Rb sr dating wikipedia
See the decay chain link in the See Also section below for decay chain details. It involves the radioactive nuclide Carbon-14 (aka radiocarbon) decaying to Nitrogen-14 with a 5730 year half-life.
As you can imagine, this half-life is short with respect to the age of the Earth, so it can’t be used to date rocks.
Meteorites, on the other hand, have been floating around in space since the solar system was formed.
When they come crashing to Earth, analysis of their composition can be geologically analyzed.
The isochron method can determine the age of any rock, but new rocks are formed all the time.
So to figure out the age of the Earth, we have to look somewhere else... Earth has a molten magma layer and plate tectonics, so the "closed system" requirement of these radiometric dating methods is sometimes difficult to satisfy for Earth itself.
They are all consistent with Patterson’s measurement. The mathematical details of the lead-lead isotopic clock are less straightforward than those of the Rb-Sr method.
Though the Rb and Sr concentrations differ, it’s safe to assume that the isotopic makeup of Sr and of Rb is the same everywhere.
This is the key to figuring out how much time has passed since the rock solidified.
You may have heard that the Earth is 4.54 billion years old. If the half-life of a material is 100 years and you have 1 kg of it, 100 years from now you will only have 0.5 kg of it.
This was calculated by taking precise measurements of things in the dirt and in meteorites and using the principles of radioactive decay to determine an age. The rest will have decayed into a different nuclide (called a nuclide).