Presentation on theme: "29.2 R ELATIVE T IME. P AST M ISCONCEPTIONS Before the 1700’s, scientist thought the Earth was ~ 6000 y.o. Given geologic processes take much longer to."— Presentation transcript:
P AST M ISCONCEPTIONS Before the 1700’s, scientist thought the Earth was ~ 6000 y.o. Given geologic processes take much longer to take shape they were able to get a beter idea of how old Earth was.
R ELATIVE D ATING What is relative dating? Relative Dating – The process of placing events in the sequence in which they occurred. Does not give exact dates, just ballpark figures.
R ELATIVE D ATING The Principle of Superposition Remember the Law of Superposition? Explain. Youngest Top, Oldest bottom Intrusions can be youngest depending on their penetration. Embedded fragments are older than the rock that surrounds it. (ex. A pebble in conglomerate is older than the conglomerate itself.)
G APS IN R ELATIVE T IME Unconformity Indicates whether layers of rock are missing from strata (rock layers) sequence.
G APS IN R ELATIVE T IME Unconformity Angular unconformity Strata is tilted during uplift then young flat strata is then deposited over older tilted strata.
G APS IN R ELATIVE T IME Disconformity When layers are eroded away and younger layers replace them causing gaps in the time sequence. (Optional writing) Ex. Layers in a sequence is eroded then covered by a body of water. The sediments in the water settle to form new layers. Although there is a sequence, some of the “pages” are missing.
G APS IN R ELATIVE T IME Nonconformity When sediments are deposited on top of uplifted, eroded igneous rock.
R OCK L AYER C ORRELATION Can you define correlation? Matching of rock layers from one area to another.
R OCK L AYER C ORRELATION Walking the Outcrop An outcrop is a part of the rock layer that can be seen at Earth’s surface. Compare visible rock of one area to another Can be difficult in areas of high vegetation and dense soil.
R OCK L AYER C ORRELATION Matching Rock Characteristics Simply compares rock characteristics such as color, appearance and composition
R OCK L AYER C ORRELATION Using Index Fossils Index fossils are organisms that died during a certain time period. Fossils in one layer of sediment will be different (age wise) than one in another layer of sediment. Four characteristics of index fossils Unique (Easily Identifiable) Abundant Widespread Existed for only a brief period
R OCK L AYER C ORRELATION Fossils as environmental indicators Can indicate an areas past climate. (Optional) Ex. Coral only forms in shallow, warm water b/t 30 N and 30 S. Coral discovered in an area that doesn’t normally have coral would indicate that an area would have been covered by warm, shallow water.
R OCK L AYER C ORRELATION Matching Key Beds Key beds are like index fossils Have to be unique Widespread Easily recognizable Ex. Volcanic eruptions spread across great distance
S TRATIGRAPHIC M ATCHING This is simply matching multiple layers within a strata.