PPT-Geologic Time Dating There are two basic approaches: relative age dating, and absolute

Relative Dating To determine the relative age of different rocks geologists start with the assumption that unless something has happened in a sequence of sedimentary rock layers the newer rock layers will be on top of older ones This is called the Rule of Superposition. 01: . Geologic Time . Scale. Huge sections of time are broken down into smaller groups of time:. E. ons, Eras, . P. eriods, and . E. pochs. Eon. is the largest time block. . (kind of like what we would think of as years).. How long ago were the dinosaurs here? How do we even describe geologic time anyway?. EONS. which are divided into . ERAS. ,. which are divided into. . PERIODS. ,. which are divided into. . EPOCHS. Dating. Methods. archaeological . dating methods. relative . dating . (aka “older/younger” dating). chronometric dating. . (. aka “absolute” dating). Relative and Chronometric Dating. In depth: chapter 19. Geologic Time Scale. Examining layers of sedimentary rock, scientists have put together a chronology of Earth’s history.. It is divided into 4 Eras:. 1. Precambrian (3.5 . bya. 8. th. Grade Science. Geologic Time. Geologic time. . - Earth’s history is divided into units of time that make up the . Geologic . T. ime . S. cale. .. Time units on the scale are based on the appearance (. East-Central Idaho — . Metasedimentary. Strata, . Ore . Types, . Folds, Dikes, and Metamorphic Overprint. Art . Bookstrom. , Steve Box, Pam Cossette, . Tom Frost, and Shane . Kostka. . Regional Geologic Map showing the Mesoproterozoic Belt-Purcell basin and the Lemhi sub-basin . The geologic time scale divides Earth’s long history into units of time…. Eras. .  . Periods. .  . Epochs. Eras. are divided into . P. eriods. .. Periods. are divided into . Epochs. .. Precambrian. Mrs. Wright. 8. th. Grade Science. Bath County Middle School. Superposition. —Oldest Rocks on the Bottom. According to the . principle of superposition. ,. . in undisturbed layers of rock, the oldest rocks are on the bottom and the rocks become progressively younger toward the top.. Estimating age in the archaeological record is the primary focus of archaeological sciences. Being able to establish a timescale is what sets archaeologists apart from other disciplines. . However. , relative dating techniques are still fundamental to the discipline.. Folds, Faults and Deformities…. OH MY!!. Uniformitarianism. Geologic processes that occurred in the past can be explained by current geologic processes. Erosion and weathering that happens today must have been the same millions of years ago. a. Fossils. 3. Geologic Time Scale. 4. Geologic Belts. 5. NC Geologic History. How do we know . geologic . history. ?. Earth's History. Earth's history spans over a length of . 4.5 billion . years. Geologists have divided that time into units based on major geologic events and life forms. Relative age dating:. Age of a rock compared to other rocks. Used to understand a sequence of events. What are the ways to tell . RELATIVE AGE. .. 1. Law of Superposition (Undisturbed) . 2. Extrusion & Intrusion (Igneous Rock). Absolute and relative white cells count Absolute value (leukocytes/mm 3 = Total leukocyte count ( cells/mm 3 X Relative value(%) Example: Total leukocyte count = 6000 Segmented forms (relative no.) = 50 % Absolute vs. Relative . Age. Relative Age. Determining the age of an object in relation to other objects. “Estimate”. Index Fossils, Rock layers. Example. : A friend tells you . he . has 2 brothers – one that’s older than .