Ch. 12 and 13. Rocks record geological events and changing life forms of the past.
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Transcript of Ch. 12 and 13. Rocks record geological events and changing life forms of the past.
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 historyLandscape is developed by
catastrophes
James Hutton – Father of modern Geology (late 1700’s)Published his theories in his
book Theory of the EarthCreated 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”
RelativeTells 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 HorizontalitySediments are generally deposited in a
horizontal position
Principle of Cross Cutting RelationshipsWhen 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
UnconformityRepresents 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 UnconformitiesAngular: 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 orderAny time period can be
recognized by its fossil contentWilliam Smith – proposed this
idea in the late 1700’s and early 1800’s
Correlations use index fossilsIndex 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 decaysContinues until a stable or non-radioactive isotope is
formed
Half-lifethe amount of time it takes for one half of the nuclei in
a sample to decay to its stable isotopeWay of expressing the rate of radioactive decayRadiometric Dating: A way to calculate the age of
rocks and minerals that contain certain radioactive isotopes (Example: Uranium – 238)
Dating with Carbon – 14To date recent eventsUses the element carbonCalled radiocarbon datingHalf-life of 5730 years
The earth is 4.6 Billion Years Old
The structure of the Time ScaleThe geologic time scale is divided into eons, eras, periods, and epochs
Eons: Greatest expanses of time4 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
detailsThe 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 WorldLife 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 ReptilesPangaea breaks up Dinosaurs ruled the land,
sky, and seasAt the end of the Mesozoic
era, many reptile groups became extinct
Cenozoic – Age of MammalsMammals 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.