An Introduction to Geology

The Science of Geology Geology - the science that pursues an understanding of planet Earth Physical geology - examines the materials composing Earth and seeks to understand the many processes that operate beneath and upon its surface Historical geology - seeks an understanding of the origin of Earth and its development through time

The Science of Geology Geology, people, and the environment Many important relationships exist between people and the natural environment Problems and issues addressed by geology include Natural hazards, resources, world population growth, and environmental issues

Geologic time Geologists are now able to assign fairly accurate dates to events in Earth history (absolute dating) Relative dating and the geologic time scale Relative dating means that dates are placed in their proper sequence or order without knowing their age in years

The geologic time scale Figure 1.7

Precambrian 4.6 billion years to 544 million years. Represents 88% of all of the history of the earth. Referred to as the Cryptozoic Eon. “hidden life” (no more BIFs) (prokaryotes)

Precambrian: The First 4 Billion Years 88% of geologic time

Geologic time The magnitude of geologic time Involves vast times – millions or billions of years An appreciation for the magnitude of geologic time is important because many processes are very gradual (uniformitarianism) Earth 4.6 Billion Years Old

The nature of scientific inquiry Science assumes the natural world is consistent and predictable Goal of science is to discover patterns in nature and use the knowledge to make predictions Scientists collect data through observation and measurements

The nature of scientific inquiry How or why things happen is explained using a Hypothesis – a tentative (or untested) explanation Theory – a well-tested and widely accepted view that the scientific community agrees best explains certain observable facts Law-a general observation that holds true without explaining why it holds true

The nature of scientific inquiry Scientific method involves Gathering facts through observations (data) Formulation of hypotheses and theories There is no fixed path that scientists follow that leads to scientific knowledge

A view of Earth Earth is a planet that is small and self-contained Earth’s four spheres Hydrosphere Atmosphere Biosphere Solid Earth

Earth’s Spheres ATMOSPHERE Air BIOSPHERE Living Things Atmosphere Contains all the air in Earth’s system. BIOSPHERE Living Things Contains all of Earth’s living things— microorganisms, plants, and animals. Atmosphere LITHOSPHERE Land Contains all the cold, hard, solid land of Earth’s crust (surface), the semi-solid land underneath the crust, and the liquid land near the center. HYDROSPHERE Water Contains all the solid, liquid, and gaseous water of Earth.

What is the Biosphere? All regions of the Earth that are capable of supporting life. Evolved about 3.5 billion years ago 20-30 km thickness (deep ocean trenches into the atmosphere) Includes portions of the hydrosphere, lithosphere, atmosphere, and cryosphere.

The biosphere is the total of all of Earth's ecosystems The global ecosystem is called the biosphere It is the sum of all the Earth's ecosystems The biosphere is the most complex level in ecology Figure 34.2A

The Biosphere We divide the total biosphere into three parts the Atmosphere the Hydrosphere the Lithosphere

The Biosphere It is the physical and chemical parameters of each habitat that selects for the autochthonous community.

The Biosphere The Biosphere (a.k.a. Ecosphere) - the totality of life on earth and the abiotic surroundings that is inhabited. Earth minus sterile areas: strata below the crust upper atmosphere habitats of extreme heat or lacking liquid water

Hydrosphere The earth’s water is found as a LIQUID in rivers, lakes, oceans, rain GAS in our atmosphere SOLID in snow and ice 71% of the earth’s surface is covered by water

Hydrosphere Liquid Gas Solid

Water Distribution

Processes of the Hydrologic Cycle Evaporation - the transformation of water from a solid or liquid to a gaseous state Condensation - transformation of vapor into a liquid Precipitation - liquid or solid water that falls from the atmosphere to the earth’s surface

The Hydrosphere Freshwater Limnetic Habitats (Limnology) 2. Lotic Habitats (running water) a. Springs b. Streams c. Rivers

The Hydrosphere Freshwater - Lake Zonation euphotic zone littoral zone surface limnetic zone (P>R)  profundal zone (P>R)  compensation depth

Oceans

0.5% Groundwater 0.02% Rivers and Lakes

Structure of Atmosphere From Cunningham & Cunningham, 2004, Fig. 9.1

Atmospheric Composition % by Volume Major Constituents Nitrogen 78.1 Oxygen 20.9 Active Minor Constituents Water vapor (H2O) variable (0.48 aver.) Carbon Dioxide (CO2) 0.035 Methane (CH4) 0.00014 Nitrous oxide (NO2) 0.00005 Ozone (O3) 0.000007 CFC’s 0.00000014 H2O (liq & ice) 0.00000002 Inactive Minor Constituents Argon 0.93 Neon 0.0018 Helium 0.00052 Krypton 0.0001 Xenon 0.000009 Hydrogen 0.00005

Other Components of the Atmosphere Water Droplets Ice Crystals Sulfuric Acid Aerosols Volcanic Ash Windblown Dust Sea Salt Human Pollutants

Structure of the Atmosphere Defined by Temperature Profiles Troposphere Where Weather Happens Stratosphere Ozone Layer Mesosphere Thermosphere Ionosphere

