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.