Quiz Three (9:30-9:35 AM) UNIVERSITY OF SOUTH ALABAMA
GY 112: Earth History
Lecture 7 & 8: Dating
Instructor: Dr. Douglas W. Haywick Last Time
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 fossils in distinguishing different geological or “stratigraphic” units. Stratigraphic Nomenclature
Formation: a lithologically distinct rock 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 Era 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. Absolute Dating Techniques a) Magnetostratigraphy b) Fission Track Dating 2. Radiometric Dating 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: paleontology (biostratigraphy), stable isotope stratigraphy, paleomagnetism/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 sedimentary rock 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; 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) 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 geochemistry 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.