean?
Magnetic Striping is when the sea floor is spreading, and magma from the mantle is rising through the Earth's crust. That magma then turns into new crust, forming the "Oceanic Crust". When lava gets erupted at the mid-ocean ridge axis it cools and turns into hard rock. ... This creates a symmetrical pattern of magnetic stripes of opposite polarity on either side of mid-ocean ridges. These patterns of stripes provide the history of seafloor spreading.
What are the links between magnitude and frequency of disturbances
Magnitude: Intensity of a natural hazard in terms of the amount of energy released Frequency: Recurrence interval of a disastrous event Magnitude and Frequency: Generally an inverse relation between them More damages associated with hazards of moderate frequency and magnitudes Magnitude and Frequency: Largely controlled by natural factors Impact risk: Controlled by both natural and human factors Low magnitude and high frequency hazards not always destructive, a high magnitude one almost certainly catastrophic Commonly, most impact risks from natural processes of moderate magnitude and moderate frequency
How does metamorphism, volcanism affect rocks?
Metamorphic rocks form when rocks are subjected to high heat, high pressure, hot mineral-rich fluids or, more commonly, some combination of these factors. Conditions like these are found deep within the Earth or where tectonic plates meet. Earth movements can cause rocks to be deeply buried or squeezed. As a result, the rocks are heated and put under great pressure . They do not melt, but the minerals they contain are changed chemically, forming metamorphic rocks.
What types of plate boundaries occur at the: deepest part of the ocean, ridges, rift lakes, mountains
Mid-ocean ridges occur along divergent plate boundaries, where new ocean floor is created as the Earth's tectonic plates spread apart. As the plates separate, molten rock rises to the seafloor, producing enormous volcanic eruptions of basalt.
What is the process of denitrification and why is it important for water quality in ecosystems?
NO3 -> NO2 -> NO -> N2O -> N2 [anaerobic or heterotrophic (requires organic C)] It is important for water quality to avoid eutrophication and the development of algal blooms which can lead to dead zones in the water.
Where are most lakes located and why?
Natural lakes are generally found in mountainous areas, rift zones, and areas with ongoing glaciation. Canada, Russia, and northern countries have many lakes due to glacier recession leaving behind pools of water such as lakes.
What is ocean acidification - how is it caused and what are the effects?
Ocean acidification is caused by dissolution (carbon dioxide dissolves in the ocean). CO2 + H2O -> H2CO3- (carbonic acid) OR CO2 in atmosphere -> dissolved CO2 gas in ocean. The effects of ocean acidification cause the pH level to decrease and the ocean to become acidic. This can lead to the death of other species.
What are oxbow lakes and how do they form
Oxbow lakes are horseshoe shaped lakes that form when silt and clay deposits accumulate in former channel connections, essentially cutting off part of the river creating a lake.
How do sedimentary rocks form and what are different types?
Pieces of rock are loosened by weathering, then transported to some basin or depression where sediment is trapped. If the sediment is buried deeply, it becomes compacted and cemented, forming sedimentary rock. Clastic sedimentary rocks may have particles ranging in size from microscopic clay to huge boulders. There are three different types of sedimentary rocks: clastic, organic (biological), and chemical. Clastic sedimentary rocks, like sandstone, form from clasts, or pieces of other rock. Organic sedimentary rocks, like coal, form from hard, biological materials like plants, shells, and bones that are compressed into rock. Chemical sedimentary rocks, like limestone, halite, and flint, form from chemical precipitation. A chemical precipitate is a chemical compound—for instance, calcium carbonate, salt, and silica—that forms when the solution it is dissolved in, usually water, evaporates and leaves the compound behind.
What are residence times, mass balance approaches, pools, fluxes, steady state?
Residence times are the amount of water in a reservoir divided by either the rate of addition of water to the reservoir or the rate of loss from it. Mass balance approaches are about mixing fossil and recycled or renewable in our existing systems and processes while keeping track of their quantities and allocating them to specific products. Pools describe the storage spaces for energy and matter. Fluxes describe the movement of energy and matter between different pools. A steady state, the amount of input and the amount of output are equal.
What are riparian zones and why do they matter for water quality?
Riparian zones are the critical interface between soil and stream. Demonstrated ability to prevent pollutant movement from upland land uses into streams and coastal waters. Most work on removal of groundwater nitrate in agricultural watersheds.
What is a riparian zone and why/how are riparian zones impaired in response to urbanization?
Riparian zones are the critical interface between soil and stream. Demonstrated ability to prevent pollutant movement from upland land uses into streams and coastal waters. Most work on removal of groundwater nitrate in agricultural watersheds. Higher urban flows result in lower riparian water tables. Causes channel erosion, nonfunctional floodplain, dry riparian soils.
How can we better manage risks from flooding and climate change?
Risk analysis is important in understanding impacts resulting from hazards. We can better manage risks by being alert towards magnitude and frequency and learn how to adapt to climate change and the increasing severity of storms.
How is risk determined?
Risk: the probability of an event multiplied by consequences.
How can road salt affect these stormwater management features?
