Earth Science Weathering Processes (PDF)

**[Quarter 2- Module 1]{.smallcaps} Weathering** **[What is exogenic process?]{.smallcaps}** Exogenic processes break down rocks and erode rock fragments from higher energy sites, transporting them to locations of lower energy. The geomorphic agents are flowing water, wind, moving ice or waves. *...

**[Quarter 2- Module 1]{.smallcaps} Weathering** **[What is exogenic process?]{.smallcaps}** Exogenic processes break down rocks and erode rock fragments from higher energy sites, transporting them to locations of lower energy. The geomorphic agents are flowing water, wind, moving ice or waves. **[What is weathering?]{.smallcaps}** Weathering is the *breaking down of rocks and other materials on Earth's surface*. It is a slow but continuous process affecting all substances exposed to the atmosphere. **[What are the types of weathering?]{.smallcaps}** 1\. *Mechanical/Physical* *weathering* disintegrates rocks, breaking smaller fragments from a larger block or outcrop of rock without changing their chemical composition. **[Five principal types of physical weathering:]{.smallcaps}** *a.* Unloading occurs when overlying material, such as soil or another rock stratum, is removed (most commonly through erosion) and restricting pressure on the underlying rock is decreased. In response, the rock generally fractures into sheets which lie perpendicular to the direction in which pressure is released. Since the most common occurrence is the removal of a horizontal layer of material above the rock, the results of unloading are often seen as sheets of rock which lie parallel to the surface topography. *b*. Exfoliation is a process in which large flat or curled sheets of rock fracture and are detached from the outcrop due to pressure release. As erosion removes the overstrain from a rock that formed at high pressure deep in the Earth ́s crust, it allows the rock to expand, thus resulting in cracks and fractures along sheet joints parallel to the erosion surface. *c.* Thermal expansion and contraction weathering as any material is heated, it expands. As it cools, it contracts. In materials like rocks with many crystals, this expansion and contraction can cause mechanical fracturing. It is useful to consider not simply that the whole rock expands and contracts, but that the individual crystals making it up do so as well. In a rock such as granite, where many different minerals exist and are oriented in many different directions, the effect of crystal expansion is of great importance. *d.* Freeze-thaw weathering occurs when rocks are porous (contain holes) or permeable (allow water to pass through). When water freezes, it expands in volume up 9%, and this can cause large pressures to be exerted on the walls and bottom of the crack, widening it and eventually leading to a piece of rock breaking off. *e.* Salt crystal growth, water containing liquefied salts accumulates in these spaces. When the water evaporates, the salts stay behind developing into crystals that are capable of wedging pieces of rock apart. 2\. *Chemical weathering*, ions from a rock are either released into water or recombine with other substances to form new materials, such as clay mineral. **[Agents of chemical weathering:]{.smallcaps}** *a.* Oxidation, water has regular contact with the atmosphere contains plenty of oxygen. Water can dissolve most of the minerals present in rocks. It can form acids when it combines with some of the gases in the air to produce a different kind of mineral. For example, feldspar reacts with water to form clay. *b.* Solution, a chemical reaction causes mineral-forming ions to dissociate and the separated ions are carried away in the water. Rock salt, which contains the mineral halite (NaCl), is susceptible to dissolution in water. Most minerals that are insoluble or only slightly soluble in pure water will dissolve more readily if the water is acidic. *c.* Carbonation, It is a common type of solution that involves carbon dioxide and water molecules reacting with, and thereby decomposing, rock material. This is most effective on carbonate rock (those containing CO3), particularly limestone, which is an abundant sedimentary rock composed of calcium carbonate (CaCO3). *d.* Hydrolysis, water molecules alone, rather than oxygen or carbon dioxide in water, react with chemical components of rock-forming minerals to create new compounds, of which the H+ and OH- ions of water are a part. *e.* Acids and chemicals from organisms. Living organisms perform chemical reactions to obtain minerals from soil and rocks. They combine with rainwater to form sulfuric acid. Sulfuric acid is stronger than carbonic acid. It easily corrodes rocks, metals, and other materials. Many chemical changes are possible. Lichens can have a profound effect on rock. Lichens, a combination of algae and fungi, produce a weak acid that can dissolve rock. Plant roots are also an important source of chemical weathering. As roots expand into rock, acids can change the minerals in the rock. Plant roots also use carbon dioxide, thus changing the composition of the soil. **[What is erosion and sedimentation?]