TIME

PRS Figure out at what time you put on your shoes this morning (assuming you are wearing shoes). What dating technique did you use? A. Numerical Time B. Relative Time C. both

PRS Which type of time reckoning do you use most often? A. Numerical Time B. Relative Time

Bishop Ussher – Earth formed 4004 B. C Bishop Ussher – Earth formed 4004 B.C. –October 23 – using Biblical history GROUP QUESTION: Think of another way to come up with a minimum age for the earth (do not use radioactivity)

Uniformitarianism - James Hutton "no vestige of a beginning, no prospect of an end." “The present is the key to the past” But rates of processes change – so only things that are constant are physical laws.

Original Horizontality Superposition Crosscutting Relationships Inclusions

Group Question Using your experience with sediments, like the sand on a beach, is there a problem with Steno’s Principle of Original Horizontality? If so, what?

Unconformities

Group Question Going back to your beach, is there an unconformity there? Most of Geologic time is represented by unconformities

Crosscutting Relationships Inclusions

Which is older Dike A Dike B Fault Dolostone Sandstone B

William “Strata” Smith Engineer Surveyor Biostratigrapher

William “Strata” Smith 1769-1839: canal engineer, first stratigrapher

Wm. Smith’s canals today

Geologic Time Scale Pieced together through correlation Dates come from radioactivity

Relative Time vs. Absolute (Numerical) Time Bishop Ussher – Earth formed 4004 B.C. –October 23 – using Biblical history GROUP QUESTION: Think of another way to come up with a minimum age for the earth (do not use radioactivity)

Atoms

Isotopes 6 protons 6 protons 6 protons 6 neutrons 7 neutrons 8 neutrons

PRS If an atom with 19 protons and 20 neutrons is an isotope of Potassium, Which of the following is another isotope of Potassium? 20 p, 19 n 20 p, 21 n 19 p, 22 n 20 p, 22 n 18 p, 22 n

Radioactivity Parent Daughter

Need to know 4 things Sample had some parent at start Sample has been “closed system” Decay rate of parent-daughter pair Parent-daughter ratio at start Need to measure 1 thing Parent-daughter ratio now

Industrial revolution added C12 – diluting the C14 Nuclear Bomb Tests added C14

C14 Calibration

Why don’t geologists use 14 C to date rocks? Half life is too long Rocks aren’t closed systems Rocks don’t have any Carbon Rocks don’t get carbon from atmosphere Rocks have too much 14 C

K – Ar dating HL 1.26 BY Daughter is noble gas

(compiled from Dalrymple, 1991) Technique Age Range (billion years) uranium-lead 3.60±0.05 lead-lead 3.56±0.10 3.74±0.12 3.62±0.13 rubidium-strontium 3.64±0.06 3.62±0.14 3.67±0.09 3.66±0.10 3.61±0.22 3.56±0.14 lutetium-hafnium 3.55±0.22 samarium-neodymium 3.56±0.20 (compiled from Dalrymple, 1991)

Geologic Time Scale Pieced together through correlation Dates come from radioactivity

Correct answer for 8.3 Youngest J E C A G B I D F H Oldest