12-3) Dating with Radioactivity Flashcards
what is radioactive decay?
when an unstable nucleus spontaneously breaks apart or decays, releasing energy. the number of protons in an atom changes and a new element is formed
what is beta decay?
when an atom of an unstable isotope decays, one of its neutrons breaks down into a proton and electron, the electron which leaves the atom as beta particle.
Nucleus loses a neutron but gains a proton resulting in a new element
what is alpha decay?
when the isotope gives off two protons and two neutrons as an alpha particle
where do radioactive elements occur?
naturally in igneous rock
what are radioactive isotopes? give an example.
decay that occurs with steps. uranium-238 decays eventually into lead-206, doesnt decay further since lead isnt radioactive. Parent material is uranium-238 (unstable) and daughter product is lead-206 (stable).
what is a half life?
time it takes for half of the unstable atoms in the isotope to decay into stable isotopes (Carbon half life is 5730 years, takes 5730 for half of carbon-14 to decay to nitrogen-14, 2 half lives = 1/4 of C-14)
as time passes concentration of parent material in rock …
decreases, concentration of daughter material increases
problems with radiometric dating assumptions?
Absolute dating is not necessarily accurate: “The Fact of Life: Shattering the Myth of Darwinism” states that scientists find fossils shooting straight up through several layers of rock, lava from an eruption was only 200 years old, not three billion years, fossilized trees would have rotted, etc
four problems with accuracy of absolute dating?
- Earth may have changed in it’s rate of radioactive decay. evolution based on change, why does radioactive decay stay the same?
- Earth (rock’s in Earth) may have been created with “apparent” age. maybe rocks were created looking “old”
- Individual fossils are buried over “millions” of years of sediment. would have rotted before fossilized
- Examples of major errors in age dating of rocks
explain how carbon-14 is used to date charcoal, wood, and fossils
Animals and plants made of carbon, when they die carbon left and decays into nitrogen-14 which escapes as gase. Remaining carbon determines age of fossil
what is intrusion and extrusion?
extrusion: when magma reaches surface and cools, can conclude age of shale which is younger than extrusion
Intrusion: when magma travels through rock cracks and solidifies, shale is older
