DE (W3&4)

• the principle of uniformitarianism is the concept that the same geological processes shaping Earth today have also shaped it in the past.
• Stratigraphy is the study of layering in rocks. These layers are called strata
• Faunal Succession is the theory that different layers contain different fossil assemblage (sets)
• Unconformity is a boundary between two rock layers where rock was never deposited or was eroded before the next layer formed, resulting in a gap in the geological record
• there a many classifications of unconformity including: disconformity, nonconformity and angular unconformity
• disconformity is when an upper sedimentary sequence overlays an erosional surface developed on an undeformed (still horizontal) lower sedimentary sequence
• nonconformity occurs when upper sedimentary beds overlie metamorphic or igneous rock
• angular unconformity occurs when upper sedimentary beds overlay lower beds that have been deformed and then eroded to a more or less even plain
• the geological time scale is a series of intervals, the boundaries of which are based on abrupt changes in the fossil record (fossil sets)
• the largest time scale intervals are Eons: which are further broken down into Eras, periods, epochs and later ages
• many of geological time boundaries are short intervals of mass extinctions where a large percentage of species disappear from the fossil record, and later replaced by new species
• There are four Eons spanning earth's history: Hadean, Archean, Proterozoic and Phanerozic. The last one beginning 542 million years ago when shelly fossils begin to be found
• the principle of uniformitarianism also implies that the Earth must be very old as geologic processes happen slowly
• the principle of original horizontality states that due to gravity, surfaces on which sediments accumulate are fairly flat. Therefore when layers of sediment are deposited they lay horizontally
• the principle of superposition states that each subsequent layer must be younger than the one below of a layer of sediment can not accumulate unless there is already a substrate on which it can collect
• the principle of lateral continuity states that sediment generally accumulates in continuous sheets
• The principle of cross-cutting relationships states that any feature cutting across other features must have formed at a later date.
• the principle of fossil succession states that particular fossil assemblages are only found in limited interval of strata and not above or below that interval.
• index fossils are specific species that are found over a broad region but existed for only a short interval of geologic time
• deep time is the time period of 4.6 billion years since the formation of Earth
• Periods and events can be dated using relative and numerical dating
• relative dating is the sequencing of events or objects by age with respect to one another (oldest to youngest)
• Numerical dating determines the specific date an event occurred, through the use of radioactive decay