🏝️Earth Science Unit 3 – Earth's Surface Processes

Key Concepts and Terminology

• Weathering breaks down rocks and minerals through physical, chemical, and biological processes
• Erosion involves the transport of weathered material by agents such as water, wind, and ice
• Deposition occurs when eroded sediments settle out of the transporting medium and accumulate
• Topography refers to the shape and features of Earth's surface, including mountains, valleys, and plains
• Geological time scale divides Earth's history into eons, eras, periods, and epochs based on major events and changes in life forms
• Plate tectonics describes the movement and interaction of Earth's lithospheric plates, which shapes the planet's surface features
• Geomorphology studies the processes that shape Earth's surface and the resulting landforms
• Sedimentary rocks form through the deposition and lithification of sediments, often in layers

Earth's Structure and Composition

• Earth is composed of three main layers: crust, mantle, and core
  • Crust is the thin, outermost layer composed of solid rocks (oceanic and continental crust)
  • Mantle is the thick, middle layer composed of hot, dense rock (upper and lower mantle)
  • Core is the innermost layer, consisting of a liquid outer core and a solid inner core
• Lithosphere comprises the crust and uppermost mantle, forming rigid plates that move over Earth's surface
• Asthenosphere is a portion of the upper mantle that exhibits plastic flow due to high temperatures and pressures
• Tectonic plates are large, irregularly shaped sections of the lithosphere that move and interact with each other
• Plate boundaries are zones where tectonic plates meet, resulting in various geologic processes (divergent, convergent, and transform boundaries)
• Rocks are classified into three main types based on their formation: igneous, sedimentary, and metamorphic

Weathering and Erosion

• Physical weathering involves the breakdown of rocks through mechanical processes without changing their chemical composition
  • Freeze-thaw weathering occurs when water seeps into cracks, freezes, and expands, causing the rock to break apart
  • Thermal expansion and contraction can cause rocks to crack due to temperature changes
  • Abrasion occurs when rocks and particles collide or scrape against each other, wearing them down
• Chemical weathering involves the alteration of rock composition through chemical reactions with water, air, or other substances
  • Carbonation occurs when carbon dioxide dissolves in water, forming carbonic acid that reacts with rocks (limestone)
  • Hydrolysis involves the reaction of water with minerals, breaking chemical bonds and forming new compounds (feldspar)
  • Oxidation occurs when oxygen reacts with minerals, often forming rust-like substances (iron-rich rocks)
• Biological weathering is caused by the actions of living organisms, such as plant roots growing in cracks or acids produced by lichens
• Erosion agents include water (rivers, waves, and glaciers), wind, and gravity (mass wasting)
• Factors influencing erosion rates include climate, rock type, vegetation cover, and topography

Sediment Transport and Deposition

• Sediment transport involves the movement of weathered material from its source to a site of deposition
• Fluvial transport occurs when sediments are carried by rivers and streams
  • Bed load consists of larger particles that roll, slide, or bounce along the river bed
  • Suspended load includes smaller particles that are carried within the water column
  • Dissolved load consists of ions and molecules that are dissolved in the water
• Aeolian transport involves the movement of sediments by wind, often in arid environments (sand dunes)
• Glacial transport occurs when sediments are carried by glaciers, either within the ice or on its surface (moraines)
• Longshore drift is the transport of sediments along a coastline due to the action of waves and currents
• Deposition occurs when the energy of the transporting medium decreases, allowing sediments to settle
  • Deltas form where rivers deposit sediments as they enter a standing body of water (Mississippi River Delta)
  • Alluvial fans develop where streams emerge from confined valleys onto a flatter plain
  • Beaches and barrier islands result from the deposition of sediments along coastlines

Landforms and Topography

• Landforms are natural features on Earth's surface that result from various geomorphic processes
• Mountains form through tectonic processes, such as plate collisions (Himalayas) or volcanic activity (Andes)
  • Fold mountains develop when sedimentary layers are compressed and deformed by tectonic forces
  • Fault-block mountains form when blocks of crust are uplifted or downdropped along faults
  • Volcanic mountains are created by the accumulation of lava and volcanic debris around a vent
• Valleys are low-lying areas between higher elevations, often formed by erosion from rivers or glaciers
  • V-shaped valleys develop through the erosive action of rivers in steep terrain
  • U-shaped valleys are carved by glaciers, characterized by steep walls and a flat bottom
• Plains are extensive, relatively flat areas that can form through various processes
  • Coastal plains develop from the deposition of sediments along continental margins
  • Alluvial plains form from the deposition of sediments by rivers in their floodplains
  • Plateaus are elevated, flat-topped landforms that result from the uplift and erosion of horizontal rock layers
• Coastlines are shaped by the interaction of various processes, such as wave action, tides, and sea-level changes
  • Cliffs and headlands form where resistant rocks are eroded more slowly than surrounding areas
  • Bays and estuaries develop where the coastline is indented, often at the mouths of rivers
  • Barrier islands are elongated, offshore deposits of sand that parallel the coastline

