Transcript Ch 12 and 13 ppt 2010

Ch. 12 and 13
 Rocks record
geological events
and changing
life forms of the
past
 James Ussher (mid 1600’s)
 Constructed a time line of
human and Earth’s history
 Landscape is developed by
catastrophes
 James Hutton – Father of
modern Geology (late
1700’s)
 Published his theories in his book
Theory of the Earth
 Created the fundamental
principle of uniformitarianism
 The focus and process that we
observe today have been at work
for a very long time
 “the present is the key to the past”
 Relative
 Tells us the
sequence in
which events
occurred, not
how long ago
they occurred
 Law of Superposition
(James Hutton’s law)
 In a uniform sequence of
sedimentary rocks, each
bed is older than the one
above it and younger than
the one below it
 This law is used to
determine the age of the
rocks in relative terms.
 Principle of Original Horizontality
 Sediments are generally deposited in a horizontal
position
 Principle of Cross Cutting Relationships
 When a fault cuts through or when magma intrudes
other rocks and crystallizes, the fault or intrusion is
younger than the rock affected
 Inclusions
 Pieces of one rock
unit that are
contained within
another
 Unconformity
 Represents a long period
during which deposition
stopped, erosion
removed previously
formed rocks, and then
deposition resumed
 Gaps missing in the
layers of the earth
 Types of
Unconformities
 Angular: during the pause
in deposition, a period of
deformation (tilting) and
erosion occurred
 Disconformity: two
sedimentary rock layers that
are separated by an erosional
surface
 Nonconformity:
erosional surface separates
older metamorphic or igneous
rocks from younger
sedimentary rocks
 Correlation: matching up
rocks of similar age in different
regions
 Good for matching rocks in
short distances
 Fossils needed for correlation in
great distances
 Remains or traces of
prehistoric life (hard
parts like shells or
bones)
 Found in sedimentary
rocks
 Usually around 10,000
years old for the process
to occur.
 The creature needs to
have possession of hard
parts and rapidly buried
 Petrified: Mineral rich
water soaks into the
small cavities and pores
of the organism turning
it into stone
 Replacement: solid
material of an organism
is replaced by mineral
matter
 Mold : created when a
shell or other structure is
buried in sediment and
dissolved by underground
water (only reflect shape
and surface marking)
 Cast: created if the hollow
spaces of a mold are filled
with mineral matter
(information about
internal structure)
 Impression or
Imprint: pressure
on organism leaves
a picture of the
animals
(like
leaves)
 Amber: Hardened
resin of ancient tree
(good for insects)
 Tracks: animal footprints
made in soft sediment that
was later compacted and
cemented
 Burrows: Holes made by an
animal in sediment, wood, or
rock that were filled with
mineral matter and
preserved
 Coprolites: fossils of dung
and stomach content
 Gastroliths: highly polished
stomach stones that were used
in grinding of food by some
extinct reptile
 Principle of Fossil Succession:
Fossil organisms succeed one another
in a definite and determinable order
 Any time period can be recognized by
its fossil content
 William Smith – proposed this idea in
the late 1700’s and early 1800’s
 Correlations use index fossils
 Index Fossils: widespread
geographically, are limited to a
short span of geologic time and
occur in large numbers
 The most famous index fossil is the
trilobite (600 MY to 400 MY)
 Fossils can also be used to interpret
and describe ancient environments
 Radioactivity: when the nuclei of an atom is unstable and
spontaneously breaks apart or decays
 Continues until a stable or non-radioactive isotope is formed
Half-life
 the amount of time it takes for one half of the nuclei in a sample
to decay to its stable isotope
 Way of expressing the rate of radioactive decay
 Radiometric Dating: A way to calculate the age of rocks and
minerals that contain certain radioactive isotopes (Example:
Uranium – 238)
 Dating with Carbon – 14
 To date recent events
 Uses the element carbon
 Called radiocarbon dating
 Half-life of 5730 years
 The earth is 4.6
Billion Years
Old
The structure of
the Time Scale
 The geologic time
scale is divided
into eons, eras,
periods, and
epochs
 Eons: Greatest expanses of
time
 4 main eons: Hadean,
Archean, Proterozoic, and
Phanerozoic
 Eras: divisions of eons
 Periods: divisions of eras
 Epochs: divisions of
periods
 Precambrian – Longest
era (4 billion years)
 88% of the Earth’s history
 History not known in great
details
 The life forms are often more
difficult to identify and the rocks
have been disturbed often
 The most common fossils are
stromatolites, blue and green
algae
 Paleozoic –
Water World
 Life in the early
Paleozoic time was
restricted to the seas
 Trilobites existed
during this time
 Supercontinent
Pangaea was formed
in the late Paleozoic
era
 Mesozoic – Age of the
Reptiles
 Pangaea breaks up
 Dinosaurs ruled the land, sky,
and seas
 At the end of the Mesozoic era,
many reptile groups became
extinct
 Cenozoic – Age of
Mammals
 Mammals replace reptiles as
the dominant land animals
 Oldest human found was LUCY .
She is 3.4 million years old.
 Evolution - Change in species over
time.
 Environment
 Gene pool depleting
 Mutations
 Adaptations – an organism will change
to increase its chances of survival
 Biodiversity – When there is a genetic,
species and ecological change in an
organism in a given area.
 When the environment will
affect the genetic make up of
an organism and cause
severe changes in the
organism.
 Mountains of NC –
salamanders – acid rain
causes mutations in the
limbs and texture of the
skin.