CHAPTER 1: INTRODUCTION TO GEOLOGY, p. 1-25.

GEOLOGY - the study of the earth

"The most important factor in the study of the earth is the concept of GEOLOGIC TIME and the antiquity of the Earth."

PHYSICAL GEOLOGY - examines materials composing the earth; includes processes that operate beneath and on the surface.

HISTORICAL GEOLOGY - the study of earth's origin and its development through time; strives to establish a orderly chronological arrangement of the multitude of physical and biological changes that have occurred in the past.

Geology is also an "environmental science:" it is essential for understanding earth processes, and important to understanding both natural and anthropogenic catastrophes.

CATASTROPHISM - earth's history influenced by great catastrophes (influenced by biblical accounts of God's wrath and flood; a popular theory during 17th & 18th Century (prior to methods of systematic scientific inquiry). Beliefs included:

canyons and mountain formed instantaneously.
Anglican Archbishop James Ussher, studied the chronology of births and events of the Bible and concluded that the earth was "created" in 4004 BC.

UNIFORMITARIANISM - The theory that processes we see going on the planet today are responsible for much of the features we see on the planet (past and present). First publicly promoted by James Hutton, a Scottish geologist (1729-1797) - Summary of Hutton's idea: "The present is the key to the past." Uniformitarianism suggests that slow processes, over great periods of TIME, can account for most of the great features on the planet's surface. Examples include:

earthquakes (x time) = mountains
stream erosion (x time) = canyons
snow (and climate change) (x time) = glaciers
gentle creep of continents across the Earth's surface (x time) = oceans
sand and mud from a river washing onto a coastline (x time) = delta
slow flow of lava on Hawaii = largest mountain (volcano) on earth

Uniformitarianism illustrates that most geologic processes are too slow to be witnessed by human lives. (An example: sea level is currently rising at about 2mm per year.) However, some processes do occur rapidly (catastrophically), examples include asteroid impacts, major floods, landslides, massive earthquakes, and volcanic eruptions. Modern theory incorporates both theories.

EVOLUTION - The theory that over a great period of TIME life has evolved from simple microscopic life forms to modern complex life forms by the processes of genetic mutation and "natural selection." (Charles Darwin wrote "Origin of Species by Natural Selection" in 1859.)

GEOLOGIC TIME - current estimates is that earth "formed" around 4.6 billion years ago; the oldest rocks found on the surface are about 3.8 billion (old rocks crop out on coast of Greenland, core of Wind River Mountains in Wyoming, Australia, Africa).

GEOLOGIC TIME SCALE [p. 8] - Names provided by geologists who studied fossil-bearing rock sequences in many areas around the world.

STRUCTURE OF THE EARTH

INNER CORE - iron, solid, ~1200 km radius
OUTER CORE - liquid metallic iron, ~2300 km thick
MANTLE - dense rock, ~2900 km thick
CRUST - "skin" of light rock, 5-40 km thick.
AESTHENOSPHERE - hot weak zone 100-700 km below, capable of flow.
LITHOSPHERE - cooler, ridged rock upper mantle and crust
HYDROSPHERE - oceans, lakes, rivers, glaciers
ATMOSPHERE - air up to the vacuum of space
BIOSPHERE - includes all life of earth within the earth, water, and air

THEORY OF PLATE TECTONICS - "first proposed as continental drift"

The LITHOSPHERE consists of rigid PLATES floating on a dense, viscous AESTHENOSPHERE. Heat driving plate motion comes from earth formation, radiation, unknown sources.

PLATE TECTONICS works like a "boiling pot with scum" - hot rock rises, cooler denser rock sinks. Within the mantle hot areas are rising beneath ocean ridges, cooler rocks are sinking beneath plate convergent zones (such as around the edges of the Pacific Ocean. The sinking rock around the edge of the continents are full of water and trapped gas that cause some of the rock to melt as it sinks. This molten rock rises to the surface and erupts as volcanos along the sinking plate boundaries. (This process give the Pacific Rim its name "The Ring of Fire.")

PLATES consist of rocks of differing densities:

Oceanic crust - density = 3.5 g/cm3

Continental crust - density = 2.7 g/cm3

The tectonic processes that affect the Earth's surface are most active along the margins of PLATES. There are three types of plate boundaries:

DIVERGENT BOUNDARIES - where plates move apart and hot mantle rocks are rising. When the hot rock reaches the surface it looses pressure and melts (forming very HOT lava). The plates move apart slowly. The process affecting the CRUST is called SEA FLOOR SPREADING. For example, the Atlantic Ocean is spreading apart along the Mid Atlantic Ridge at a rate of about 5cm per year.
CONVERGENT BOUNDARIES - where plate collide mountains form, such as the Himalayan Mountains. If denser ocean crust collides with lighter continental crust the ocean crust sinks beneath the continental crust and partially melts forming volcanos along the continental plate margin. Examples include the Andes, the Cascade Mountains in the US, the island arcs of the Aleutians, Japan, Philippines, and Malaysia. Where one plate over-rides another a deep ocean trench forms adjacent to a coastal volcanic mountain range. This large feature is called a SUBDUCTION ZONE.
TRANSFORM BOUNDARIES - where plates move past one-another, causing major earthquakes: Examples include San Andreas Fault and faults in the valley of the Dead Sea, Jordan, Israel, and Egypt.

THE ROCK CYCLE

The ROCK CYCLE represents a flow chart showing natural processes and earth products.

Important concepts of the rock cycle include:

IGNEOUS ROCK - forms from the solidification of molten rock
MAGMA - molten rock underground
LAVA - molten rock on the surface.
CRYSTALLIZATION - the process of cooling and solidifying magma.
WEATHERING - processes that break down rocks (chemical or mechanical)
SEDIMENT - rock particles or precipitates deposited
LITHIFICATION - processes that bind sediment into rock
SEDIMENTARY ROCK - rock consisting of cemented sediments.
METAMORPHIC ROCK - great heat and pressure physically and chemically change the rock.

RENEWABLE vs. NONRENEWABLE RESOURCES

Mining depletes resources through time. The Earth's crust only has a limited supply of resources - a great concern for the future of the world's growing population...

Non-renewable resources include: coal, oil, gas, minerals, metals, and soil. Renewable resources include: wood, wind, water, oxygen, land

Click here to return to the Class Website