Weathering Processes PDF

**WEATHERING** **★ AGENTS OF WEATHERING** **○ Water --** In liquid form, it seeps into cracks and crevices of rocks when the temperature drops, it freezes and definitely will expand in the form of ice. **○ Salt --** Saltwater sometimes gets into the cracks and pores of rocks. When it evaporates,...

**WEATHERING** **★ AGENTS OF WEATHERING** **○ Water --** In liquid form, it seeps into cracks and crevices of rocks when the temperature drops, it freezes and definitely will expand in the form of ice. **○ Salt --** Saltwater sometimes gets into the cracks and pores of rocks. When it evaporates, salt crystals are left behind and grow in the cracks and pores which cause pressure on the rock and slowly break it apart. **○ Temperature --** The process is called thermal stress. Rock tends to expand with heat and contract with low temperature. As this happens repeatedly, the structure of the rock weakens and over time crumbles. **○ Plants --** When the seed of the tree being spread in the environment sprouts in soil that has collected in a cracked rock. As the roots grow, the wider the cracks, eventually breaking the rock into pieces. Overtime, trees can break apart even large rocks. Even small plants, such as mosses, can enlarge tiny cracks as they grow. **○ Animals --** Animals that tunnels underground, such as moles and prairie dogs, also work to break apart rock and soil. Other animals digs and tramples rock aboveground, causing rock to slowly crumble. **★ TYPES OF WEATHERING** **❀ PHYSICAL WEATHERING --** caused by the effects of changing temperatures on rocks, causing the rock to break apart. **○ Abrasion -** occurs when rocks surface is frequently exposed to water. **○ Freeze-thaw --** occurs when water continually seeps into cracks, freezes, and expands, eventually breaking the rock apart. **○ Exfoliation --** occurs when cracks develop parallel to the land surface as a consequence of reduction in pressure during uplift and erosion. **❀ CHEMICAL WEATHERING --** caused by rainwater reacting with the mineral grains in rocks to form new minerals (clays) and soluble salts. These reactions occur particularly when the water is slightly acidic, **○ Carbonation --** carbon dioxide dissolves in rainwater and becomes weakly acidic. This weak "carbonic acid" can dissolve limestone as it seeps into cracks and cavities. Over many years, solutions of the rock can form spectacular cave systems. **○ Hydrolysis** -- the breakdown of rock by acidic water to produce clay and soluble salts. Hydrolysis takes place when acid rain reacts with rock-forming minerals such as feldspar to produce clay and salts that are removed in solution. **○ Hydration** -- a type of chemical weathering where water reacts chemically with the rocks, modifying its chemical structure. **○ Oxidation** -- the breakdown of rock by oxygen and water, often giving iron- rich rocks a rusty-colored weathered surface. **❀ BIOLOGICAL WEATHERING -** Biological weathering of rocks occurs when rocks are weakened by different biological agents like plants and animals. When plant roots grow through rocks, it creates fractures and cracks that result eventually to rock breakage. **○ Physical Means -** Burrowing animals like shrews, moles and earthworms create holes on the ground by excavation and move the rock fragments to the surface. Furthermore, humans also indirectly contribute to biological weathering by different activities that cause rocks to break. **○ Chemical Compounds** - Some plants and animals also produce acidic substances that react with the rock and cause its slow disintegration. **○ HYDRATION** - - **❀ MECHANICAL WEATHERING** - - ---------------------Galing Somewhere------------------ **EARTH\'S INTERNAL HEAT SOURCE** **Inner Core --** it is the hottest layer of the earth that is above 9000 Fahrenheit and it is 1250 km thick. ------------------------------------------------------------ **★ Convection Current** occurs in the air, ocean, and the mantle. It is caused by a differing proximity to a heat source. The difference in temperature relates directly to the density of the material, causing the effect. **Convection current** occurs by areas of a liquid or gas heating or cooling greater than their surroundings, causing differences in temperature. Hot rocks are less dense and rise in a gravitational field while relatively cold rocks are more dense and sink. The rise of hot rocks advects heat upward while the fall of cold rocks advects cold downward; this counterflow is equivalent to an upward heat flux. **★ TYPES OF MELTING** **❀ Partial Melting -** takes place because rocks are