Lecture 28 Earth’s Interiors. Erosion. Earthquakes Structure of the Earth’s Types of Erosion Chapter 14.6  14.14

Three Types of Rock There are 3 types of rock according to their origin. Igneous rocks - rocks cooled from a molten state.molten Volcanic origin. 2/3 of rocks in crust are igneous. Sedimentary rocks - materials derived from other rocks and deposited by water, wind, or glacial ice.ice Make 8% of the crust, but 3/4 of the surface rocks. Metamorphic rocks - igneous or sedimentary rocks that have been changed (metamorphosed) by heat and pressure deep under the Earth’s surface.under

Sedimentary Rocks Sediments are deposited by water, wind, or ice, and become rocks through the pressure of the overlying deposits. The sedimentary rocks have nearly rounded grains that do not grow, like crystals of igneous rocks. There are two groups of sedimentary rocks: fragmental rocks and (bio)chemical precipitates. Fragmentals: conglomerate (wide variety of sizes), sandstone (small grains), shale (soft rock, consolidated mud). Precipitates: limestone (chemical precipitate or shell fragments), chalk (loosely consolidated variety of limestone), chert (microcrystalline quartz, used as tools by earlier people).

Metamorphic Rocks Both igneous and sedimentary rocks can be changed under high temperatures and pressures inside the Earth. Some minerals become unstable and form new substances by chemical reactions; others grow more as crystals. Many metamorphic rocks show a property called foliation.property This is the arrangement of flat or elongated mineral grains in parallel layers due to a high pressure in one direction. Examples: Slate  produced at low temperatures from shale, is harder that shale, and usually black or dark. Schist  formed at high temperatures from shale or fine- grained igneous rocks, has large visible grains.

Earthquakes An earthquake consists of rapid vibrations of rocks near the the surface. Single shocks may last for a few seconds. Severe quakes may last for up to 3 minutes. There is about 1 million earthquakes every year.year Only ~15 of them are violent. Most earthquakes are caused by sudden movement of large blocks of the crust (<70 km from the surface) along fracture lines called faults.called Magnitude of earthquakes are measured on the Richter scale.scale

Structure of the Earth Rocks on both sides of the fault vibrate and send out waves. Body waves travel through the Earth’s interior. Surface waves travel along the surface. There are 2 types of both body and surface waves.types Body waves: P (longitudinal) and S (transverse). Surface waves: Love (transverse) and Rayleigh (transverse). Propagation of seismic waves registered by seismographs all over the Earth allows to learn about its interior structure.seismographs structure A different view of the Earth’s structure.different

Erosion Erosion is a process of wearing rocks down. Its main reason is gravity. Main agents of erosion are water, ice, and winds. Disintegration by rainwater and air is called weathering. There are 2 types of weathering: chemical (by chemical reactions) and mechanical (by temperature changes in the presence of water or by wind).chemicalwind Running water of streams and rivers introduces stream erosion. Motion of ice in glaciers introduces glacial erosion.glacial

Sedimentation Materials transported by the erosion agents are eventually deposited to form sediments. The ultimate destination of the debris is ocean. The material is carried toward the ocean in stages. It can be stored on the river banks (alluvial fans, river delta) or at places of old glaciers (moraine).fans deltamoraine Groundwater can deposit materials in the pore spaces of sediments, which are eventually converted to rocks. Dissolved materials precipitate in cracks to form veins. StalactitesStalactites and stalagmites are examples of groundwater depositions.stalagmites

Summary There are only 3 different types of rocks according to their origin: igneous, sedimentary, and metamorphic. The Earth is still heated by radioactive elements which exist in its core since the formation time. The internal heating is responsible for Earth’s geological activity, including earthquakes. Erosion is an important process changing rocks on Earth due to the presence of the atmosphere.