Population Growth

Our Number One Environmental and Resource Problem

Growth Rate and Doubling Time

• Exponential growth– Growth rate, G, measured as a percentage– Doubling time,

D=70/G

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Sustainability

• Development that ensures that future generations will have equal access to the resources of our planet

The Evolving Earth, Geologic Time and Minerals

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A view of Earth

• Earth is a planet that is small and self-contained

• Earth’s four spheres• Hydrosphere• Atmosphere• Biosphere• Solid Earth

Earth as a system

• Earth is a dynamic planet with many interacting parts or spheres

• Parts of the Earth system are linked • Characterized by processes that

• Vary on spatial scales from fractions of millimeter to thousands of kilometers

• Have time scales that range from milliseconds to billions of years

Earth as a system

• The Earth system is powered by the Sun that drives external processes in the

• Atmosphere• Hydrosphere• At Earth’s surface

Earth’s internal structure

• Earth’s internal layers can be defined by • Chemical composition• Physical properties

• Layers defined by composition• Crust• Mantle• Core

Earth’s internal structure

• Four main layers of Earth are based on physical properties and hence mechanical strength

• Lithosphere• Asthenosphere• Mesosphere• Core

Earth’s internal structure

Discovering Earth’s composition

• Two types of crust• Continental crust

– Lighter– Granitic rocks

• Oceanic crust– Denser – Composed primarily of basalt

Discovering Earth’s composition

• Mantle• Solid, rocky layer• Composed of rocks like peridotite

• Core• Thought to mainly dense iron and

nickel• Two parts

– Outer core - liquid – Inner core - solid

Dynamic Earth

• The theory of plate tectonics• Involves understanding the workings of our

dynamic planet• Began in the early part of the twentieth

century with a proposal called continental drift – the idea that continents moved about the face of the planet

Dynamic Earth

• The theory of plate tectonics• A theory, called plate tectonics, has now

emerged that provides geologists with the first comprehensive model of Earth’s internal workings

• Plate boundaries• All major interactions among individual

plates occurs along their boundaries

Distribution of magnitude 5 or greater earthquakes, 1980 - 1990

Dynamic Earth

• Plate boundaries• Divergent boundary – two plates move

apart, resulting in upwelling of material from the mantle to create new seafloor

• Convergent boundary – two plates move together with subduction of oceanic plates or collision of two continental plates

Dynamic Earth

• Plate boundaries• Transform boundaries - located where

plates grind past each other without either generating new lithosphere or consuming old lithosphere

• Changing boundaries - new plate boundaries are created in response to changes in the forces acting on the lithosphere

Divergent boundaries are located mainly along oceanic ridges

The East African rift – a divergent boundary on land

An oceanic-continental convergent plate boundary

An oceanic-oceanic convergent plate boundary

Earthquake foci in the vicinity of the Japan trench

A continental-continental convergent plate boundary

The collision of India and Asia produced the Himalayas

Testing the plate tectonics model

• Hot spots• Caused by rising plumes of mantle

material• Volcanoes can form over them (Hawaiian

Island chain)• Most mantle plumes are long-lived

structures and at least some originate at great depth, perhaps at the mantle-core boundary

The Hawaiian Islands have formed over a stationary hot spot

The driving mechanism• No one driving mechanism accounts for

all major facets of plate tectonics • Researchers agree that convective flow in

the rocky 2,900 kilometer-thick mantle is the basic driving force of plate tectonics

• Several mechanisms generate forces that contribute to plate motion

• Slab-pull• Ridge-push

The driving mechanism

• Models of plate-mantle convection • Any model describing mantle convection

must explain why basalts that erupt along the oceanic ridge

• Models– Layering at 660 kilometers– Whole-mantle convection– Deep-layer model

Minerals: Building blocks of rocks

• Definition of a mineral:• Naturally occurring• Inorganic solid• Ordered internal molecular structure• Definite chemical composition

• Definition of a rock:• A solid aggregate or mass of minerals

Structure of minerals

• Minerals consist of an orderly array of atoms chemically bonded to form a particular crystalline structure

• For ionic compounds, the internal atomic arrangement is primarily determined by the size of ions involved

Composition of minerals

• Elements• Basic building blocks of minerals• Over 100 are known (92 naturally occurring)

• Atoms• Smallest particles of matter• Retains all the characteristics of an element

The periodic table

Classification of Minerals• Nearly 4000 minerals have been identi-

fied on Earth• Rock-forming minerals

• Common minerals that make up most of the rocks of Earth’s crust

• Only a few dozen members• Composed mainly of the 8 elements that

make up over 98% of the continental crust

Classification of Minerals• Silicates

• Most important mineral group– Comprise most of the rock-forming minerals– Very abundant due to large amounts of

silicon and oxygen in Earth’s crust• Basic building block is the silicon-

oxygen tetrahedron molecule– Four oxygen ions surrounding a much

smaller silicon ion

The silicate (SiO4)-4

molecule

Silicate structures

Classification of Minerals

• Important nonsilicate minerals• Several major groups exist including

– Oxides– Sulfides– Sulfates– Native Elements– Carbonates– Halides– Phosphates

Mineral Resources• The endowment of useful minerals

ultimately available commercially• Metals and Nonmetals• Mineral resources include

– Reserves – already identified deposits– Known deposits that are not yet

economically or technologically recoverable

Mineral Resources

• Ore– A useful metallic mineral that can be

mined at a profit– Must be concentrated above its average

crustal abundance– Profitability may change because of

economic changes

Minerals and the Environment

• Most minerals are only metastable• Reactive to air and water• Can contribute significant concentrations

to soil and water• May have impact on human health

The rock cycle