Troposphere This is the layer that is closest to the surface of the earth It’s elevation ranges from 0 to 10 km

Stratosphere This layer sits on top of the troposphere It’s elevation ranges from 10 km to around 25 km This layer contains the ozone layer, which protects us from harmful sunlight

Mesosphere This layer is above the stratosphere It’s elevation ranges from 25 to 100 km

Thermosphere This is the highest layer of the atmosphere It’s height ranges from 100 to 400 km This is where most small meteorites burn up and is also the location in the atmosphere that the northern lights occur (aurora borealis)

Why is the Mesosphere so Cold? Stratosphere warmed because of ozone layer Thermosphere warmed by atoms being accelerated by sunlight Mesosphere is sandwiched between two warmer layers

Composition and Altitude Up to about 80 km, atmospheric composition is uniform (troposphere, stratosphere, mesosphere) This zone is called the homosphere Above 80 km light atoms rise This zone is sometimes called the heterosphere

The surrounding air of the Earth Atmosphere The surrounding air of the Earth

Earth as a system Earth is a dynamic planet with many interacting parts or spheres Earth System Science Aims to study Earth as a system composed of numerous interacting parts or subsystems Employs an interdisciplinary approach to solve global environmental problems

Earth as a system The Earth system is powered by the Sun that drives external processes in the Atmosphere Hydrosphere At Earth’s surface The Earth system is also powered by Earth’s interior

Earth as a system What is a system Feedback mechanisms Any size group of interacting parts that form a complex whole Open vs. closed systems Feedback mechanisms Negative feedback – maintains the status quo Positive feedback – enhances or drives changes

Early evolution of Earth Origin of planet Earth Most researchers believe that Earth and the other planets formed at essentially the same time Nebular hypothesis Rotating cloud called the solar nebula Composed of hydrogen and helium Nebula began to contract about 5 billion years ago

Early evolution of Earth Origin of planet Earth Nebular hypothesis Assumes a flat, disk shape with the protosun (pre-Sun) at the center Inner planets begin to form from metallic and rocky substances Larger outer planets began forming from fragments of ices (H2O, CO2, and others)

The Nebular Hypothesis

Early evolution of Earth Formation of Earth’s layered structure Metals sank to the center Molten rock rose to produce a primitive crust Chemical segregation established the three basic divisions of Earth’s interior Primitive atmosphere evolved from gases in Earth’s interior

Early evolution of Earth How did Earth become density stratified?  Young Earth was probably homogeneous  Heat and gravitational pressure caused Earth to partially melt  Gravity then pulled the iron present into the center of Earth  This heated Earth further  Lighter minerals migrated to Earth’s surface and formed the crust  lasted ~100 million years

Earth’s internal structure Layers defined by composition Crust Mantle Core Layers defined by physical properties Lithosphere Asthenosphere Mesosphere Inner and Outer Core

Earth’s layered structure Figure 1.14

Earth Stats Mass (kg) 5.976e+24 Mass (Earth = 1) Equatorial radius (km) 6,378.14 Equatorial radius (Earth = 1) 1.0 Mean density (gm/cm^3) 5.515 Mean distance from the Sun (km) 149,600,000 Mean distance from the Sun (Earth = 1) 1.0000 Rotational period (days) 0.99727 Rotational period (hours) 23.9345 Orbital period (days) 365.256 Mean orbital velocity (km/sec) 29.79 Orbital eccentricity 0.0167 Tilt of axis (degrees) 23.45 Orbital inclination (degrees) 0.000 Equatorial escape velocity (km/sec) 11.18 Equatorial surface gravity (m/sec^2) 9.78 Visual geometric albedo 0.37 Mean surface temperature 15°C Atmospheric pressure (bars) 1.013 Atmospheric composition Nitrogen 77 Oxygen 21 Earth Stats

The face of Earth Earth’s surface Continents Oceans Mountain belts Most prominent feature of continents The stable interior Also called a craton – composed of shields and stable platforms

The face of Earth Ocean basins Continental margins Deep-ocean basins Includes the continental shelf, continental slope, and the continental rise Deep-ocean basins Abyssal plains Oceanic trenches Seamounts

The face of Earth Ocean basins Oceanic ridge system Most prominent topographic feature on Earth Composed of igneous rock that has been fractured and uplifted

End of Chapter 1

Rocks and the rock cycle Basic rock types Igneous rocks Cooling and solidification of magma (molten rock) Examples include granite and basalt Sedimentary rocks Accumulate in layers at Earth’s surface Sediments are derived from weathering of preexisting rocks

Rocks and the rock cycle Basic rock types Sedimentary rocks Examples include sandstone and limestone Metamorphic rocks Formed by “changing” preexisting igneous, sedimentary or other metamorphic rocks Driving forces are increased heat and pressure Examples include gneiss and marble

Rocks and the rock cycle The Rock Cycle: One of Earth’s subsystems The loop that involves the processes by which one rock changes to another Illustrates the various processes and paths as earth materials change both on the surface and inside the Earth

The rock cycle Figure 1.21