eva dating sim cheats - Rubidium dating
The mantle is a lot poorer in Rb than Sr and its Sr-87 content increases slowly.Extrapolating back 4.6 billion years, the ratio just after the earth formed would have been about 0.699.
Early attempts at Rubidium-Strontium dating made use of the fact that the Sr-87/Sr-86 ratio in rubidium-poor samples was about 0.7.
Since these samples were poor in rubidium, it could be assumed that the primordial ratio of Sr-87 to Sr-86 was 0.7.
Where the isochron crosses the vertical axis corresponds to a hypothetical sample with no rubidium at all.
In other words, the Sr-87/Sr-86 ratio there is the content the rock had before any rubidum decayed.
Rocks derived from recycling of crustal material are derived from sources that have had time to accumulate radiogenic Sr-87, and can have initial ratios of 0.710 or greater.