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Quiz Three (9:30-9:35 AM) UNIVERSITY OF SOUTH ALABAMA

GY 112: Earth

Lecture 7 & 8: Dating

Instructor: Dr. Douglas W. Haywick Last

1. William Smith and Water 2. Stratigraphic Principles 3. Geological Time

(Web Lecture 6) Clever thinkers: 1769-1839

William “Strata” Smith: He recognized the importance of in distinguishing different geological or “stratigraphic” units. Stratigraphic Nomenclature

Formation: a lithologically distinct unit that possesses recognizable upper and lower contacts with other units and which can be traced across the countryside from place to place.

Corso Member: an important “unit” Group but one not quite meeting the requirements of a formation

Group: a collection of similar type formations

Source: 3dparks.wr.usgs.gov/coloradoplateau/images/bryce_strat.jpg Geological Time

The problem is that we have to deal with a lot of time.

4.6 GA = 4,600,000,000 years Geological Time

Time Eon Time 0 MA (today) Phanerozoic Cenozoic 65 MA to 0 MA

Mesozoic 245 MA to 65 MA

Paleozoic 550 MA to 245 MA

Proterozoic Neoproterozoic 900 MA to 550 Ma

Mesoproterozoic 1.6 GA to 900 MA

Paleoproterozoic 2.5 GA to 1.6 GA

Archean 4.1 Ga to 2.5 Ga 4.6 GA Hadean 4.6 Ga to 4.1 Ga Geological Time

Periods: the most 65 MA useful subdivisions of (mostly) the 245 MA Phanerozoic eon

550 MA Pennsylvanian

Mississippian

Hadean Today’s Agenda

1. Relative vs. Techniques a) Magnetostratigraphy b) Fission Track Dating 2. 3. Mass spectrophotometers

(Web Lectures 7 & 8) Dating

Geologists can time events by putting them in order of occurrence.

But, this does not allow you to actually date when those events actually occurred.

Source: http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/time/graphics/history1e.gif Geological Dating Techniques

Relative Techniques: Assigns an age to a rock that puts it into a narrow range (e.g., mid-Devonian; Late Cretaceous, upper Pliocene).

Geological Dating Techniques

Relative Techniques: Assigns an age to a rock that puts it into a narrow range (e.g., mid-Devonian; Late Cretaceous, upper Pliocene).

Absolute Techniques: Assigns an age to a rock that is a number (e.g., 354.7 +/- 21.3 MA; 1,453 KA +/- 67 KA). Geological Dating Techniques

Relative Techniques: (), stable isotope , /magnetostratigraphy)

Source: http://www.ideofact.com/archives/trilobite.jpg Geological Dating Techniques

Relative Techniques: paleontology (biostratigraphy), stable isotope stratigraphy, paleomagnetism)

Silurian Ordovician Cambrian Geological Dating Techniques

Absolute Techniques: fission track dating, radiometric dating

Source: http://www.geo.umn.edu/people/grads/bair0042/MFT.html Relative Dating

Magnetic Stratigraphy or Magnetostratigraphy

Recall: Paleomagnetism Magnetostratigraphy

•The Earth has a magnetic field N •north is north and south is south, but…

S Magnetostratigraphy

•The Earth has a magnetic field S •north is north; south is south, but…

…. It hasn’t always been that way

Magnetic reversals N Magnetostratigraphy

• Magnetization of ancient rocks at the time of their formation is a good piece of evidence supporting plate tectonics….

Source: http://piru.alexandria.ucsb.edu/collections/geosyst ems/geosystems11-15.jpg Magnetostratigraphy

• Magnetization of ancient rocks at the time of their formation is a good piece of evidence supporting plate tectonics….

….. and, it allows us to date rocks (kind of)

Source: http://piru.alexandria.ucsb.edu/collections/geosyst ems/geosystems11-15.jpg Magnetostratigraphy

• Reversals in polarity of field are recorded in rocks when they crystallize and as they settle from water

Magnetometer Magnetostratigraphy

• Reversals in polarity of field are recorded in rocks when they crystallize and as they settle from water

• Vertical successions of Magnetometer record changes in magnetic field over time

Magnetostratigraphy

A portion of the paleomagnetic record from 10 MA to 0 MA (today) Magnetostratigraphy

• Chron – Polarity time-rock unit Magnetostratigraphy

• Chron – Polarity time-rock unit – Period of normal or reversed polarity • Normal interval – Same as today – Black • Reversed interval – Opposite to today – White Magneto- stratigraphy Absolute Dating

Fission Track Dating Fission Track Dating

The Periodic Table of the elements Fission Track Dating

Radioactive elements are unstable Absolute Techniques

• Fission-Track Dating – Measure decay of uranium 238 by counting number of tracks Absolute Techniques

• Fission-Track Dating – Measure decay of uranium 238 by counting number of tracks Radiometric Dating

Uranium (and others) are unstable Radioactive Decay Radioactive Decay

Three modes of decay Radioactive Decay

Three modes of decay 1) Alpha Decay Loss of alpha particle • Convert parent into element that has nucleus containing two fewer protons

