We could use rock datation, but most of them are unreachable, am I right? Think that you are standing in front of a group of 2000 people and you want to know who is the oldest person in that crowd, but you can only ask the age of the 10 or so people standing right next to you. what Michael is eluding to is that you need a large enough sample, because radioactive dating basically uses a ratio of the amount of material that has decayed relative to the amount that has not decayed.
"The meteorite" as an object, since it is by definition a remnant from a meteoroid and later a meteor, was formed on impact.
The dating equation used for K-Ar is: Carbon Dating Radiocarbon dating is different than the other methods of dating because it cannot be used to directly date rocks, but can only be used to date organic material produced by once living organisms.
Some background: We are able to determine the age of certain rocks and minerals using measurements of radioactive and radiogenic isotopes of certain elements. Simply put, the resulting date is the time that has passed from the crystallisation of that mineral.
Thus, if we start out with 1 gram of the parent isotope, after the passage of 1 half-life there will be 0.5 gram of the parent isotope left.
After the passage of two half-lives only 0.25 gram will remain, and after 3 half lives only 0.125 will remain etc.U leakage would cause discordant points to plot above the cocordia. Lunar rocks also lie on the Geochron, at least suggesting that the moon formed at the same time as meteorites. Pb separated from continents and thus from average crust also plots on the Geochron, and thus suggests that the Earth formed at the same time as the meteorites and moon.