Example of absolute dating geology
Rubidium-strontium (Rb-Sr) dating: Radioactive rubidium-87 decays into strontium-87 with a half -life of 48.8 billion years.
Not surprisingly, Ru-Sr dating is used to date very old rocks (as old as the Earth, in fact, since the Earth is "only" around 4.6 billion years old).
The half-life of uranium-238 is 4.47 billion years, while that of uranium-235 is 704 million years.
Because these differ by a factor of almost seven (recall that a billion is 1,000 times a million), it proves a "check" to make sure you're calculating the age of the rock or fossil properly, making this among the most precise radiometric dating methods.
This is because when radioactive elements first come into being, they are presumed to consist entirely of a single isotope.
Imagine that you enjoy a certain kind of ice cream flavored with chocolate chips.
U-Pb dating is complex because of the two isotopes in play, but this property is also what makes it so precise.
The method is also technically challenging because lead can "leak" out of many types of rocks, sometimes making the calculations difficult or impossible.
The number refers to the number of protons plus neutrons.
You also need to know when you can or cannot apply a particular type of device to the task at hand; for example, if you want to know how hot it is on the inside of an active wood stove, you probably understand that putting a household thermometer intended to measure body temperature inside the stove is not going to prove helpful.
Be aware also that for many centuries, most human "knowledge" of the age of rocks, formations such as the Grand Canyon, and everything else around you was predicated on the Genesis account of the Bible, which posits that the entire cosmos is perhaps 10,000 years old.
Uranium's atomic number is 92, corresponding to its number of protons.
which decay into lead-206 and lead-207 respectively.