Road salt increases the salinization of the water bodies in which it ends up in. It has negative health effects on the environment and prevents growth of plants. It also is a year round problem, rather than just in the winter when road salt is primarily used.
What are sediments and why are they important in streams
Sediment is material moved by streams. Sediment is important because it leads to the formation of nutrient rich soils.
What are some limitations and a few challenges with managing urban stormwater on campus that we discussed?
Some limitations include space and funding. It may be difficult to get the money to make these stormwater management facilities also coupled with the fact that there needs to be ample room for these things to be built on.
What are species, communities, ecosystems, keystone species, climax communities?
Species: individuals capable of interbreeding. Community: populations of different species living in the same area. Ecosystem: A community of organisms and its nonliving environment in which chemical elements cycle and energy flows. Keystone species:Species with strong community effect, with an influence disproportionate to their abundance. Climax communities: An ecological community in which populations of plants or animals remain stable and exist in balance with each other and their environment.
How can stormwater management affect runoff and infiltration to manage the quantity and quality of urban waters?
Stormwater management makes it easier for runoff to be cleared from urban environments and supplies areas for infiltration to take place. This removes the excess water that has the potential to damage buildings and infrastructure.
What are key ecosystem services of streams, lakes, and wetlands?
Streams and wetlands can provide natural flood control, maintain water supplies, trap excess sediment, protect water quality, sustains downstream ecosystems, and maintain biological diversity. Healthy fresh waters are living, functional systems. Lakes provide valuable ecosystem services that they support include water storage and supply, the purification of water through the removal of excessive nutrients, contaminants, and sediments, carbon and nitrogen sequestration, food production in the form of invertebrates and fish, support of biodiversity in aquatic and nearby terrestrial habitats, flood control, and recreation.
What is sustainability?
Sustainability refers to the idea of conserving resources and limiting pollution to a level that the natural environment and humanity can handle.
What is the Moho, asthenosphere, mantle?
The division in the lithosphere between the crust and the mantle is called the Mohorovicic discontinuity, or simply the Moho. ... The asthenosphere is the denser, weaker layer beneath the lithospheric mantle. It lies between about 100 kilometers (62 miles) and 410 kilometers (255 miles) beneath Earth's surface. The mantle is the mostly-solid bulk of Earth's interior. The mantle lies between Earth's dense, super-heated core and its thin outer layer, the crust. The mantle is about 2,900 kilometers (1,802 miles) thick, and makes up a whopping 84% of Earth's total volume.
How can the oceans influence atmospheric carbon dioxide?
The oceans have the ability to store about 30% of what is released to the atmosphere and act as a major carbon reserve. Through dissolution, carbon dioxide from the atmosphere is dissolved in the ocean thus increasing the amount of carbon in the ocean but a decrease in atmospheric carbon.
What is seafloor spreading and the lines of evidence?
The formation of new areas of oceanic crust, which occurs through the upwelling of magma at mid ocean ridges and its subsequent outward movement on either side. Harry Hess's hypothesis about seafloor spreading had collected several pieces of evidence to support the theory. This evidence was from investigations of the molten material: Hess's discovery on the warmer temperature near the mid-atlantic ridge when he began ocean mapping, led to his evidence about the molten material underneath the ocean. Through seafloor drilling, Hess discovered rocks that were away from the mid-oceanic ridge were relatively older than the rocks near to it. The old rocks were also denser and thicker compared to the thinner and less dense rocks in the mid-oceanic ridge.
What are the major rock laws?
The four laws are the law of superposition, law of original horizontality, law of cross-cutting relationships, and law of lateral continuity
What is exponential growth?
The growth rate that becomes ever more rapid in proportion to the growing total number or size.
Why do lakes stratify and mix?
The most important actions causing lake mixing are wind, inflowing water, and outflowing water. Lake stratification is due to the change in water's density with temperature. Lake stratification is the circulation of warm water near the surface and cold water near in the deep.
What is the scientific method?
The scientific method is to 1) make observations that describe a problem 2) do background research 3) create a hypothesis 4) test with an experiment 5) procedure working 6) Analyze data and draw conclusions 7) Communicate results
What are p waves and s waves and how are they transmitted?
There are two types of seismic waves, primary waves and secondary waves. Primary waves, also known as P waves or pressure waves, are longitudinal compression waves similar to the motion of a slinky (SF Fig. 7.1 A). Secondary waves, or S waves, are slower than P waves. The motion of secondary waves is perpendicular to the direction of the wave travel, similar to the motion of vigorously shaking a rope. P and S waves travel through the planet Earth after an earthquake. Scientists studying the waves produced by earthquakes learned that Earth's core has separate liquid and solid layers. S waves do not travel through liquid, but P waves do.
Potential warning signs of earthquakes
There isn't any.
What specifically caused the Hurricane Katrina catastrophe?
There was no second tier protection to flood control. Hurricane Katrina exceeded the design criteria of the flood protection structure. Specifically, the state relied on the levees around New Orleans, that when the storm broke the levees it completely destroyed the town itself. Regional subsidence was faster than appreciated. Height of floodwalls were not adjusted to accommodate land subsidence.