U235 → Pb207 Radioactive Decay

Three modes of decay 1) Alpha Decay Loss of alpha particle • Convert parent into element that has nucleus containing two fewer protons 2) Beta Decay Loss of beta particle • Convert parent into element whose nucleus contains one more proton by losing an electron

C14 → N14

Radioactive Decay

Three modes of decay 1) Alpha Decay Loss of alpha particle • Convert parent into element that has nucleus containing two fewer protons 2) Beta Decay Loss of beta particle • Convert parent into element whose nucleus contains one more proton by losing an electron 3) Gamma Decay Capture of beta particle • Convert parent into element whose nucleus has one less proton K40→ Ar40 Radioactive Decay

Alpha Decay (Uranium)

238U → 206Pb + 8α http://mike.gamerack.com/science/halflifeu238.gif Radioactive Decay

• Radiometric dating – Radioactive isotopes decay at constant geometric rate • After a certain amount of time, half of the parent present will survive and half will decay to daughter

Radioactive Decay

• Radiometric dating – Radioactive isotopes decay at constant geometric rate • After a certain amount of time, half of the parent present will survive and half will decay to daughter • Half-life – Interval of time for half of parent to decay

Absolute Age

• Absolute ages change – Error increases in older rocks – Techniques change

• Biostratigraphic correlations may be more accurate Half Lives

Parent Isotope Daughter Isotope Half Life (years) Datable Material(s) 14C (Carbon-14) 14N (Nitrogen-14) Wood, shells and organic material 235U (Uranium-235) 207Pb (Lead-207) Metamorphic, igneous rocks, Zircon, U-bearing minerals 40K (Potassium-40) 40Ar (Argon-40) Metamorphic, igneous & sedimentary rocks; -bearing minerals 238U (Uranium-238) 206Pb (Lead-206) Metamorphic, igneous rocks, Zircon, U-bearing minerals 232Th (Thorium-232) 208Pb (Lead-208) Metamorphic, igneous rocks, Zircon, U-bearing minerals 87Rb (Rubidium-87) 87Sr (Strontium-87) Various rocks and minerals 147Sm (Samarium-147) 143Nd (Neodymium-143) Very old rocks, REE bearing minerals Half Lives

Parent Isotope Daughter Isotope Half Life (years) Datable Material(s) 14C (Carbon-14) 14N (Nitrogen-14) 5,730 Wood, shells and organic material 235U (Uranium-235) 207Pb (Lead-207) Metamorphic, igneous rocks, Zircon, U-bearing minerals 40K (Potassium-40) 40Ar (Argon-40) Metamorphic, igneous & sedimentary rocks; feldspar-bearing minerals 238U (Uranium-238) 206Pb (Lead-206) Metamorphic, igneous rocks, Zircon, U-bearing minerals 232Th (Thorium-232) 208Pb (Lead-208) Metamorphic, igneous rocks, Zircon, U-bearing minerals 87Rb (Rubidium-87) 87Sr (Strontium-87) Various rocks and minerals 147Sm (Samarium-147) 143Nd (Neodymium-143) Very old rocks, REE bearing minerals Half Lives

Parent Isotope Daughter Isotope Half Life (years) Datable Material(s) 14C (Carbon-14) 14N (Nitrogen-14) 5,730 Wood, shells and organic material 235U (Uranium-235) 207Pb (Lead-207) 700,000,000 Metamorphic, igneous rocks, Zircon, U-bearing minerals 40K (Potassium-40) 40Ar (Argon-40) Metamorphic, igneous & sedimentary rocks; feldspar-bearing minerals 238U (Uranium-238) 206Pb (Lead-206) Metamorphic, igneous rocks, Zircon, U-bearing minerals 232Th (Thorium-232) 208Pb (Lead-208) Metamorphic, igneous rocks, Zircon, U-bearing minerals 87Rb (Rubidium-87) 87Sr (Strontium-87) Various rocks and minerals 147Sm (Samarium-147) 143Nd (Neodymium-143) Very old rocks, REE bearing minerals Half Lives

Parent Isotope Daughter Isotope Half Life (years) Datable Material(s) 14C (Carbon-14) 14N (Nitrogen-14) 5,730 Wood, shells and organic material 235U (Uranium-235) 207Pb (Lead-207) 700,000,000 Metamorphic, igneous rocks, Zircon, U-bearing minerals 40K (Potassium-40) 40Ar (Argon-40) 1,300,000,000 Metamorphic, igneous & sedimentary rocks; feldspar-bearing minerals 238U (Uranium-238) 206Pb (Lead-206) Metamorphic, igneous rocks, Zircon, U-bearing minerals 232Th (Thorium-232) 208Pb (Lead-208) Metamorphic, igneous rocks, Zircon, U-bearing minerals 87Rb (Rubidium-87) 87Sr (Strontium-87) Various rocks and minerals 147Sm (Samarium-147) 143Nd (Neodymium-143) Very old rocks, REE bearing minerals Half Lives