{.smallcaps}** Erosion is the transport by wind, water and ice of soil, sediment and rock fragments produced by the weathering of geological features. Sedimentation occurs when eroded material that is being transported by water, settles out of the water column onto the surface, as the water flow slows. The sediments that form a waterway\'s bed, banks and floodplain have been transported from the catchment and deposited there by the flow of water. Estuaries are shaped by the mixing of water and sediments from both a waterway and the ocean, creating complex sedimentary environments. **[Agents of erosion and sedimentation:]{.smallcaps}** *a.* Wind is the most active agent of erosion in deserts, open fields, and beaches. In these places, loose materials are abundant and can be easily picked up and carried by the wind. The amount of rock and soil that can be blown away by the wind depends on its speed. The faster the wind blows, the more particles it can carry. The particles that it can no longer carry are deposited as dunes and loess. *b.* Waves constantly erode and shape the shoreline. The shoreline is where the body of water and land meet. Waves carry large amounts of sand, rock particles, and shells. These solid particles are deposited in other parts of the shoreline. Thus, creating beaches consist of fine sand or large pebbles are carried by waves to the shores of seas and lakes. Sandbars are submerged or partly exposed ridge of sand or coarse sediment that is built by waves offshore from beach. Spits are elongated ridge of sand that stretches from the land to the mount of nearby bay. *c.* Running water is the most efficient and effective agent for erosion. From falling raindrops to rushing rivers, streams and runoff. The runoff water that flows towards the stream and rivers. Stream or river can carry large amounts of sediments. When the flow of rivers and streams slows down, sediments are deposited. Large sediments usually settle on the riverbed while smaller ones are deposited along river banks forming lakes, alluvial fans, deltas, flood plains, and levees. *d.* Ice as glacier moves along a valley, it carries with rock debris, such as large boulders and smaller particles. The moving glacier scrapes away and creates grooves into rocks as it moves, creating various surface features. **[How do rocks and soil move downslope due to the action of gravity?]{.smallcaps}** Mass wasting it is a collective term for the downslope transport of surface materials in direct response to gravity. This gravitational force is represented by weight of each object. Heavier objects have a greater downward pull from gravity than lighter objects. The force of gravity encourages rock, sediment, and soil to move downhill on sloping surfaces. Examples of mass wasting are landslide, mudflow, debris flow, avalanche, and slump. **[Quarter 2 -- Module 2:]{.smallcaps}** **Week 2 Endogenic Processes** **Endogenic Processes Part 1** We will always remember that everything on Earth got a place. All that is being washed away eventually settles down then rise again. **Instructions:** Study the diagram below then provide correct answer on a separate sheet of paper to the guide questions that follows. For those who have internet access you may opt to visit the link to review how far you knew Earth's structure and the rock cycle. Caution: Be sure to closely follow netiquette guidelines. A screenshot of a computer screen Description automatically generated  A screenshot of a computer Description automatically generated **[Significance of the Rock Cycle]{.smallcaps}** The Earth's crust undergoes gradual but continuous change of rock components as presented by the rock cycle (Figure 1). There are two forces that make rock cycle to occur one is the Earth's internal heat engine that moves material around in the core and the mantle through convection (Figure 2). It leads to slow but significant changes within the crust. The other is the water cycle which is the movement of water, ice and air at the surface powered by the sun. The Earth's core is hot enough to keep the mantle moving for the rock cycle to occur. Earth's atmosphere is thick and there is the presence of liquid water. When core is no longer hot enough to drive mantle convection and there is no atmosphere or liquid water like on some other planets or their satellites the rock cycle is practically gone. **[Sources of the Earth's Internal Heat]{.smallcaps}** One source of heat in the deep Earth is the remaining heat from when the planet first formed is the primordial heat (early formation of the solar system). In the process of planetary growth (accretion) and surface restructuring in which collision events played a major role large amounts of heat are generated as the objects collide and stick together. As the Earth grew heavier, its gravitational field increased, and it began to compact because of the growing mass of largely unconsolidated material. The compaction also produces frictional heating, caused by denser core material sinking to the center of the planet. As heavier elements like iron sunk to the core carrying other elements that bind to it. Chemical process takes place that gives off heat as heavy elements like iron and nickel goes deep towards the core separates from silicon and oxygen in the mantle during the core formation. Pressure and temperature increase with depth in a planetary body, so minerals that are stable at one depth might not be stable at another depth. The heat generated in the core produces the magnetic field strong enough to shield the planet from the