Earth Systems Exam 3

The Structure of Earth

• Understanding of Earth's structures based on minute fraction of total depth (less than 8 miles)

• Goode deal of info inferred by geophysical means

• 4 regions of Earth's interior

4 regions of Earth's Interior

Crust, Mantle, Inner Core, Outer Core

Crust

• Outermost shell, consists of a broad mixture of rock types

• Depth of 5 km below ocean to near 20 km below land

• Less than 1% of the Earth's volume, 0.4% of Earth's mass

• Moho discontinuity

Mohorovicic discontinuity (Moho)

A relatively narrow zone, that has a significant change in mineral composition

Mantle

• Extends to depth of 2900km (1800 miles)

• Largest of 4 shells

• Makes up 84% of total volume, 67% of total mass

• 3 Sublayers

Mantle's 3 Sublayers

Lithosphere, Asthenosphere, Rigid rocks (lower mantle)

Lithosphere

This uppermost mantle zone together with the overlying oceanic or continental crust

Asthenosphere

Beneath the rigid layer or the lithosphere, and extending to a depth of as much as 350km (200 miles) is a mantle zone in which the rocks are hot enough that they lose much of their strength and become "plastic"- they are easily deformed, somewhat like tar

Outer Core

- Molten, extends to depth of 5000km

Inner Core

• Dense mass with radius of about 1450km

• Primarily made of iron/nickel or iron/silicate

• 2 zones combined make up 15% of the Earth's volume and 32% of the Earth's mass

• Magnetic field of Earth controlled by outer core

• Magnetic poles not the same as the axial poles

Earth's Magnetic Field

• Generated in the outer core

• Convective circulation within the conductive liquid iron and nickel outer core, spiraling in line with Earth's rotational axis, induces the magnetic field of our planet through what is sometimes called a geodynamo

Plate Tectonics and the Structure of Earth

• Plate tectonics is the accepted theory that lithosphere is broken into continent-sized plates floating, slowly moving over hot, soft asthenosphere below

• Driven by convective heat flow within Earth, plates pull apart, collide, and slide past each other

• Linked to faulting, folding, and volcanic activity along boundaries of plates

Minerals

- naturally formed compounds and elements of Earth

Mineral characteristics

• solid

• found in nature

• inorganic

• specific chemical composition

• contains atoms that arrange in pattern to form crystals

The composition of Earth

• Only 8 elements form more than 98% of the mass of Earth's crust

• oxygen and silicon alone make up more than 3/4 of the mass of the crust

• approximately 4400 minerals are identified, with new types identified almost every year

• Only a few dozen rock-forming minerals constitute all crustal rocks

• rock-forming minerals grouped into 7 principal "families" based on chemical properties and internal crystal structure

Important crustal minerals

- Silicates, Oxides, Sulfides, Sulfates, carbonates, Halides, Native elements

Silicates

Combine oxygen and silicon, the most common elements in the lithosphere

Oxides

Elements that are combined with oxygen

Sulfides

Combination of sulfur and another element (pyrite)

Sulfates

Contains sulfur and oxygen

Carbonates

Light-colored minerals that are composed of a combination of carbon, oxygen and an element (limestone)

Halides

Derived from word "salt", salty minerals

Native elements

Gold/silver

Rocks

• Composed of many minerals

• Fewer than 20 minerals make up 95% of the composition of crust rocks

• outcrops, bedrock, regolith

Outcrop

Solid rock that is found rights at the surface

Bedrock

Over most of Earth's land area, through, solid rock exists as a buried layer

Regolith

Bedrock is covered by a layer of broken rock
- Soil, when present, comprises the upper portion

Igneous Rocks

• "fiery inception"

• Magma, lava, pyroclastics

• Classification of igneous rocks is based on mineral composition and texture

• texture based on how rocks cool

Magma

Molten rock beneath Earth's surface

Lava

Molten rock when it flows onto Earth's surface

2 Types of igneous rocks

• Plutonic(intrusive)

