Lead–lead dating

If the sample behaved as a closed system then graphing the difference between the present and initial ratios of 207Pb/204Pb versus 206Pb/204Pb should produce a straight line.

Assuming the process of elemental differentiation is identical on Earth as it is on other planets, the core of these planetesimals would be depleted of uranium and thorium, while the crust and mantle would contain higher U/Pb ratios.

Samples of iron meteorite from Canyon Diablo (Meteor Crater) Arizona were found to have the least radiogenic composition of any material in the solar system.

Therefore, troilite found in Canyon Diablo represents the primeval lead isotope composition of the solar system, dating back to 4.55±0.07 Byr.

Stony meteorites however, exhibited very high 207Pb/204Pb versus 206Pb/204Pb ratios, indicating that these samples came from the crust or mantle of the planetesimal.

Patterson also analyzed terrestrial sediment collected from the ocean floor, which was believed to be representative of the Bulk Earth composition.

Chondrules and calcium–aluminium-rich inclusions (CAIs) are spherical particles that make up chondritic meteorites and are believed to be the oldest objects in the Solar System.

Hence precise dating of these objects is important to constrain the early evolution of the Solar System and the age of the Earth.

The U–Pb dating method can yield the most precise ages for early Solar System objects due to the optimal half-life of 238U.

To avoid this problem, researchers[5] developed an 'alternative Pb–Pb isochron diagram' (see figure) with reduced error correlation between the measured ratios.