According to ABC net
the normal way of dating significant geological events in the Earth's past is by examining radiation levels, specifically the uranium isotopic composition of minerals. By doing so scientists can calculate, based on the rate of decay, how much time has passed since rocks or minerals were formed.
Geologists can do this by the fact that as minerals form they capture uranium, which undergoes radioactive decay to other elements, ending as lead ( a sort of clocks in the rocks
scenario). However, it now transpires that certain key geological events may well have happened more recently than previously considered. Why so?
As ARS Technica
details, surmising some new research by the British Geological Survey and the Massachusetts Institute of Technology (MIT), some geologists believe that they have devised more accurate methods for measuring uranium decay.
The specifics are a little complicated (see the journal Science
for the full details). Simply it relates to the ratio between two different isotopes of uranium called 238U and 235U, which are used to calculate the uranium-lead equation. Isotopes are variants of a particular chemical element, which means that a chemical can remain essentially the same but change its form slightly in that the number of neutrons differs from one form or 'isotope' to another (and this change can be measured).
For greater accuracy there are two 'parallel' uranium-lead decay routes
(238U to 206Pb and 235U to 207Pb), which leads to multiple dating techniques within the overall U-Pb system. To end up with a final figure geologists work out a ratio between the two types of uranium.
The new research suggests that the way of working this equation out may well have been wrong for some minerals (the researchers looked at zircon as an example).
In essence, the math may have been out for up to 700,000 years for samples that are about 4.5 billion years old. The new ratio, if it receives universal acceptance, will allow geologists to place more accurate limits on the timing of a broad range of geological processes, including the initial formation of the planet to past evolutionary events and current research into climate change.