Chapter 2 – Earth Systems: Processes and Interactions
2.1 The Solid Earth System: Components and Processes
 Earth’s interior consists of crust, mantle and core; the crust and the uppermost
mantle together constitute the lithosphere
o The lithosphere consists of a series of plates that move over the underlying
asthenosphere in the process of seafloor spreading
o Convection cells bring hot mantle rock upward beneath mid-ocean ridges,
(long submarine volcanic mountain ranges), pushing plates apart to form
new ocean crust between them
o Ocean crust is destroyed by subduction in seafloor trenches; magma is
produced by this process, feeding another type of volcano
o Magma plumes originate deep in the mantle and may initiate a cycle of
rifting followed by the collision of continents, which causes mountain
building (orogeny); this is known as the tectonic cycle
2.2 Rock Cycle
 The rock cycle involves the formation and destruction of the three major rock
types (lithologies): igneous, sedimentary and metamorphic
 Igneous Rocks
o Cooled and solidified from magma
o Granite (or granitic rocks) comprises the continents whereas basalt forms
the ocean floor
o Intrusive igneous rocks form beneath Earth’s surface; extrusive igneous
rocks form in association with volcanic activity
o Magmas of different composition form as a result of partial melting
processes in various plate tectonic settings
 Sedimentary Rocks
o Form at Earth’s surface from the products of physical and chemical
weathering
o Are typically layered (stratified)
o Deposited as loose grains (“sediment”), may undergo lithification for form
sedimentary rock
o Frequently contain fossils (remains of preexisting organisms)
 Metamorphic Rocks
o Formed by heat and pressure that physically and chemically transform
other rocks into metamorphic rocks
o The heat involved in metamorphism is not sufficient to completely melt
the rock
o Metamorphism is frequently associated with intense conditions generated
during mountain building
o Can also occur in or adjacent to subduction zones, in rocks adjacent to
magma, during burial, by injection of hot fluids into rock, or where large
extraterrestrial bodies impact the Earth
2.3 Atmosphere and Its Circulation
 The atmosphere comprises the gaseous envelope surrounding Earth (about 200
km thick)
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o Helps warm Earth through greenhouse effect; also shields planet from
cosmic radiation
o The modern atmosphere is mainly composed of nitrogen (78%) and
oxygen (21%); carbon dioxide comprises only a trace amount (0.038%)
o Carbon dioxide and water vapor both contribute to warming the Earth
 Atmospheric circulation is driven by the temperature contrast between the equator
and poles
o This contrast results from different fluxes of solar radiation reaching
Earth’s surface
o The atmosphere attempts to “smooth out” this temperature gradient by
transferring heat from the equator toward the poles by convection
o Earth’s wind patterns result from the effects of atmospheric convection
combined with Coriolis effect (due to Earth’s rotation)
2.4 The Hydrosphere
 Hydrologic Cycle – involves the flux of water through several reservoirs
o Precipitation may be lost through evaporation, may flow on Earth’s
surface as runoff (until reaching the oceans), or may infiltrate the ground
(and become groundwater)
o Water is used by plants (part of the biosphere), which lose large amounts
through their leaves (transpiration)
o Ice may be described as a separate Earth system from the hydrosphere, the
cryosphere
 Ocean Circulation – the oceans are the dominant component of the hydrosphere
o Oceans cover 70% of Earth’s surface and average 3.8 km in depth
o They store 96.5% of Earth’s water, account for over 86% of all
evaporation, and receive 78% of all precipitation
o Water’s high heat capacity makes the ocean the largest reservoir and
regulator of heat on Earth, and therefore a major influence on climate
o Earth’s wind systems drive the major surface currents (gyres) under the
influence of Coriolis effect
o The deep water masses circulate somewhat more slowly in the “oceanic
conveyor” (meridional ocean circulation)
o Density differences between water masses (due to temperature and
salinity) play a role in their movement
o Oceans also affect Earth’s albedo (surface reflectivity) because they are
dark and thus radiate solar energy as heat
2.5 The Biosphere
 Biogeography: Distribution of Plants and Animals Over Earth’s Surface
o The biosphere consists of the total living biota (organisms) of Earth
o Organisms are not uniformly distributed; instead, each type (species) has a
certain range of physical environmental factors within which it can live
and reproduce
o This tolerance to environmental factors determines the biogeographic
distribution of different species
o On land, regions are characterized by biomes; in the ocean, various
provinces are distinguished
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o Each continent or ocean basin tends to have its own distinctive biota
(species of plants or animals)
Energy Relationships
o The populations of different species living within an area are organized
into communities
o Communities, along with their surrounding physical environment,
comprise ecosystems (open systems maintained by the flow of energy and
matter)
o The niche of a species refers to its role or function within an ecosystem,
defined primarily by its trophic (feeding) relationships
o A food pyramid shows how food (energy) is passed from one trophic level
to another in a community; generally, such transfers are only about 10%
efficient in converting energy to biomass
Biogeochemical Cycles – cycles of various chemical elements through the
biosphere on different time scales
o Involve the interplay of several of Earth’s major systems
o The recycling of nutrients helps sustain ecosystems; ecosystems,
communities, and the biosphere in general are typically nutrient limited
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Chapter 2: Earth Systems: Processes and Interactions