solar wind. The heat that escapes out into the mantle, causes convection in the rock that moves crustal plates and fuels volcanoes. Another source responsible for the initial heating of planetary evolution are the short-lived radioisotopes that are found in nature continuously created or replaced by natural processes, such as cosmic rays, background radiation, or the decay chain or spontaneous fission of other radionuclides. The Earth would have cooled off gradually and become a dead rocky globe with a cold iron ball at the core if not for the continued release of heat by the decay of radioactive elements like potassium-40, uranium-238 and thorium-232, which have half-lives of 1.25 billion, 4 billion and 14 billion years, respectively. The most important heat-generating process involved in planetary differentiation is radioactive decay. Rocks are insulating materials, so heat is transferred by conduction very slowly to the surface where it is transferred by radiation off to space. Because of this slow rate of heat transfer, various parts of a planet's interior will become heated to the point of partial melting. When a magma is formed and brought into other regions of the planetary body (usually upward into overlaying layers) heat is carried by convection due to the movement of the molten material. Volatile elements and compounds, such as water, carbon dioxide, sulfur, etc., improve the transfer of heat by convection. Radiogenic heat is made during the decay of these radioactive isotopes. **[Geothermal gradient]{.smallcaps}** The geothermal gradient is the amount that the Earth's temperature increases with depth.It indicates heat flowing from the Earth's warm interior to its surface. Typically the temperature increases by 25 0C for every kilometer of depth. This difference in temperatures drives the flow of geothermal energy and allows humans to use this energy for heating and electricity production. There are a number of places on the planet where the temperature changes quite a bit faster though, and those locations are almost always where geothermal is the most sustainable. The interior of the Earth is extremely hot, and reaches temperatures over 5000 OC near the core, which is not much colder than the surface of the Sun. Below shows (Figure 4 and Figure 5) how temperature decreases as it approaches Earth's surface, along with the mechanisms of heat flow. Overall, temperature changes are gradual except near base of the mantle where extreme compositional changes occur, and in the lithosphere where the existence of fluids has a large effect.  Heat transfer mechanisms in the Earth \... Figure 4. Temperature profile of the Earth's layer. Figure 5. Heat transfer mechanisms within the Earth, along with % amount of heat flow in each layer Based on the geotherm curve (Figure 4) it can be obtained that the mantle is considerably hotter than crust, and the core is much hotter than the mantle. Internal heat of the Earth transports through conduction, convection (mantle convection and hydrothermal convection), and volcanic advection (Figure 5). Heat of the inner core due to radioactive decay is being transferred through conduction to the outer core. Convection occurs at the mantle but not between the core and mantle or even between the asthenosphere and lithosphere (except at seafloor spreading zones). The only heat transfer mechanism in this transition zone is through conduction. Advection usually occurs at the boundary of the plate (Figure 2). Conduction and advection both mechanisms are present in convection.  [Significance of magma]{.smallcaps} 1\. The mineral deposits extracted from Earth are carried by magma to shallower depth. 2\. Deep magma is the main agent that brings all the key ingredients for life (water and carbon) to the surface of the Earth. Crust and mantle are almost entirely solid indicating that magma only forms in special places where pre-existing solid rocks undergo melting. **[Three Ways of Magma Formation]{.smallcaps}** 1\. *Decompression melting* melting due to decrease in pressure The decrease in pressure affecting a hot mantle rock at a constant temperature permits melting forming magma. When pressure is decreased, melting can occur because the bonds between the particles can be broken down and move farther away from each other. 2\. *Flux melting* melting caused by addition of volatiles When volatiles such as water mixes with hot, dry rock, the volatile decreases the rock's melting point. It helps break the chemical bonds in the rock to allow melting. 3\. *Heat transfer melting* melting resulting from heat transfer of rising magma Rising magma transfers heat to surrounding rocks at shallower depths. **[Locations of Magma Formation]{.smallcaps}** Subduction zones are formed when an oceanic plate is pushed under another plate. Flux melting occurs when water mixes with hot rocks as the lower plate moves down. A diagram of a rock formation Description automatically generated How does magma behave? Density contrast: magma is less dense than the surrounding country rock (rock native to the area). Magma rises faster when the difference in density between the magma and the surrounding rock is greater. Magma at deeper levels passes through mineral grain boundaries and cracks in the surrounding rock. When enough mass and buoyancy is attained, the overlying surrounding rock is pushed aside as the magma rises. Depending on surrounding pressure and other factors, the magma can be spewed to the Earth's surface or rise at shallower levels underneath. When at shallower levels, magma may no longer rise because its density is almost the same as that of the country rock. The magma starts to accumulate and slowly solidifies. Viscosity: a measure of a fluid's resistance to flow. Magmas with low viscosity flow more easily than those with high viscosity. Temperature, silica content and volatile content control the viscosity of magma. The table below shows the effects of different factors on magma viscosity. A screenshot of a computer Description automatically generated *How temperature and pressure affect the mineral content in rocks?