not pure materials. As temperature rises, some minerals melt and others remain solid. If the same conditions are maintained at any given temperature, the same mixture of solid and melted rock is maintained. **❀ Flux Melting -** happens if a rock is close to its melting point and some water or carbon dioxide is added to the rock, the melting temperature is reduced and partial melting starts. **❀ Decompression - t**akes place within Earth when a body of rock is held at approximately the same temperature but the pressure is reduced. This happens because the rock is being moved toward the surface, either at a mantle plume (a.k.a., hot spot), or in the upwelling part of a mantle convection cell. If a rock that is hot enough which is close to its melting point is moved toward the surface, the pressure is reduced, and the rock can pass to the liquid side of its melting curve. At this point, partial melting starts to take place. **METAMORPHISM** **★ Metamorphism -** is one of the geologic processes in which rocks change in form, composition, and structure due to intense heat and pressure and sometimes with the introduction of chemically active fluids. It takes place tens of kilometers below the surface where temperatures and pressures are high enough to transform rock without melting it. The increase in temperature and pressure and change of the chemical environment can change the mineral composition and crystalline textures of the rock while remaining solid all the while. The metamorphic rocks under these change conditions depend on the original rock chemistry, the exact pressures, and temperature to which rocks are subjected, and the amount of water available for chemical reaction. **★ FACTORS AFFECTING METAMORPHISM** **❀ TEMPERATURE:** The heat affects the rock's chemical composition, mineralogy, and texture. For instance, during burial metamorphism, at a depth of about 8 to 15 kilometers from the surface of the crust, metamorphic reactions begin. The rocks adjust to the new temperature causing their atoms and ions to recrystallize and form new arrangements thereby creating new mineral assemblages. During recrystallization, new crystals grow larger than the crystals in the original rock. The rate at which temperature increases with depth in the Earth's crust is known as **geothermal gradient** which varies on plate tectonic settings like the thickness of the crust or whether the area is in the subduction zone between oceanic and continental or under the converging two continental crusts. **Subduction zones**, for instance, are characterized by low temperature metamorphism, and the area at which collision takes place between two converging crustal plates is characterized by high-temperature metamorphism. **❀ PRESSURE:** It changes the composition, mineralogy, and texture of rocks. Pressure is different in various tectonic settings, like temperature. For instance, metamorphism in the subduction zone is characterized by **high-pressure metamorphism**. In contrast, the collision zone between two continental crusts is marked by **moderate-pressure metamorphism.** **TWO TYPES OF PRESSURES KNOWN ALSO AS STRESSES THAT EXERT FORCE ON ROCKS CAUSING CHANGES** **The vertical stress or confining pressure** is the stress or pressure exerted on the rock by the weight of overlying material such as in burial metamorphism. This type of pressure is the same in all directions and makes the rocks fracture or deform. **The directed or differential pressure** is imposed by a force in a particular direction. Differential pressure is dominant at convergent boundaries where plates move towards each other and collide thus exerting force and cause rocks to deform. Pressure causes rocks to form folds in a particular direction as directed by the pressure, thus directed pressure guides the shape and orientation of the new crystals formed as minerals recrystallize under the influence of both heat and pressure. This results in a textural change such that the minerals are elongated in the direction perpendicular to the directed stress and this contributes to the formation of **foliation.** **Foliation** is a set of flat or wavy parallel cleavage planes produced by deformation under directed pressures. In the figure below, the effect of compression due to pressure aligns the minerals as they recrystallize during metamorphism. **Hydrothermal fluids** also play a role in metamorphism. The dissolved minerals in the fluids react with rocks causing changes in chemical and mineral compositions and sometimes completely replacing one mineral with another without changing the textures of the rocks. This type of metamorphism is known as **metasomatism** in which the alteration process is caused by fluids passing through the rock and catalyzing chemical reactions. **★ TYPES OF METAMORPHISM** - - - - - - **Guide Question: If rock starts with shale into slate and into phyllite, do you think it increases its metamorphic grade? Why?