dating methods
DESCRIPTION
Dating Methods. 10.11.07 / 10.12.07. Essential Question. How can scientists determine the ages of geologic material?. What are strata?. Layers of rock. Strata. Strata. Folded strata. What is an angular unconformity?. - PowerPoint PPT PresentationTRANSCRIPT
What is an angular unconformity?
• When rock deposited in horizontal layers is folded or tilted, then eroded, and then covered by more horizontal layering
What is the law of cross-cutting relationships?
• The fault or igneous intrusion is always younger than the rock layer it cuts through.
What are nonconformities?
• Unstratified igneous or metamorphic rock is eroded and then covered by layers of sediment.
What are disconformities?
• The boundary between younger sedimentary rock layers deposited on an eroded layer of older sedimentary rock
Earth history in 24 hours
scale:
1 sec = 52,000 years
1 min = 3,125, 000 yrs
1 hour = 187,500,000 yrs
Rates of erosion and deposition
• Measure the recent rates
• Estimate age of geologic feature– Becomes less reliable as age increases– Most reliable within last 10,000-20,000 years
Varve count
• Similar to counting tree rings
• Count annual layers of sediment
• Common in glacial lake beds
• Distinguished by layers of dark fine particals and light heavy particles
Radiometric dating
• A method of determining the absolute age of an object by comparing the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope.
• Atoms of the same element with different numbers of neutrons are called isotopes.
Radioactivity and radiometric dating
Radiometric dating • Half-life – the time for one-half of the
radioactive nuclei to decay • Requires a closed system• Cross-checks are used for accuracy • Complex procedure • Yields numerical dates
Radioactivity and radiometric dating
Carbon-14 dating • Half-life of only 5730 years • Used to date very recent events • Carbon-14 produced in upper atmosphere
• Incorporated into carbon dioxide • Absorbed by living matter
• Useful tool for anthropologists, archeologists, historians, and geologists who study very recent Earth history