Introduction

To Physical Geology

The Science

• Geology is typically broken up into two fields of study

– Physical Geology

– Historical Geology

Physical Geology

• Examines the materials composing Earth and seeks to understand the processes that operate beneath the surface

– It is the how and why of Geology

Historical Geology

• Seeks an understanding of the origin of Earth and its development through time.

– It is the who, what, where, and when

The rock cycle

The rock cycle

- Series of processes by which rocks changes into other types of rocks

- Illustrates various processes and paths as earth materials change both on the surface and inside the Earth

- What are the three main rocks ? 1 -Igneous

2 -Metamorphic 3 -Sedimentary

The rock cycle

Fundamental Rock Types

- Igneous Rocks: solidify from melt, e.g. lava (extrusive) or magma (intrusive)

- Sedimentary Rocks: are made at the Earth’s surface from particle and chemical remnants of other rocks

- Metamorphic rocks: form when other rocks are heated, squeezed, and deformed.

Granite (igneous, intrusive)

Basalt (igneous, extrusive)

Conglomerate (sedimentary)

Shale and sandstone (sedimentary)

Limestone (sedimentary)

Sandstone (sedimentary)

Marble (metamorphic)

Quartzite (metamorphic)

Gneiss (metamorphic)

Earth as a System

– Earth’s Four Spheres• Atmosphere

– The air we breathe

• Hydrosphere– The water we drink

• Biosphere– life

• Solid Earth– Where we live

All of these spheres interact with each other. A minor adjusting In the properties of one could lead to drastic changes in the Properties of the other three

Earth’s Outermost Layers

• The most dynamic portion of the Earth– Atmosphere

• Thin gaseous envelope surrounding Earth– Hydrosphere

• Water layer dominated by the oceans– Biosphere

• All living things on the planet– Lithosphere

• Rocky outer shell

The Atmosphere

•Composition is unique in solar system

–78% nitrogen

–21% oxygen (not present in early

atmosphere)

–Minor amounts of carbon dioxide, argon and water vapor

The Hydrosphere

• Total mass of water on or near the Earth’s surface– Covers 71% of Earth’s surface

– ~98% in oceans

– 2% in glaciers, groundwater, lakes and streams (fresh water)

The Biosphere

• All life on Earth– Animals & plants on land, in the sea

and air

– Microorganisms-the most common form of life

– Evolved within narrow zone near the Earth’s surface

Earth’s Internal Structure

• Solid Earth has a layered structure– Layers defined by composition and

physical properties

– Compositional layers• crust - mantle - core

– Physical layers• lithosphere - asthenosphere -

mesosphere - outer core - inner core

Compositional Layers

• Crust– Outermost compositional layer

– Definite change in composition at the base of the crust

– 2 types:• Continental crust• Oceanic crust

Compositional Layers

• Mantle– Largest layer in the Earth

• 2900 km thick• 82% by volume• 68% by mass

– Composed of silicate rocks with abundant iron and magnesium• Density ranges from 3.2 to 5 g/cm3

Compositional Layers

• Core– Central mass about 7000km in

diameter

– Average density of 10.8 g/cm3

– 16% by volume, 32% of mass

– Indirect evidence of composition• Metallic iron

Physical Layers

• Lithosphere– Crust + upper portion of the mantle

– Solid & rigid

– Thickness ranges from 10 km beneath oceans to 300 km in continental areas

• Crust– Continental crust

• Thick - up to 75 km• Lower density - 2.7 g/cm3

• Strongly deformed• Much older - may be billions of years old

• Crust– Oceanic crust

• Thinner - about 8 km• More dense - 3.0 g/cm3

• Comparatively undeformed• Much younger - < 200 million years old

Physical Geology

• Earth’s Systems– Atmosphere

• gases that surround the Earth

– Hydrosphere• water on or near Earth’s surface

– Biosphere• all living or once-living materials

– Geosphere• solid, rocky Earth

Earth’s Interior

• Compositional Layers– Crust

• Very thin outer rocky shell of Earth

• Variable thickness

– Mantle • Hot solid • Special “plastic” zone• Fe-, Mg-, Si-rich minerals

– Core • Outer core

– liquid – mostly iron

• Inner core – solid– mostly iron

Earth’s internal layers

The Earth in Space

Age of the Earth = 4.5 Billion years[4,600,000,000 years]

Age of the Universe = 14 Billion years

Earth Compared to Other Planets

• The Solar System– The inner planets

• Rocky planets near the Sun• Mercury, Venus, Earth & Mars

– The outer planets• Giant gaseous planets• Jupiter, Saturn, Uranus, Neptune

– Pluto, a small icy minor planet

Origin of the Solar System

• Gravitational collapse of gas & dust cloud [nebula]– Rotation around a central mass

– Disk shaped cloud

– Temperature variations segregated matter

– Small particles accreted into larger planetesimals, planets

How do we Know this?

• Differences between inner and outer planets:– Density – The rocky inner planets=densities of 3 g/cm3 more

– The gaseous outer Planets=densities of 1.6 g/cm3 or less