Parent Isotope Daughter Isotope Half Life (years) Datable Material(s) 14C (Carbon-14) 14N (Nitrogen-14) 5,730 Wood, shells and organic material 235U (Uranium-235) 207Pb (Lead-207) 700,000,000 Metamorphic, igneous rocks, Zircon, U-bearing minerals 40K (Potassium-40) 40Ar (Argon-40) 1,300,000,000 Metamorphic, igneous & sedimentary rocks; feldspar-bearing minerals 238U (Uranium-238) 206Pb (Lead-206) 4,500,000,000 Metamorphic, igneous rocks, Zircon, U-bearing minerals 232Th (Thorium-232) 208Pb (Lead-208) Metamorphic, igneous rocks, Zircon, U-bearing minerals 87Rb (Rubidium-87) 87Sr (Strontium-87) Various rocks and minerals 147Sm (Samarium-147) 143Nd (Neodymium-143) Very old rocks, REE bearing minerals Half Lives

Parent Isotope Daughter Isotope Half Life (years) Datable Material(s) 14C (Carbon-14) 14N (Nitrogen-14) 5,730 Wood, shells and organic material 235U (Uranium-235) 207Pb (Lead-207) 700,000,000 Metamorphic, igneous rocks, Zircon, U-bearing minerals 40K (Potassium-40) 40Ar (Argon-40) 1,300,000,000 Metamorphic, igneous & sedimentary rocks; feldspar-bearing minerals 238U (Uranium-238) 206Pb (Lead-206) 4,500,000,000 Metamorphic, igneous rocks, Zircon, U-bearing minerals 232Th (Thorium-232) 208Pb (Lead-208) 14,000,000,000 Metamorphic, igneous rocks, Zircon, U-bearing minerals 87Rb (Rubidium-87) 87Sr (Strontium-87) Various rocks and minerals 147Sm (Samarium-147) 143Nd (Neodymium-143) Very old rocks, REE bearing minerals Half Lives

Parent Isotope Daughter Isotope Half Life (years) Datable Material(s) 14C (Carbon-14) 14N (Nitrogen-14) 5,730 Wood, shells and organic material 235U (Uranium-235) 207Pb (Lead-207) 700,000,000 Metamorphic, igneous rocks, Zircon, U-bearing minerals 40K (Potassium-40) 40Ar (Argon-40) 1,300,000,000 Metamorphic, igneous & sedimentary rocks; feldspar-bearing minerals 238U (Uranium-238) 206Pb (Lead-206) 4,500,000,000 Metamorphic, igneous rocks, Zircon, U-bearing minerals 232Th (Thorium-232) 208Pb (Lead-208) 14,000,000,000 Metamorphic, igneous rocks, Zircon, U-bearing minerals 87Rb (Rubidium-87) 87Sr (Strontium-87) 48,600,000,000 Various rocks and minerals 147Sm (Samarium-147) 143Nd (Neodymium-143) Very old rocks, REE bearing minerals Half Lives

Parent Isotope Daughter Isotope Half Life (years) Datable Material(s) 14C (Carbon-14) 14N (Nitrogen-14) 5,730 Wood, shells and organic material 235U (Uranium-235) 207Pb (Lead-207) 700,000,000 Metamorphic, igneous rocks, Zircon, U-bearing minerals 40K (Potassium-40) 40Ar (Argon-40) 1,300,000,000 Metamorphic, igneous & sedimentary rocks; feldspar-bearing minerals 238U (Uranium-238) 206Pb (Lead-206) 4,500,000,000 Metamorphic, igneous rocks, Zircon, U-bearing minerals 232Th (Thorium-232) 208Pb (Lead-208) 14,000,000,000 Metamorphic, igneous rocks, Zircon, U-bearing minerals 87Rb (Rubidium-87) 87Sr (Strontium-87) 48,600,000,000 Various rocks and minerals 147Sm (Samarium-147) 143Nd (Neodymium-143) 106,000,000,000 Very old rocks, REE bearing minerals Age Determination

Mass Spectrophotometer Age Determination

The all important age equation:

-λt N=Noe

No is the number of atoms of parent isotope remaining in a substance N is the number of atoms of daughter isotope produced through decay, λ is the decay constant (which depend on the isotope in question) t is the amount of elapsed time. Age Determination

A more useful equation for age determination:

Rock age= 1/λ x ln[(Do-D) + 1] N Do is the original amount of daughter isotope in the sample N is the amount of current parent isotope in the sample D is the amount of current daughter isotope in the sample

λ is the decay constant Today’s Homework

1. Review online notes 2. Read War and Peace

Next Time

Lectures 8a: Stable isotope hardcore chemistry!

Heads-up for next week’s lab Bring Scientific calculator to lab ! GY 112: Earth History

Lectures 7, 8: Dating Instructor: Dr. Doug Haywick [email protected]

This is a free open access lecture, but not for commercial purposes. For personal use only.