14.1 - 14.4: Geology and Earth Resources

• Earth is a dynamic planet

  1. core: interior composed of dense, intensely hot mental, generates magnetic field enveloping the earth

  2. mantle: hot, pliable layer surrounding the core, less dense than the core

  3. crust: cool, lightweight, brittle outermost layer, that floats on top of the mantle

  

• Tectonic Processes

• the upper mantle contains convection currents that break overlying crust into tectonic plates

• slide slowly across the earth’s surface

• ocean basins form where continents crack and pull apart

• magma forced up through the cracks forms new oceanic crust that piles up underwater in mid-ocean ridges

  • magma: molten rock

• earthquakes are caused by grinding and jerking as plates slide past each other

• mountain ranges pushed up at the margins of colliding plates

• when oceanic plates collide with a continental landmass, the continental plate will ride up over the seafloor and the oceanic plate will subduct down into the mantle where it melts

  • deep ocean trenches mark subduction zones

• Rocks and Minerals

• a mineral is a naturally occurring, inorganic, solid element or compound with a definite chemical composition and regular internal crystal structure

• a rock is a solid, cohesive, aggregate of one or more minerals

  • each rock has a characteristic mixture of minerals, grain sizes, and ways in which the grains are mixed and held together

• rock cycle: cycle of creation, destruction, and metamorphosis

  1. igneous

  2. sedimentary

  3. metamorphic

  

• igneous rocks

  • most common type of rock in the earth’s crust

  • solidified from magma extruded onto the surface of volcanic vents

    • quick cooling of magma produces fine-grained rocks (basalt)

    • slow cooling of magma produces coarse-grained rocks (granite)

• metamorphic rocks

  • preexisting rocks modified by heat, pressure, and chemical agents

  • chemical reactions can alter both the composition and structure of rocks

    • marble from limestone

    • slate from mudstone/shale

• weathering and sedimentation

  1. mechanical weathering: physical break-up of rocks into smaller particles without a change in chemical composition

  2. chemical weathering: selective removal or alteration of specific components that leads to weakening and disintegration of rock

     • oxidation

     • hydrolysis

  3. sedimentation: deposition of particles of rock transported by wind, water, ice, and gravity until they come to rest

• sedimentary rock

• Deposited materials that remain in place long enough, or are covered with enough material for compaction, may again become rock. (sandstone, shale)

  • Shaped by erosion. 

• Geomorphology is the study of the processes    that shape the earth’s surface and the structures they create.

• Humans shape the Earth’s surface more than any other single geomorphic process 

  • except plate tectonics

• geologic hazards

• Asteroid impact led to extinction of dinosaurs.

• Floods take the greatest number of lives 

• Wind causes the most property damage.

• Earthquakes - sudden movements of the Earth’s crust that occur along faults where one rock mass slides past another

  • Gradual movement - called creep or seismic slip

    • When friction prevents creep, stress builds up until eventually released with a sudden jerk

      • Point at which first movement occurs is called the epicenter

• earthquakes

  • Worst death tolls from earthquake occur when construction is poor.  Now buildings in earthquake zones are reinforced.

    • Most seismically active region in U.S. is west coast.

    • Largest earthquake recorded was in New Madrid, Missouri.

    • Tsunami can be generated by earthquakes

• volcanoes

• Volcanoes and undersea magma vents are the sources of most of the Earth’s crust.

  • Many of world’s fertile soils are weathered volcanic material.

  • Nuees ardentes - deadly clouds of hot gas and ash like those that destroyed Pompeii,  temperatures exceed 1000^oC,they move at 60 mph and can kill in minutes.

    • Mudslides often accompany eruptions.

  • Volcanic dust and sulfur emissions reduce sunlight and temperature around the globe.

• landslides

• Landslides are examples of mass wasting, in which geologic materials are moved downslope from one place to another.

  • Can be slow and subtle or swift as in rockslides and avalanches

• Road construction, forest clearing, cultivation, and building on steep, unstable slopes increase the frequency and damage done by landslides.

10.1 Soils and Watersheds

• Soil is a renewable resource that develops gradually through the weathering of rocks and the accumulation of organic material.

  • ABIOTIC

• The accumulation of topsoil is a very slow process.  Under the best circumstances it accumulates at a rate of about 1 mm/year.

• With careful management, soil can be replenished and renewed indefinitely.

• Most farming techniques deplete soil through erosion and removal of organic material.

• Severe erosion rates can exceed 25 mm soil /year

• Soil is a marvelous, complex substance; an entire ecosystem that is hidden to most of us. In general it has 6 components:

  • Sand and gravel

  • Silts and clays

  • Dead organic material

  • Soil fauna and flora

  • Water

  • Air

• Variation in the 6 components of soil can produce an almost infinite variety of soil types.

• Soil texture (the amount of sand, silt and clay in the soil) is the most important characteristic of soils.

  • Loam soils are considered best for agriculture because they are a mixture of sand, silt and clay.

  • Brazilian tropical soils are deeply weathered red clays which have little organic material. They hold few nutrients and water .

  • The rich, black soils of the central US are rich in nutrients and organic material and contain a mixture of sand, silt and clay to hold moisture well

• Grassland vs Rainforest Soils

• Soil bacteria, algae and fungi decompose leaf litter making recycled nutrients available to plants.

• A single gram of soil can contain hundreds of soil bacteria and 20 meters of tiny fungal strands.

• Tiny worms including nematodes process organic material and create air spaces as they burrow.

• Larger insects, spiders and mites loosen and aerate the soil as well.

• Mycorrhizal symbiosis, an association between plant roots and certain fungi.   The plant feeds the fungus and the fungus provides water and inorganic nutrients to the plant enhancing growth

  • symbiotic relationship

• Soils are stratified into horizontal layers called soil horizons.

  • Horizons taken together make up the soil profile.

    • O Horizon (Organic layer)

      • Leaf litter, most soil organisms and partially decomposed organisms

    • A Horizon (Surface soil)

      • Mineral particles mixed with organic material

      • sand, silt, clay dispersed for plants to use

    • E Horizon (Eluviated washed out)

      • Depleted of soluble nutrients

    • B Horizon (Subsoil) 

      • Often dense texture due to clays

    • C Horizon

      • Weathered rock fragments with little organic material 

      • Parent Material is the mineral material on which the soil is built, can be bedrock

  

• food comes from a horizon

• Because soils are so important to our survival, we identify soils largely in terms of the thickness and composition of their upper layers.

  • When water falls to the ground it does one of three things:

       - evaporate into the air as water vapor

       - percolate down through the soil and 

          become groundwater

       - run downhill off the land into streams

        - the area of land that catches water and drains into a particular body of water is called a watershed

    • High points in elevation form watershed boundaries

      • - Land use activities in a watershed can affect the water quality

        - For example, if the water flowing into a river first flows 

          across a road, the water will dissolve salt and other 

          pollutants on the road and carry them into the river. 

             - Other land use activities that can affect the quality of water 

        • Applications of pesticides and fertilizers

        • Large amounts of manure

        • Sewage

        • Toxic spills 

        - Pollution anywhere in a watershed will affect the water 

          quality downstream  

        - Impermeable surfaces increase the amount of water runoff