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.