K and U move together during geochemical processes and have long-lived radioisotopes that emit gamma rays. It is calculated as a ratio of one to the other on an equal mass basis which is often .
This creates a compelling explanation for the evolution of the solar system.
This result is consistent with an increasing temperature toward the sun during its early protoplanetary nebula phase.
The temperature at the early stage of solar system formation was in excess of 1,000K at the distance of Earth from the sun, and as low as 200–100K at the distances of Jupiter and Saturn.