When we see steam coming up through vents and in the ground on campus, where does this steam come from? Why is there steam?
This steam comes from water processing plants underground where the water is boiled to remove the contaminants. This steam then is used to spin a turbine and generate electricity.
Why are streams and rivers restored (e.g. Kissimmee River)?
To help save biodiversity and entire ecosystems. Streams and rivers also provide many benefits to humanity such as the ones listed in (1).
What were Wegener's major lines of evidence
To prove his idea, Wegener found 4 major pieces of evidence: • Shape • Fossils • Climates • Rocks. The causes of continental drift are perfectly explained by the plate tectonic theory. The evidence for continental drift included the fit of the continents; the distribution of ancient fossils, rocks, and mountain ranges; and the locations of ancient climatic zones.
What is uniformitarianism vs. catastrophism?
Uniformitarianism is a theory that changes in the earth's crust during geological history have resulted from the action of continuous and uniform processes. Catastrophism is the theory that changes in the earth's crust during geological history have resulted chiefly from sudden and violent and unusual events.
Why did the human population increase so rapidly in the second half of the twentieth century?
Updates in medicine, new technology, longer life-span, baby boom
How does chemical weathering of rocks affect water quality in streams, rivers, and the ocean (e.g. we discussed why we care about weathering)?
Water's chief effect in weathering is to wash away fragments broken off rocks using its considerable mass and flow properties so that new volumes of the material are exposed. Water is a solvent for some chemicals/minerals; it can dissolve those and carry them away. A second important effect is its ability to find its way into the smallest nooks and crannies and then to freeze, in which process it expands its volume under very high pressure, making cracks larger and breaking pieces entirely away from the original matrix.
What is weathering and how can it occur?
Weathering is the breaking down or dissolving of rocks and minerals on Earths surface. ... Water, ice, acids, salts, plants, animals, and changes in temperature are all agents of weathering. Once a rock has been broken down, a process called erosion transports the bits of rock and mineral away.
What was Wegener's theory and why was it accepted/rejected?
Wegener continental drift theory introduced the idea of moving continents to geoscience. He proposed that earth must have once been a single supercontinent before breaking up to form several different continents. It was not accepted because he suggested no mechanism for moving the continents.
What are distinguishing characteristics of wetlands?
Wetlands are pieces of the environment where there is presence of water at the surface or root zone, unique soil conditions, and vegetation adapted to wet conditions.
What are the characteristics of wetlands?
Wetlands are pieces of the environment where there is presence of water at the surface or root zone, unique soil conditions, and vegetation adapted to wet conditions.
littoral currents
created when a train of waves reach the coastline and release bursts of energy.
What are the 5 spheres?
geosphere, Anthrosphere, hydrosphere, biosphere, atmosphere.
What is isostasy and how does it relate to mountain building?
isostasy, ideal theoretical balance of all large portions of Earth's lithosphere as though they were floating on the denser underlying layer, the asthenosphere, a section of the upper mantle composed of weak, plastic rock that is about 110 km (70 miles) below the surface. Isostasy controls the regional elevations of continents and ocean floors in accordance with the densities of their underlying rocks. As erosion levels the mountains, the roots will rise up and asthenosphere will flow back under the roots. This is called isostatic adjustment. Thus mountain chains will continue to rise long after other orogenic processes have ceased. Isostatic adjustment can be likened to blocks of wood floating on water.
What are stable and radioisotopes and what are the principles applied to determining ages and sources of materials? We discussed some specific examples in class about how isotopes were used.
radioactive isotope, also called radioisotope, radionuclide, or radioactive nuclide, any of several species of the same chemical element with different masses whose nuclei are unstable and dissipate excess energy by spontaneously emitting radiation in the form of alpha, beta, and gamma rays. A brief treatment of radioactive isotopes follows. For full treatment, see isotope: Radioactive isotopes. Every chemical element has one or more radioactive isotopes. For example, hydrogen, the lightest element, has three isotopes with mass numbers 1, 2, and 3. Only hydrogen-3 (tritium), however, is a radioactive isotope, the other two being stable. More than 1,000 radioactive isotopes of the various elements are known. Approximately 50 of these are found in nature; the rest are produced artificially as the direct products of nuclear reactions or indirectly as the radioactive descendants of these products.
What is a rock and can you describe the rock cycle?
rock, in geology, naturally occurring and coherent aggregate of one or more minerals. The rock cycle is a concept used to explain how the three basic rock types are related and how Earth processes, over geologic time, change a rock from one type into another. Plate tectonic activity, along with weathering and erosional processes, are responsible for the continued recycling of rocks. Rocks are classified into three basic types based on how they are formed. Igneous - A rock formed by the cooling and crystallization of magma (molten rock) at or below the Earth's surface. Sedimentary - A rock formed as a result of the weathering process, either by compaction and cementation of rock mineral fragments, or the precipitation of dissolved minerals. Metamorphic - These rocks form as existing rocks are subjected to intense heat and/or pressure, usually over long periods of time. The rocks in display are meant to be viewed in a clockwise direction. As you walk, keep in mind that existing rocks may change through natural processes over geologic time, or event melt to form new rocks.