Chapter 1: Earth as a Planet
What is Geology?
• Geology
– Scientific study of Earth
• Physical geology
– Understand processes &
materials
• Historical geology
– Sequence of geologic events
Using the scientific method
• Scientific method
– How scientists approach problems
1. Observations & data gathering
2. Formulating hypothesis
•
Hypothesis: plausible, but
not proven, explanation for
how something happens
3. Testing hypothesis
4. Formulating theory
•
Theory: hypothesis tested
& supported by observation
& experimentation
5. Formulating law/ theory
The Earth system
• System concept
– Break large complex items into
smaller pieces without losing sight
of big picture
– Geosphere
• Solid Earth
– Biosphere
• All living & once living organisms
– Atmosphere
• Gasses surrounding Earth
– Hydrosphere
• All water on Earth
– All locations & all states
Cycles and interactions
• Hydrologic cycle
– Describes
movement of water
• Rock cycle
– Processes that form,
modify, transport or
break down rock
• Tectonic cycle
– Processes that drive
movement &
interactions in lithosphere
– Lithosphere
Earth in space
• The solar system
– Earth is about 4.56 billion years old
– Earth is 1of 8 planets orbiting Sun
• Also includes moons, asteroids, comets, meteoroids
– Terrestrial planets
– Jovian
planets
Earth in space
• Differentiation: layering of terrestrial planets based on chemical
composition (i.e. density)
– Crust: outermost
compositional layer
Silicates
• Thin, low-density
& rocky
– Mantle: middle layer
• Rocky, intermediate
density
Solid
Fe/Ni
– Core: innermost layer
• High density &
metallic
Liquid Fe/Ni
Mg; some silicates
& Fe/Ni mixed in
What makes Earth unique?
• Atmosphere
– Rich in oxygen
• Hydrosphere
– Water as solid, liquid
&/or vapor
• Biosphere
– Full of living organisms
• Regolith
– Blanket of loose debris
covering Earth
– Soil
What makes Earth unique?
What makes Earth unique?
• Plate tectonics
– Movement &interactions of large fragments
of Earth’s lithosphere (plates)
– Distribution of volcanoes & earthquakes
• Oceanic crust (basalt)
– Thinner, denser, younger
– Basalt
• Continental crust (granite)
– Older, thicker, less dense
• Uniformitarianism
– Earth processes today operated similarly
throughout geologic history
– “the present is the key to the past”
Why study geology?
• Earth is our home
• Depend on Earth for
resources
• Limited resources
require management
• Earth’s physical &
chemical processes
affect us
• Need to appreciate our own role in geologic change
Chapter 3:
HOW OLD IS OLD?
The Rock Record &Deep Geologic Times
Relative Age
• Sequence of past geologic events
• Age of rock, fossils, or other
geologic feature relative to
another feature
• Stratigraphy
– Study of rock layers & processes that
form them
• Strata
– Rock layers
Relative Age
• Principal of original horizontality: water-laid sediments are
deposited in horizontal layers
Relative Age
• Principle of stratigraphic superposition: each layer is younger
than the layer below it
Relative Age
• Principle of lateral continuity: sediments deposited in continuous
layers
Relative Age
• Principle of cross-cutting
relationship: layer must be
older than any feature that
cuts or disrupts it
Gaps in the record
• Numerical age
– Age of rock or
geological feature in
years before present
• Unconformity
– Substantial gap in
rock sequence;
shows absence of
part of rock record
Fossils and Correlation
• Paleontology
– Study of fossils & record of ancient life on Earth
– Use fossils to determine relative rock ages
• Principle of faunal & floral succession
– Stratigraphic
ordering of fossil
assemblages
• Correlation
• Equate ages of
strata from 2
or more different
places
The
Geologic
Column
• Geologic time
in 1 year
Numerical Age & rates of decay
• Radioactivity
– Process where element
spontaneously transforms
– Radioactive decay
• Parent atoms
• Daughter atoms
• Half life
– Time needed for 50% of parent
atoms to decay into daughter atoms
• Radiometric dating
– Use radioactive isotopes to determine
numerical age of minerals, rocks &
fossils
Rates of decay
• Examine Figure 3.15 and determine the relative age of
rock layer 4
The Age of Earth
• Oldest rock: about 4 billion years
old
– Oldest mineral grain : 4.4 billion
years old
• Meteorites
• Carbonaceous chondrites
– Thought to contain unaltered
material from solar system
formation
– Around 4.56 billion years old
Lab Exercise 2: Maps
Global Positioning System
• Global navigation satellite system for determining location
on Earth’s surface
– Need minimum of 3 satellites “visible” to determine position on
Earth’s surface
Map Scale
• Map Scale: relates map distance to Earth distance
– Verbal Scale: uses words for relationship
• 1 inch equals 16 miles
– Graphic or Bar Scale: line or bar marked off in graduated distances
•
0 is not at far left to allow for more precise measurements
– Fractional Scale: expressed as fraction or ratio
• Example: 1/50,000 or 1:50,000
– 1 unit of measurement on map is equal to 50,000 units of same
measurement on Earth
» 1 foot = 50,000 feet or 1 cm = 50,000 cm
Calculating Distance with Fractional Scales
1.
2.
3.
Measure distance on map to get “measured distance”
Multiply measured distance by fractional scale denominator to get
“ground distance”
Convert “ground distance” to other units
• Example: If you have a map scale of 1:10,000 and a measured
distance of 3.5 inches; complete the
following: _______ feet, _______ miles
– How?
1. 3.5 (10000) = 35000 inches
2. 35000 / 12 (1 foot) = 2916.67 feet
3. 2916.67 / 5280 (feet in a mile) = 0.55 miles
USGS Topographic Maps
• Common scale = 1:24,000
– Called “7.5 minute” quadrangle map
because map covers 7.5 minutes of
both latitude & longitude
• Marginal map data gives important
info:
–
–
–
–
–
Map title
Map location
Latitude & longitude
Map scales
Declination arrows
• True North (N or *)
• Magnetic North (MN)
• Grid North (GN)
– Map Symbols
Contour Lines
• Connect points of equal elevation
• Contour line rules pg. 41 of your lab manual
– Steep slope – contour lines close together
– Gentle slope – contour
lines farther apart
– Contour interval – interval
of change between 2
contour lines
– Index contour – usually
every 5th line is bolder &
labeled with value
• Helps to calculate
contour interval
Contour Map Basics
• Find the elevations of 2 index contours
– Subtract to find elevation change between 2index contours
• Count the number of lines you cross when going from 1 index
contour to the other
– Divide difference in elevation between
2 index contours by # of lines to find
contour interval
• Example:
– What is the contour interval on this
20 ft
map? _____
780 ft
– What is the elevation of Point A? _____
725 ft
– What is the elevation of Point B? _____
A
B
Topographic Profiles
• Shown in “plan view”
– Viewed from above
• Shows elevation change
along a transect (A to B)
• Creates “side view” of the
landscape
Lab
Exercise
1:
Geologic
Time
Index Fossils
• Index fossil: short-lived species tied to specific time period
– ID’ing specific fossils can date rock layers to specific time period
– Can be used to point out missing
rock layers
Tree Rings, Varves, & Coral
• Tree rings
– Used to find tree age & ID conditions tree experienced in its lifetime
• Count tree rings to find tree age
• Wide rings = good conditions
• Narrow rings = poor conditions
• Varves
– Sediment layers that accumulate
annually due to seasonal fluctuations
• Not frozen = sediment accumulation
• Frozen = no sediment accumulation
• Coral
– Correlation between # of daily growth increments & # of days in year
– Used to determine time period that coral grew