Chapter 4. Geologic Time: Concepts and Principles. Grand Canyon. When looking down into the Grand Canyon, we are really looking at the early history of Earth. Grand Canyon. More than 1 billion years of history are preserved, like pages of a book, in the rock layers of the Grand Canyon
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Geologic Time:Concepts and Principles
is absolute dating
= number of protons + number of neutrons
b. As time passes, parent atoms decay to daughters.
a. A mineral has just crystallized from magma.
c. Metamorphism drives the daughters out of the mineral as it recrystallizes.
d. Dating the mineral today yields a date of 350 million years = time of metamorphism, provided the system remains closed during that time.
Dating the whole rock yields a date of 700 million years = time of crystallization.
Parents Daughters Half-Life (years)
Most of these are useful for dating older rocks
Uranium 238 Lead 206 4.5 billion
Uranium 234 Lead 207 704 million
Thorium 232 Lead 208 14 billion
Rubidium 87 Strontium 87 48.8 billion
Potassium 40 Argon 40 1.3 billion