Unit 10 Unit 10 - Uniformitarianism & the Age of the Earth Parsley, Sage, Rosemary and Time

Unit 10 Unit 10 - Uniformitarianism & the Age of the Earth Parsley, Sage, Rosemary and Time Last chapter, we did “relative time”--which came first? Now we spice it up with “absolute time”--how many years?  Count annual layers, for accurate estimates, for “short times” (less than about 100,000 years);  Calculate from recent rates and reconstructed effects, for less-accurate estimates, for short and long times (uniformitarian approach);  Use radiometric (radioactive) techniques, for accurate estimates, for short and long times.

Unit 10 Unit 10 - Uniformitarianism & the Age of the Earth Annual layers Overlapping-tree rings, to more than 10,000 years; Special-lake sediments, to more than 40,000 years; Ice-core layers, to more than 100,000 years; MANY checks, including:  reproducibility of counting;  agreement with historical records (chemically fingerprinted fallout of volcanic eruptions, etc.);  consistency amongst ice, lakes and trees for ages of abrupt climate changes;  agreement with radiometric, uniformitarian ages.

Unit 10 Unit 10 - Uniformitarianism & the Age of the Earth Old as the Hills Annual-layer records from geologically young materials (ice sheets, trees and lake sediments not turned to stone yet, on top of rocks) are much older than written history; Virtually all scientists, most religions agree Earth looks much older than written history; Some religions disagree vehemently; Whatever the truth, the science is good.

Unit 10 Unit 10 - Uniformitarianism & the Age of the Earth Climbing the Canyon Metamorphosed old mountain range at bottom; Unconformity, then two miles of sediments; Tipped by faulting, then unconformity, then another mile of sediments with several unconformities within; Rocks are “normal”, with tracks, mudcracks, etc. at many different levels, fossil changes upward; Rim rocks slant down under Zion, which is under Bryce, which is… Roughly 100 million years to deposit sediments, plus time for old metamorphics, plus erosion…

Unit 10 Unit 10 - Uniformitarianism & the Age of the Earth Radiometric Dating Half of parent atoms decay to offspring in one half-life (easy to measure; don’t need to wait for a half-life to pass, just for a measurable change); Half-life fixed by the same physics that make the sun shine and keep us from blowing up--is not a variable; Parent:offspring ratio plus half-life give age; Requires a little care and attention; Agrees with written records, layer counts, uniformitarian calculations, other radiometric techniques.

Unit 10 Unit 10 - Uniformitarianism & the Age of the Earth Radiometric Dating Example Solid potassium-40 parent included in lava flows, but gaseous argon-40 offspring escapes; After flow hardens, additional argon-40 produced from potassium-40 is trapped; 1.3-billion-year half-life; If you start with 400 parents, after one half-life (1.3 billion years) average 200 parents left (and 200 offspring), after second half-life (total 2.6 billion years) average 100 parents left (and 300 offspring), after third half-life (total 3.9 billion years) average 50 parents left (and 350 offspring), …

Unit 10 Unit 10 - Uniformitarianism & the Age of the Earth Inches and a Cloud of Dust Oldest rocks about 4 billion years old, but Earth bombarded, melted first; Meteorites formed with Earth; they are about 4.6 billion years old (agrees with whole-Earth estimates); If 4.6 billion years is the 100-yard length of a football field, written history is about the thickness of a sheet of paper, and a 20-year- old student has lived through inches.