Most absolute age determinations in geology rely on radiometric methods. The earth is billions of years old. The main condition for the method is that the production rate of isotopes stays the same through ages, i. The production of isotopes from chemical elements is known as decay rate and it is considered a constant. Because it is driven by sun activity it was always questioned.
An alkaline earth metal , strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is exposed to air. Strontium has physical and chemical properties similar to those of its two vertical neighbors in the periodic table, calcium and barium. It occurs naturally mainly in the minerals celestine and strontianite , and is mostly mined from these. Both strontium and strontianite are named after Strontian , a village in Scotland near which the mineral was discovered in by Adair Crawford and William Cruickshank ; it was identified as a new element the next year from its crimson-red flame test color. Strontium was first isolated as a metal in by Humphry Davy using the then newly discovered process of electrolysis.
Rubidium is the chemical element with the symbol Rb and atomic number Rubidium is a very soft, silvery-white metal in the alkali metal group. Rubidium metal shares similarities to potassium metal and caesium metal in physical appearance, softness and conductivity. Rubidium is the first alkali metal in the group to have a density higher than water , so it sinks, unlike the metals above it in the group. Rubidium has a standard atomic weight of
Potassium-argon dating , method of determining the time of origin of rocks by measuring the ratio of radioactive argon to radioactive potassium in the rock. This dating method is based upon the decay of radioactive potassium to radioactive argon in minerals and rocks; potassium also decays to calcium Thus, the ratio of argon and potassium and radiogenic calcium to potassium in a mineral or rock is a measure of the age of the sample. The calcium-potassium age method is seldom used, however, because of the great abundance of nonradiogenic calcium in minerals or rocks, which masks the presence of radiogenic calcium. On the other hand, the abundance of argon in the Earth is relatively small because of its escape to the atmosphere during processes associated with volcanism.