Use of radiocarbon dating
Trees maintain carbon 14 equilibrium in their growth rings—and trees produce a ring for every year they are alive.
Although we don't have any 50,000-year-old trees, we do have overlapping tree ring sets back to 12,594 years.
Other organic data sets examined have included varves (layers in sedimentary rock which were laid down annually and contain organic materials, deep ocean corals, speleothems (cave deposits), and volcanic tephras; but there are problems with each of these methods.
Cave deposits and varves have the potential to include old soil carbon, and there are as-yet unresolved issues with fluctuating amounts of C14 in ocean corals.
We should see some interesting results in the very near future.
Within the last few years, a new potential source for further refining radiocarbon curves is Lake Suigetsu in Japan.
Today, the radiocarbon-14 dating method is used extensively in environmental sciences and in human sciences such as archaeology and anthropology.
It also has some applications in geology; its importance in dating organic materials cannot be underestimated enough.
So, in other words, we have a pretty solid way to calibrate raw radiocarbon dates for the most recent 12,594 years of our planet's past.
As you might imagine, scientists have been attempting to discover other organic objects that can be dated securely steadily since Libby's discovery.