Rubidium-strontium (Rb-Sr) dating: Radioactive rubidium-87 decays into strontium-87 with a half -life of 48.8 billion years.
It's simple: You must have started with a total of 80 chips, because you now have 70 10 = 80 total additives to your ice cream.
Because your roommate eats half of the chips on any given day, and not a fixed number, the carton must have held 20 chips the day before, 40 the day before that, and 80 the day before that.
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.
Calculations involving radioactive isotopes are more formal but follow the same basic principle: If you know the half-life of the radioactive element and can measure how much of each isotope is present, you can figure out the age of the fossil, rock or other entity it comes from.
Scientists interested in figuring out the age of a fossil or rock analyze a sample to determine the ratio of a given radioactive element's daughter isotope (or isotopes) to its parent isotope in that sample.
Sure, you can scour the Internet and learn rather quickly that the scientific consensus pins the age of of the planet at about 4.6 billion years.
But Google didn't invent this number; instead, human ingenuity and applied physics have provided it.
Uranium's atomic number is 92, corresponding to its number of protons.
which decay into lead-206 and lead-207 respectively.
Uranium-lead (U-Pb) dating: Radioactive uranium comes in two forms, uranium-238 and uranium-235.