Geological+History

It is estimated that the earth formed along with the solar system 4/6 billion years ago ( 4,600,000 )

Geologic time scale A summery of major events in earths history era Period Epoch ( smallest segment of geologic time)

Reading the rock record relative time vs. Rock Record Relative time Absolute time identifies the actual dates Places, events in a Sequence of geologic events. But does not identify their actual date of occurrence.

-Examples A list in Chronological order of what The exact times at which you did these things you have done today up until his time

Finding the age of rocks with relative time. Law of super position in undisturbed sedimentary rocks the oldest rock layers are the bottom and the youngest are at the top. Law of cross- cutting relationships- An igneous intrusion is younger than the rock it has intrudet into ( look at the whiskers)

Law of included fragments- If fragments of one type of rock are found in another rock layer the rock fragments must be older than the rock layer in which they are found Faulted and folded layers- Layers of rock that have been faulted or folded must have been present before the actions or faulting or folding took place. Unconformity- A place in the rock record where layered of rock are missing because of uplift and erosion. the result can be a large age difference between the rocks above and those below the erosional surface (it appears like a squiggly line in a cross-section) Rock Correlation Matching of rock layers that can be seen at the earths surface, over a large area An outcrop is exposed rock layers at the earth's surface. A key bed is a thin, widespread layer, usually of volcanic ash, that can be used to correlate an exact point of time. Fossils A fossil is any evidence of earlier life preserved in the rock Original Remains(rare)- The actual unchanged remains of the plant or animal are preserved. Replaced remains- The soft parts of the original animal have disappeared and the hard parts have been replaced by mineral material.( petrified wood) Molds and casts- Fossil shells or bones are dissolved completely out of the rock leaving a hollow depression in the rock. New mineral material fills the mold it forms a cast of the original fossil. Trace fossils- Evidence of life which other then remains, which includes any impressions left in the rock.(Trials, Footprints,tracks,burrows) Index Fossil- Easily identifiable Short-Lived Widespread occurrence Measuring Absolute time