** - **Guide Question: How is magma formed? What are the factors affecting it?** - - **ROCK BEHAVIOR AND STRESS** - - - **Guide Question: What are folds? (Anticline, Monocline, Syncline)** - - - - **Guide Question: What is fault? (Normal, Reverse, Strike Slip)** **Faults** -- A rock under ample stress can crack, or fracture. The fracture is called a joint because there is a block of rock left standing on either side of a fracture line. The **footwall** is the rock that is placed on top of the fault, while the **hanging wall** is below the fault. - - - **SEAFLOOR SPREADING** **Harry Hess --** a geophysicist who studies the deepest parts of the ocean floor. He explained how the convection currents in the Earth's interior make the seafloor spread. **Seafloor Spreading -** a geologic process in which tectonic plates -- large slabs of Earth's lithosphere -- split apart from each other. It is a result of mantle convection in which Convection current carries heat from the molten materials in the mantle and core towards the lithosphere. This current ensures that the "recycled" materials formed in the lithosphere were back to the mantle. The magma moves up from the mantle and erupts as pillow lava. This forms a new oceanic crust at the ridge. Then, as a new oceanic crust forms, it pushes the older crust aside. This means that the nearer the ocean floor to the oceanic ridge, the younger it is compared to the ones farther from the ridge. This crust eventually subducts at the deep ocean trenches and melts back into the mantle. Then the seafloor spreading continues as a "recycling" process. **Mid-Ocean Ridge --** it forms when seafloor spreading happens in which the magma rises up to the earth's surface. This happens when the oceanic crust diverges that leaves an opening. The movement of the seafloor causes the magma rises up in which when it is cooled down, it forms a mid-ocean ridge. **STRUCTURE AND EVOLUTION OF OCEAN BASINS** **Continental shelf**- Partly shallow extension of the continent underwater. **Continental slope-** Transition zone of continental shelf and deep ocean floor. It starts from oceanic crust to continental crust. **Continental rise-** It is where the ocean begins. All basaltic and oceanic rocks are found here. It is the place where the sediments from land are washed. The continental margin starts from continental shelf up to continental rise. **Abyssal plain-** The flattest part of the ocean. 50 % of the earth's surface is covered by this plain. **Island-** It's not just a piece of land floating up in the middle of the sea, it is part of the ocean basin that extends up from the ocean floor. **Seamount-** It is an undersea mountain. The erosion caused by waves destroyed the top of a seamount which caused it to be flattened. **Trench-** It is the deepest part of the ocean. **Mid-oceanic ridge-** The seafloor mountain system which is situated in the middle of the ocean basin. It is where upwelling of magma happens which causes the sea floor to spread. **MOVEMENT OF PLATES** 1\. What is Magma Intrusion **Magma Intrusion --** as the denser tectonic plate subducts, or sinks below, or the less-dense tectonic plate, hot rock from below can intrude the cooler plate above. 2\. Why is the rim of Pacific Ocean called as the Ring of Fire? - 3\. What is Manila Trench? **Manila Trench --** an active convergent plate margin between the South China Sea and the Northern Philippines. **H. Stratified Rocks** **1. Law of Superposition** is a basic law of geochronology, stating that in any undisturbed sequence of rocks deposited in layers, the youngest layer is on top and the oldest on bottom, each layer being younger than the one beneath it and older than the one above it. **2. Law of Original Horizontality** was first proposed by Danish geological pioneer Nicholas Steno in the 17th century. The law states that layers of sediment were originally deposited horizontally under the action of gravity. It suggests that all rock layers are originally laid down (deposited) horizontally and can later be deformed. This allows us to infer that something must have happened to the rocks to make them tilted. **3. The Law of Lateral Continuity** states that the layers of rock are continuous until they encounter other solid bodies that block their deposition or