• Volcanic(extrusive)

Plutonic(intrusive)

• Rocks cool beneath earth's surface

• Surrounding rocks insulate the magma intrusion, slowing cooling

• Individual minerals in a plutonic rock can grow to large size

• Granite

Volcanic(extrusive)

• Form on Earth's surface

• Cool rapidly

• Generally, do not show individual mineral crystals, but can if the crystals are formed from shattered rock that was explosively ejected

• Basalt

Sedimentary Rocks

• External processes cause rock disintegration

• Material transported by water as sediment

• Over long periods, large amount of sediment build to large thicknesses

• Exert enormous pressure which cause particles in sediment to interlock

• Chemical cementación takes place

• Form sedimentary rock

• Strata

Strata

Horizontal layers of sedimentary rock; sometimes tilted into vertical by Earth processes

2 primary types of sedimentary rocks

• clastic

• chemical and organic sedimentary rocks

Clastic

• Composed of fragments of preexisting rocks

• also known as derrítale rocks

• Shale

• Conglomerate; composed of pebble-sized fragments

Chemical and organic sedimentary rocks

• Formed by precipitation of soluble materials or complicated chemical reactions

• Limestone and coal

• Organic sedimentary rocks such as coal form from remains of dead plants and animals

Metamorphic Rocks

• Rocks which were originally igneous or sedimentary and have been changed by heat and pressure

• Causes a "cooking" of rocks

• Rearrange the crystal structure of the original rock

• Contact metamorphism

• Regional metamorphism

• Hydrothermal metamorphism

• Limestone become marble; sandstone becomes quartzite, shale becomes slate

Contact metamorphism

Occurs beneath Earth's surface where the rocks in contact with magma are altered by heat and pressure
- as a result, it is common to find exposed metamorphic rocks adjacent to plutonic rocks such as granite

Regional metamorphism

Takes place where large volumes of rock deep within the crust are subjected to heat and/or pressure over long periods of time, such as happens in areas of mountain building or in subduction zones, where the edge of one lithospheric plate slides below another plate

Hydrothermal metamorphism

Occurs where hot, mineral-rich-fluids circulate through cracks in rocks

Schist

metamorphic rocks with narrow foliations

Gneiss

Broad, banded foliations

The rock cycle

- processes where rocks can transition from igneous rocks to sedimentary rocks to metamorphic rocks

Continental and ocean floor rocks

• Sedimentary rocks make up 75% of the continents

• Sedimentary cover is not thick

• Continental crust: Sial (silicon and aluminum)

• Ocean floor crust: Sima (silicon and magnesium)

• Ocean lithosphere is more dense than continental lithosphere

• Ocean crust can be subducted into the asthenosphere

Isostasy

• the lithosphere "floats" on the denser, deformable asthenosphere below

• this adjustment of Earth's crust due to the amount of load atop

• added weight on portion of lithosphere cause it to sink, while removal of weight causes it to rise

• Isostatic adjustment has variety of causes

• surface can be depressed from deposit of sediments or amassing of glacial ice on a landmass

• Depressed crust rebounds to higher elevation as material on top erodes, ice sheet melts, or as a large body of water drains

Is oceanic or continental lithosphere denser? Why?

Oceanic lithosphere is more dense than continental lithosphere because Basalt is denser than granite. The Lena floor crust, is composed almost entirely of basalt and gabbro

Topography

Is the surface configuration of Earth and a landform is a topographic feature of any size

Geomorphology

Study of landforms

Basic elements of the landscape

• structure

• the nature, arrangement, and orientation of materials in a landform

• Process

• action that have combined to produce a landform

• Slope

• angular relationship between a surface and surrounding landscape

• Drainage

• movement of water, over surface or down into soil and bedrock

Relief

Is the difference in elevation between highest and lowest point in an area, useful at any scale
- is temporary in landscapes, a momentary balance between opposing processes that shape and reshape the surface