Geological Time and Rock Formation

• The geological time scale divides Earth's history into eons, eras, periods, and epochs based on major events and changes in life forms
  • Eons represent the longest divisions of time (Phanerozoic, Proterozoic, Archean, Hadean)
  • Eras are subdivisions of eons, characterized by distinct life forms and global conditions (Cenozoic, Mesozoic, Paleozoic)
  • Periods are subdivisions of eras, often named after geographic locations or dominant life forms (Quaternary, Cretaceous, Jurassic)
  • Epochs are subdivisions of periods, reflecting more specific changes in climate and life forms (Holocene, Pleistocene)
• Relative dating determines the order of events in Earth's history without assigning specific ages
  • Principle of superposition states that in an undeformed sequence of sedimentary rocks, the oldest layers are at the bottom
  • Principle of cross-cutting relationships indicates that a geologic feature that cuts across another must be younger
  • Principle of original horizontality assumes that sedimentary layers are deposited in a nearly horizontal position
• Absolute dating assigns specific ages to events or rocks using radiometric techniques
  • Radioactive decay of isotopes (carbon-14, uranium-235) provides a clock for measuring the age of rocks and organic materials
• Rock cycle describes the continuous process of rock formation, transformation, and destruction
  • Igneous rocks form from the cooling and solidification of magma or lava (granite, basalt)
  • Sedimentary rocks form through the deposition and lithification of sediments (sandstone, limestone)
  • Metamorphic rocks form when pre-existing rocks are subjected to high temperatures and pressures (marble, gneiss)

Human Impact on Earth's Surface

• Urbanization and infrastructure development alter natural landscapes and drainage patterns
  • Construction of buildings, roads, and parking lots increases impervious surfaces, leading to increased runoff and erosion
  • Channelization of rivers and streams can disrupt natural sediment transport and deposition processes
• Agriculture and deforestation can accelerate soil erosion and alter sediment loads in rivers
  • Removal of vegetation exposes soil to the direct impact of raindrops and wind
  • Tillage practices can break up soil aggregates and increase vulnerability to erosion
  • Overgrazing by livestock can reduce vegetation cover and compact soil, reducing infiltration and increasing runoff
• Mining and quarrying activities can significantly alter local topography and drainage patterns
  • Removal of rock and soil can create pits, spoil piles, and unstable slopes prone to erosion and mass wasting
  • Acid mine drainage can occur when exposed sulfide minerals react with water and air, contaminating nearby water sources
• Coastal development and engineering structures can interfere with natural coastal processes
  • Seawalls and groins can disrupt longshore drift, leading to erosion downdrift of the structures
  • Dredging of channels and harbors can alter sediment transport patterns and affect the stability of nearby shorelines
• Climate change, influenced by human activities, can impact Earth's surface processes
  • Rising sea levels can lead to increased coastal erosion and inundation of low-lying areas
  • Changes in precipitation patterns can alter the frequency and intensity of floods and droughts, affecting erosion and sediment transport

Real-World Applications and Case Studies

• The Grand Canyon in Arizona, USA, is an iconic example of the power of fluvial erosion and the principle of superposition
  • The Colorado River has carved through layers of sedimentary rocks, exposing nearly 2 billion years of Earth's history
  • The canyon's steep walls and intricate side canyons showcase the effects of weathering and mass wasting
• The Nile Delta in Egypt demonstrates the importance of sediment transport and deposition in shaping coastal landscapes
  • The Nile River carries vast amounts of sediment from the interior of Africa to the Mediterranean Sea
  • The delta's fertile soils, resulting from millennia of sediment deposition, support intensive agriculture and a large population
• The Maldives, an island nation in the Indian Ocean, faces significant challenges due to rising sea levels and coastal erosion
  • The islands are composed of coral reefs and atolls, which are highly vulnerable to changes in sea level and ocean chemistry
  • Coastal protection measures, such as seawalls and beach nourishment, are being implemented to mitigate the impacts of erosion
• The Loess Plateau in China is an example of the effects of human activities on soil erosion and landscape degradation
  • The region's fine, wind-blown sediments (loess) are highly susceptible to erosion when vegetation is removed
  • Intensive agriculture and deforestation have led to severe soil loss, gully formation, and reduced agricultural productivity
• The Aral Sea in Central Asia illustrates the consequences of human interventions in natural hydrological systems
  • Diversion of rivers for irrigation has drastically reduced the sea's water level and surface area
  • The exposed lakebed is subject to wind erosion, creating dust storms and health hazards for nearby populations