* Bowen's reaction series Certain minerals are stable at higher melting temperature and crystallize before those stable at lower temperatures. Crystallization in the continuous and discontinuous branches takes place at the same time. Continuous branch: contains only plagioclase feldspar, with composition changing from calcium-rich to sodium rich as temperature drops. Discontinuous branch describes how ferromagnesian minerals in the magma are transformed as temperature changes. The early formed crystals, olivine in this case, reacts with the remaining melt as the magma cools down, and recrystallizes into pyroxene. Further cooling will transform pyroxene into amphibole. If all the iron and magnesium in the melt is used up before all of the pyroxene recrystallizes to amphibole, then the ferromagnesian minerals in the solid rock would be amphibole and pyroxene and would not contain olivine or biotite.  *Important concepts derived from the Bowen's reaction series:* A mafic magma will crystallize into pyroxene (with or without olivine) and calcium-rich plagioclase ̶that is, basalt or gabbro ̶if the early formed crystals are not removed from the remaining magma. Similarly, an intermediate magma will crystallize into diorite or andesite, if early formed minerals are not removed. If minerals are separated from magma, the remaining magma is more felsic than the original magma. For example, if olivine and calcium-rich plagioclase are removed, the residual melt would be richer in silicon and sodium and poorer in iron and magnesium. When rocks are heated in high temperatures, minerals will melt in reverse order, going up the series in the Bowen's reaction series diagram. Quartz and potassium feldspar would melt first. If the temperature is raised further, biotite and sodium-rich plagioclase would contribute to the melt. Any minerals higher in the series would remain solid unless the temperature is raised further. *Different processes by which the composition of magma may change* Magmatic differentiation is the process of creating one or more secondary magmas from single parent magma Adapted from Teaching Guide for Senior High School: Earth Science, The Commission on Higher Education in collaboration with the Philippine Normal University,2016 Figure 12. Bowen's Reaction Series Page 13 of 19 Earth Science 1\. Crystal Fractionation--a chemical process by which the composition of a liquid, such as magma, changes due to crystallization. There are several mechanisms for crystal fractionation. One that is directly related to the Bowen's reaction series is crystal settling. Crystal settling - denser minerals crystallize first and settle down while the lighter minerals crystallize at the latter stages. Bowen's reaction series shows that denser minerals such as olivine and Ca-rich plagioclases form first, leaving the magma more felsic. 2\. Partial Melting- as described in Bowen's reaction series, quartz and muscovite are basically formed under low temperature conditions, making them the first ones to melt from the parent rock once exposed in higher temperature and/or pressure. Partial melting of an ultramafic rock in the mantle produces a basaltic magma. 3\. Magma mixing -- this may occur when two different magma rises up, with the more buoyant mass overtakes the more slowly rising body. Convective flow then mixes the two magmas, generating a single, intermediate (between the two parent magmas) magma. 4\. Assimilation/contamination of magma by crustal rocks - a reaction that occurs when the crust is mixed up with the rising magma. As magma rises to the surface, the surrounding rocks which it encounters may get dissolved (due to the heat) and get mixed with the magma. This scenario produces change in the chemical composition of the magma unless the material being added has the same chemical composition as the magma. SOURCES OF THE EARTH'S INTERNAL HEAT The Earth's internal heat comes from primordial and radioactive heat. Primordial heat is leftover heat from the collision of particles and the rearrangement of materials when Earth was still developing into a planet. Radioactive heat comes from energy released by the decay of uranium-235, uranium-238, potassium-40, and thorium-232 found in the crust and mantle. Convection in the mantle redistributes heat from the core closer to the Earth's surface. During convection, hotter rocks rise, and cooler rocks sink. MAGMATISM Magma is liquid rock under the Earth's surface. Mafic magma is low in silica and contain darker minerals. Felsic magma is higher in silica and contain lighter colored minerals. Magma forms from the partial melting of