Internal Processes

Originate from within Earth; tend to increase relief of land surface

External Processes

Largely from sources above lithosphere and decrease relief of land surface

Uniformitarianism

Doctrine of uniformitarianism holds the processes that shaped landscape of today are the same the formed topography of the past and will shape the topography of the future

• ongoing process

• do not operate at same rate or same extent in Earth's history

• Change happens episodically and abruptly in "local catastrophes"

• still most processes operate very slowly by human standards

Geologic time

• length of geological time encompasses epochs of millions or hundred of millions of years

• Geologic time refers to vast periods of time over which geologic process operate

Age of Earth

Scientist estimate Earth is nearly 4.6 billion years old

Geologic Time Scale

Geologic time scale is divided into units of time that reflect major events in Earth's history

Scale and pattern

• Regardless objects of study, recognizable features and associations will vary depending on scale of observation

• Horseshoe park, Rocky Mountain, National Park, Colorado

The Pursuit of Pattern

Major landform assemblages of the world

Earth's crust floats on a layer of the mantle called the

Asthenosphere

Silicates combine the most common elements in the lithosphere, which are

Oxygen and silicon

Metamorphic rocks which have defined banding in their foliations are called

Gneiss

The term relief refers to

The distance between the highest and lowest points in a region

A change in a region's perspective depending on the observer's point of view is an example of

The scale of the observation

The largest shell (by volume) in the vertical structure of earth is the

Mantle

The geographer's concern with Earth's interior is restricted primarily to its influence on

Topography

The basic classification of rocks is based on

Origin

Coal is an example of

An organic sedimentary rock

When subjected to metamorphism, limestone usually becomes \________.

marble

The Hydrologic Cycle

• Bulk of Earth's moisture (99%) is in storage in oceans, lakes, rivers, glacial ice, or rocks beneath the surface

• Remaining fraction involved in a continuous sequence of movement and change

Total hydrosphere & % stored in various forms

• Oceans 97.2% (Salt Water)

• Fresh Water 2.8%

• Glaciers 2.15%

• Groundwater 0.62%

• Freshwater lakes 0.009%

• Soil Moisture 0.005%

• Atmosphere 0.001%

• Streams 0.0001%

• Saline lakes 0.008%

3 Primary Movement Types

• Surface to air

• Air to surface

• Movement beneath the surface-runoff

Surface to air

• Ocean evaporation

• Vapor remains in air for a short time

Air to surface

• Precipitation- 78% falls on oceans and 33% on land

• Precipitation is the same as evaporation over long time scales

Movement beneath the surface-runoff

• Water collects in lakes and rivers and either penetrates ground or runs off if sloped

• Becomes part of underground water supply

• Much of the soil moisture eventually evaporated or transpires back into the atmosphere, and much of the underground water eventually reappears at the surface via springs

Moisture Balance of Continents and Oceans

Total of World Surface Area

• Oceans 71%

• Continents 29% Total of World Precipitation Received

• Oceans 78%

• Continents 22% Total of World Water vapor from Surface

• Oceans 86%

• Continents 14%

Residence Times

• Although closed system, residence times for individual molecules of water vary hugely

• may be thousand or millions of year for water store in laical ice or trapped beneath Earth's surface

• Water that is moving in the cycle is in almost continuous movement

Energy Transfer in the Hydrologic Cycle

• System is powered by the sun

• Reservoir or energy, latent heat "stored" in water vapor is released during condensation

• Acting as the fuel for storms

Is the amount of precipitation and evapotranspiration over the continents the same? Explain.

No; more water falls on the continents as precipitation than is added to the air above through evapotranspiration - the "extra" precipitation falling on the continents comes from water evaporated from the oceans.