until they are acted upon by agents that appear after deposition takes place such as erosion and fault movements. **DETERMINING AGE OF ROCKS** **RELATIVE DATING** is the technique used to determine the age by comparing the historical remains to the nearby layers. It is a less advanced technique when compared to absolute dating. Some methods used in relative dating are stratigraphy, biostratigraphy, and cross-dating. **TYPES OF RELATIVE DATING:** **1. Stratigraphy:** This technique assumes that the lowest layer is the oldest while the topmost layer is the youngest layer. It is one of the oldest methods of relative dating. **2. Biostratigraphy:** In this technique, the faunal deposits such as fossils of dead animals are used to establish a strategy for dating. It is an extended version of the stratigraphy **3. Cross dating:** In this method, the fossils of one layer are compared with another layer with known dating. **4. Fluorine dating:** Bones from fossils absorb fluorine from the groundwater. The amount of fluorine absorbed indicates how long the fossil has been buried in the sediments **Absolute Dating** is a technique that determines the exact numerical age of a historical remaining. Since it evaluates the exact age of the sample, absolute aging is also called numerical dating. The four techniques used in absolute dating are radiometric dating, amino acid dating, dendrochronology, and thermoluminescence. **TYPES OF ABSOLUTE DATING:** **1. Radiometric dating:** It determines the age of the sample by measuring the amount of a particular radioactive isotope present in the sample. The age can be determined by the rate of decay of that isotope. The type of radioactive isotope used depends on the type of sample. One of the most popular and widely used types of a radioactive isotope in this type of technique is carbon14. **2. Amino acid dating:** The change in the protein content of a biological sample can be used to determine the age. A particular form of living being may have a defined protein content in their bodies that deteriorates with time. **3. Dendrochronology:** The number of annual growth rings of a dicot is used in this technique to determine the age of the tree. **4. Thermoluminescence:** It determines the period during which certain object was last subjected to heat. It is based on the concept that heated objects absorb light and emit electrons. The emissions are measured to compute the age **INDEX FOSSIL AND GEOLOGIC TIME SCALE** **Stratigraphy:** The oldest dating method which studies the successive placement of layers. It is based on the concept that the lowest layer is the oldest and the topmost layer is the youngest. **Geologic Time Scale --** divides up the history of the earth based on life-forms that have existed during specific times since the creations of planet. A system of chronological dating that relates geological strata to time. It is used by geologists, paleontologists and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history **A. EONS.** It has the largest intervals of geologic time. A single eon covers a period of several hundred million years. The history of the Earth has been divided into three eons: Archaean, Proterozoic and Phanerozoic. **Archaean Eon** -- it is the period where life first formed on Earth, archea and bacteria. Earth cooled down and was able to support continents and oceans. **Proterozoic Eon --** it is the period just before the proliferation of complex life on Earth. There were extensive shallow epicontinental seas and rocks are less metamorphosed than Archean age. **Phanerozoic Eon --** it is the period of visible life where rapid expansion and evolution of life forms occur and fill the various ecological niches available on Earth. The time between Earth's formation and the beginning of the Paleozoic era are often collectively called the Precambrian time or also known as the "time of hidden life". This era ranges from 4.6 billion years ago when the Earth formed to about 544 million years ago when abundant microscopic life appeared. **B. ERA.** It is the subdivision of eons. The geologic time scale is divided into three eras -- Paleozoic (time of ancient life), the Mesozoic (time of middle life) and the Cenozoic (time of recent life).  **C. PERIODS AND EPOCHS**. Each era is further divided into periods and further into epochs. **Cambrian Period** - Almost all marine organisms came into existence as evidenced by abundant fossils. One important event is the develop yent of organisms having the ability to secrete calcium carbonate and calcium phosphate for the formation of shells. The evolution of chordates, animal with dorsal nerve cord, hard resembled clams and arthropods ancestors of spiders, insects and crustaceans. There were two supercontinents during this period, Gondwana and Laurentia. **Ordovician Period** - This period marked the earliest appearance of vertebrates and the jawless fish known as Agnatha. Ordovician rocks have distinction of occurring at the highest elevation on Earth -- the top of Mount Everest. During this period, the level of carbon dioxide was several higher than today. There were four major continents separated by three major oceans **Silurian Period -** This period brought the emergence of terrestrial life, the earliest well developed circulatory system (vascular plants) known as Cooksonia. As plants move ashore so did other terrestrial organisms. Airbreathing scorpions and millipedes were common during the period. Romundina, a primitive armoured fish with a cartilage skeleton is the earliest fish known to have jaws. Three northern continents collided forming the new supercontinent Euramerica. **Devonian Period** - This period was known as the "age of fishes". Lowland forests of seed ferns, scale trees and true ferns flourished. Sharks and bony fishes developed. Today the lung fishes and coelacanth, a "living fossil" have such internal nostrils and breathe in a similar way. The first amphibians made their appearance, although able to live on land, they need to return to water to lay their eggs. The Kellwasser Event was largely responsible for the demise of the great coral reefs, jawless fishes and trilobites. **Carboniferous Period** - Warm, moist climate conditions contributed to lash vegetation and dense swampy forests. Insects under rapid evolution led to such diverse forms of giant cockroaches and dragonflies. The evolution of the first reptiles took place with the development of the amniotic egg, a porous shell containing a membrane that provided an environment for embryo. The Coal Age, the formation of organic deposits of coal in plant debris formed the world's first extensive coal deposits. **Permian Period** - A dramatic climatic shift may have been partially triggered the assembly of smaller continents into a supercontinent, Pangea which was surrounded by an immense ocean called Panthalassa. The reptiles were well-suited to their environment that they ruled the Earth for 200 million years. The two major groups of reptiles -- diapsids and synapsids dominated this period. Diapsids gave rise to the dinosaurs while synapsids gave rise to mammals **THE MESOZOIC ERA** - known as the age of reptiles, Mesozoic Era is made up of three periods: Triasic, Jurassic and Creataceous. The most significant event was the rise of the dinosaurs. A famous Jurassic deposit is the Morrison Formation, within which the world's richest storehouse of dinosaurs was preserved. True pines and red woods appeared and rapidly spread. Flowering plants arose and their emergence accelerated the evolution of insects. A major event of this era was the breakup of Pangea. At the end of this era, the dinosaurs and reptiles were completely wiped out. **THE CENOZOIC ERA** - this era is known as the "age of mammals" because mammals replaced the reptiles as the dominant land animal. It is also sometimes called the " age of flowering plants" because angiosperms replaced gymnosperms as the dominant land plants. This era is made up of two periods: Tertiary and Quartenary. From oldest to youngest the periods are broken up into the Paleocene, Eocene, Oligocene, Miocene and Pliocene for the Tertiary period and the Pleistocene and Holocene for the Quarternary period. **Petrification --** is the process by which organic material becomes a fossil through the replacement of original material and the filling of the original pore spaces with minerals. **FOUR GEOLOGIC TIMES:** Precambrian/Cambrian Palezoic Mesozoic Cenozoic **THREE PERIODS OF MESOZOIC ERA AND EPOCH:** **Triassic --** earliest period of Mesozoic era of geological history marked by the first appearance of dinosaurs. It is known as **"Ages of Reptiles"** **Jurassic --** is the second to the three period of Mesozoic. It is defined as a warm, wet climate that gave rise to lush vegetation and abundant life. It is known for the **"Golden Time of Dinosaurs"** **Creataceous** -- it is the last and longest period of Mesozoic era that is known for **"Ages of Dinosaurs"** **Kell Wasser Event -** saw the extinction of the beloceratid and maticoceratid goniatite groups, many conodont species, most colonial corals, several groups of trilobites, and the atrypid and pentamerid brachiopods at the Fransnian-Famennian Boundary.