rocks from the mantle or crust. Partial melting is the melting of some parts of the rock only. This happens because the rocks are made up of different minerals, each of which has a different melting point. Magma is generated through decompression melting, flux melting, and heat transfer melting. Decompression melting occurs when a hot body of rock experiences a decrease in pressure by moving towards the surface. Flux melting takes place when flux, a substance that decreases melting temperature, is added to a hot body of rock. Water and other volatiles act as flux. Heat transfer melting is the partial melting of rocks at shallower depths caused by heat coming from rising magmas. Magma forms in divergent boundaries, hotspots, and subduction zones. Divergent boundaries are formed when two tectonic plates move away from each other. Hotspots are hot areas inside the Earth made by rising hot materials from deep within the mantle. Subduction zones are formed when the collision of tectonic plates pushes an oceanic plate under another plate. A screenshot of a computer Description automatically generated **[Quarter 2 - Module 3]{.smallcaps}** **Metamorphism and Rock Deformation** Metamorphic rocks make up a large part of the Earth\'s crust and form 12% of the Earth\'s land surface. Some examples of metamorphic rocks are gneiss, slate, marble, schist, and quartzite. These rocks are formed through the process called metamorphism. **Metamorphism** is the change of minerals or geologic texture in pre-existing rocks or parent rock called **protolith.** In metamorphism, the protolith does not melt into liquid magma. An igneous or sedimentary rock changes to metamorphic rock because of heat, pressure, and the introduction of chemically active fluids. This occur because some minerals are stable only under certain conditions of pressure and temperature. When pressure and temperature change, chemical reactions occur to cause the minerals in the rock to change to an assemblage that is stable at the new pressure and temperature conditions. The outcome of metamorphism depends on pressure, temperature, and the abundance of fluids involved, and there are many settings with unique combinations of these factors. Some types of metamorphism are characteristic of specific plate tectonic settings, but others are not. The types of metamorphism are burial, regional, subduction, contact and dynamic. - Burial metamorphism occurs when sediments are buried deeply enough that the heat and pressure cause minerals to begin to recrystallize and new minerals to grow but does not leave the rock with a foliated appearance. As metamorphic processes go, burial metamorphism takes place at relatively low temperatures (up to \~300 °C) and pressures (100s of m depth). - Regional metamorphism is referred to as large-scale metamorphism, such as what happens to continental crust along convergent tectonic margins (where plates collide). It occurs when large areas of rocks are subjected to differential stress for long periods of time that is often associated with mountain building. Mountain building commonly occurs in subduction zones and at collision zones. The force of the collision causes rocks to be folded, broken, and stacked on each other, so not only is there the squeezing force from the collision but also from the weight of stacked rocks. Rocks that form from regional metamorphism are likely to be foliated because of the strong directional pressure of converging plates. **[Subduction Metamorphism]{.smallcaps}** At subduction zones, where ocean lithosphere is forced down into the hot mantle, there is a unique combination of relatively low temperatures and very high pressures. The high pressures are to be expected, given the force of collision between tectonic plates, and the increasing lithostatic pressure as the subducting slab is forced deeper and deeper into the mantle. **Contact metamorphism** happens when a body of magma intrudes into an adjacent body of rock, specifically an igneous rock. When this takes place the temperature of the existing rock rises and also becomes infiltrated with fluid from magma. The intrusion is usually in a small area called the metamorphic or contact aureole. Contact metamorphism is often referred to as high temperature, low pressure metamorphism because the temperature difference between the surrounding rock and the intruded magma is larger at shallow levels in the crust where pressure is low. Heat is important in contact metamorphism, but pressure is not a key factor, so contact metamorphism produces non-foliated metamorphic rocks such as hornfels, marble, and quartzite. **Dynamic metamorphism** is the result of very high shear stress such as that one which occurs along fault zones. It occurs at relatively low temperatures compared to other types of metamorphism and consists predominantly of the physical changes that happen to a rock experiencing shear stress. It affects a narrow region near the fault, and rocks nearby may appear unaffected. At lower pressures and temperatures, it will have the effect of breaking and grinding rock creating cataclastic rocks while at higher pressures and temperatures, grains and crystals in the rock may deform without breaking into pieces. Prolonged dynamic metamorphism due to high temperature and high pressure produces a rock called mylonite, in which crystals have been