Transcript Introduction to Absolute (Radiometric) Dating

Introduction to Absolute
(Radiometric) Dating
Learning Targets
Essential Question
4a) I can distinguish between
absolute and relative
dating. (DOK 1)
4b) I can define what an isotope
is and describe how
radioactive isotopes decay
(DOK 1)
4e) I can identify and analyze key
strengths and limitations of
using radioactive decay in
absolute dating. (DOK 1-2)
• How do scientists use
absolute dating to build a
model of the Earth’s
history?
Absolute Dating
Isotopes
• Two or more of the same element with
different masses.
• Have the same number of protons but
number of neutrons changes.
http://education.jlab.org/glossary/isotope.gif
Isotopes
http://www.radtrainonline.com/free/viewslide.asp?CourseID=92&ModuleID=353&SlideID=6291
Radioactivity
o Some atoms are not stable
o These atoms emit particles to achieve
stability
http://abyss.uoregon.edu/~js/images/radioactivity.gif
Radioactivity
There are three types of particles
emitted:
1. Alpha particles
2. Beta Particles
3. Gamma Rays
Alpha Particles
o Charge = +2 (2 protons)
o Mass = 4 (2 protons + 2 neutrons)
o Large, easily stopped by paper
© The Geological Society of America, 2003
Beta Particles
o Charge = -1
o Mass = negligible
o Small, more penetrating particle, but still
easily stopped
http://sol.sci.uop.edu/~jfalward/elementaryparticles/betaparticleenergy.JPG
Beta Particles
o Neutron decays into a proton and an
electron
o Electron leaves
o Atomic number goes up 1
http://sol.sci.uop.edu/~jfalward/elementaryparticles/betaparticleenergy.JPG
Gamma Rays
o Pure energy
o No change in atom
o Very penetrating, cause damage
http://www.arpansa.gov.au/images/basics/all_pen.jpg
Absolute (Radiometric) Dating
o Based on decay
rates of different
atoms
o Rate of decay
stated as half-life
http://www.bible.ca/tracks/dating-radiometric-cartoon.gif
Half-Life
• Time it takes for ½ of the radioactive atoms to
decay into its daughter atoms
© The Geological Society of America, 2003
Half-Life
• Atoms used in geologic dating have long halflives
Parent
Daughter
Half-Life
Uranium-238
Lead-206
4,470 million years
Uranium-235
Lead-207
704 million years
Potassium-40
Argon-40
1,250 million years
Rubidium-87
Strontium-87
48,800 m. y.
Carbon-14
Nitrogen-14
5,730 years
Half-Life
• Scientists use both decay and production
curves
© The Geological Society of America, 2003
Assigning Ages
• Using the proportion of daughter atom in a sample,
its age can be determined
http://upload.wikimedia.org/wikiversity/en/thumb/4/4b/Radiometricdatingmineral.png/400px-Radiometricdatingmineral.png
Major Principle of Absolute Dating
Check for Understanding
• Explain the main concepts of how scientists
use absolute (radiometric) dating to
determine the age of objects