The Oceans

• vast majority of the surface is oceans

• 5 Principal Parts

• Pacific- largest, occupies 1/3 of total Earth surface area

• Atlantic- less than half the size of the pacific

• Indian- slightly smaller than Atlantic

• Arctic- small and shallow

• Southern- surrounding Antarctica

• Smaller bodies: sea, gulfs, and bays

Characteristics of ocean waters

• Chemical composition

• Sodium and chlorine

• Salinity

• Increasing acidity

• Carbon dioxide absorbed by ocean water creates carbonic acid

• Affects the ability of microscopic creatures to build shells and exoskeletons

• Temperature

• Decreases with increasing latitude

• Ranging from over 80 deg F to near 28 deg F

• Density

• High temp means low density

How and why does the salinity of seawater vary around the world?

Salinity is generally highest in subtropical areas, where evaporation is high. Salinity is generally lowest near the mouths of major rivers; near the equator, where rainfall is high; and in polar areas, where evaporation is low and meltwater from glaciers enters the ocean.

Temperature

• surface seawater temperature decreases with increasing latitude

• Western sides of oceans are warmer than eastern margins due to major warm ocean currents moving poleward

3 primary movement of ocean waters

- tides, currents, and waves

Tides

• Bulges in sea surface in some place that are compensated by sinks in the surface at other places

• Significant in shallow water areas for horizontal placement of water

Causes of Tides

• Gravitational attraction of Moon (lunar tides) and Sun (solar tides)

• More gravitational force on the side of Earth facing the Moon

• 2 bulges form on opposite side of planet

• 2 tidal cycles in 25 hours

• Flood tide and high tide

• Ebb tide and low tide

Monthly tidal cycles

• Tidal range

• Spring tides

• Neap tides

• Global range of tides

Tidal Range

Difference in high and low tides

Currents

• subtropical gyres develops from surface wind patters

• deep ocean circulations

• Global conveyor-belt circulation

Deep Ocean circulations

• Result from differences in salinity and temperature in deep ocean water

• Thermohaline circulation

• Water is northern latitudes is colder and higher salinity, so it sinks

Waves

• Disturbances to the sea surface

• Little forward progress is observes

• Wave breaking can result in shifting of water

Cryosphere

• Second greatest storage of Earth's water

• 2 groups: ice inland and ice in water

• Approximately 10% of Earth's surface is ice covered or frozen

• Largest ice pack covers most of the Arctic Ocean surface

• Several large ice shelves attached to Antarctica

• Large ice floes form off Antarctica

Different names in the Cryosphere

• Ice pack

• Ice shelf

• Ice floe

• Iceberg

Permafrost

• Most ground ice is permafrost: permanently frozen subsoil

• Small proportion of Earth's ice occurs as ground ice

• Occurs only when temperatures are continuously below freezing

• Found widespread in high-latitude continents and in small patches in many high mountain regions

• Mostly ground ice develops as ice crystals form in spaces between soil particles

• Some ground ice is aggregated as veins of frozen water

Thawing of permafrost

• In areas of widespread permafrost, during summer, the soil thaws in the active layer usually only upper 30-100cm (12-14 inches)

• below that is layer permanently frozen ground about 50 m (165 ft)

• Many areas are seeing more than with rising temperatures

• ground temps have risen above melting point of permafrost

• as ground thaws, structure built upon permafrost are destabilized

• poor surface drainage can lead to wet thermokarst conditions

• on coastlines, contributes to more rapid erosion

• thawing leads to increase in microorganisms in soil, causing increased carbon dioxide and methane to be released

Surface Waters

• Represent only 0.02% of the world's total moisture

• Numerous surface water type

Lakes

• bodies of water surrounded by land

• small lakes are called ponds

• Lake Baykal in Siberia is the largest lake by volume

• Saline vs freshwater lakes

• Ephemeral lakes (only contain water sporadically)

• 2 conditions required for lake formation

• Most are relatively short lived

2 conditions required for lake formation

• Natural basin with restricted outlet

• Sufficient water to keep basin filled

Human alteration of natural lakes

• Irrigation

• Water diversion projects

• Reservoirs

• Artificial lakes used for hydroelectric power, municipal water, and stable agriculture