stretched into thin ribbons. Because of metamorphism, rocks transform into denser, more compacted rocks. There are two types of metamorphic rocks. They are foliated and non-foliated metamorphic rocks. Foliated metamorphic rocks are banded or having striped appearance and are often associated with regional metamorphism while non-foliated rocks lack foliation or are not banded and are often associated with contact metamorphism. ***Lesson 2: Rock Deformation*** Rock deformation is a process of changing a rock due to stress or heat. There are different types of deformation that occur in rocks. In this lesson, we are going to tackle the differential stresses that leads to the deformation in rocks. Before we move on, do not forget to answer the word search below and find out the potential active faults in Cebu City. Ready? Let us start. Potentially Active Faults. The following images are part of the Active Faults Map of Cebu City generated by PHIVOLCS-DOST. The broken lines represent the approximate trace of potentially active faults in Cebu City. According to PHIVOLCS-DOST, a potentially active fault shows an insufficient evidence that the fault moved in the last 10,000 years. However, the possibility of movement along these types of faults may not be discounted. This map may be revised as new information become available.  STRESS Stress on rocks is the force applied per unit area. The force is mostly related to the movement of tectonic plates and to the weight of overlying rocks. STRAIN Strain is the resulting deformation because of stress. A strain is a change in size, shape, or volume of a material or any kind of movement of the rocks. Rocks under low confining pressures near the earth's surface generally deform through fracturing and faulting. Rocks deep within the crust under high confining pressures deform by folding. A screenshot of a computer Description automatically generated Stages of Rock Deformation: 1\. Elastic Deformation takes place when a rock stretches but return to its original shape. 2\. Ductile Deformation happens when the rock will permanently change in shape after being bent or folded. 3\. Irreversible Deformation occurs when the rock will permanently change in shape and size due to breaking or fracturing. Factors that Affect Rock Deformation 1\. Confining Pressure: At high confining pressures materials are less likely to fracture because the surrounding area tends to hinder formation of fractures. 2\. Temperature: At high temperature rock molecules and their bonds can move, thus, materials will behave in a more ductile manner. 3\. Strength of Rock: The kind of mineral present in the rocks affect the strength of the rock. The presence of water also affects the strength of the rock. 4\. Strain Rate: High strain rate materials tend to fracture while low strain rate materials tend to be ductile. FOLDING The bending of rocks when forces are applied on it at opposite directions is called folding. It is common along convergent plate boundaries and usually resulting to mountain building. Deep within the crust, as plates collide, rocks bend or crumple into folds. Once they are folded, they do not return to their original shape. Figure 6 shows the parts of rock folds. The anticline is the upfold which will begin as ridges while the syncline is the downfold which will begin as valleys.  FAULTING The process of causing a fracture or break in a rock due to shear stress is called faulting. This can result to earthquakes. A fracture is a simple break that does not involve significant movement of the rocks on either side. If the rocks on one or both sides of a fracture move, the fracture is called a fault. A fault is a boundary between two bodies of rock along which there has been relative motion. The San Andres fault in California corresponds to the transform boundary between two continental plates. There are three types of faults namely normal fault, reverse fault and strike-slip fault. Normal fault is a dip-slip fault in which the block above the fault has moved downward relative to the block view. The extensional stress creates a space when two blocks of crust pull apart forming a valley. The East African Rift Zone is an example where there is normal faulting going on. Reverse fault is also known as thrust fault. It is a dip-slip fault in which the upper block, above the fault plane, moves up and over the lower block. The vertical movement of the crustal blocks is due to compressional stress. This type of fault commonly takes place in convergent boundaries like that in the Himalayas and Rocky Mountains. A strike slip fault, on the other hand, is due to the shearing or the sliding of rocks. The Philippine Fault Zone (PFZ)is an example of a strike slip fault which is 1,200 km-long and stretches from northwestern Luzon to southeastern Mindanao. Below shows the comparative behavior of faults.  **[Quarter 2-Module 4]{.smallcaps}** **Seafloor Spreading and Plate Tectonics** **Lesson 1 -- Seafloor Spreading** The idea of Wegener that the continents were once joined together but now separated would imply that something had to be put between the continents for them to move apart. What could have pushed them to split, and drift can be linked to the theory of seafloor spreading. Perform the given activities and read the discussions that follow to understand the ideas about seafloor spreading.