Revolution in dating methods: Rethinking timelines of human evolution

A new study conducted by scientists from the Australian National University in Canberra and the Natural History Museum in London calls for a thorough reassessment of previous theories about human evolution and the timelines associated with different types of hominids. This is largely due to a newfound approach to dating remains.

Radiocarbon dating, one of the most prevalent methods for determining the age of a specimen, focuses on the content of one of the radioactive isotopes of carbon. Carbon-14, a radioactive isotope, accumulates in the tissues of animals and plants throughout their lifetime. This absorption occurs in tissues universally, whether from an insect, fern, mammoth, or blue whale. However, this absorption process ceases once these organisms die.

Carbon-14 is the only naturally occurring isotope of this element that is radioactive, and its half-life is around 5730 years. Thus, a bone or a piece of wood that was used by an ancient Mesopotamian craftsperson approximately 6,000 years ago would have half the amount of carbon-14 compared to modern specimens. This forms the basis for approximating the age of finds, but there are some limitations.

The methodology becomes unreliable for extremely ancient materials, such as those from the dinosaur era. The remaining amount of carbon-14 becomes negligible, making it difficult to base calculations on it. The method is not efficient for finds that might be older than around 50,000 years. There have also been significant errors suggesting far younger samples than the actual.

An error of this nature happened during the dating of remains from hominids called Homo floresiensis that were found on the island of Flores. Instead of analyzing the remains directly, researchers examined the embedded sediment. The hominids were mistakenly believed to have roamed 12,000 years ago when they actually inhabited the island around 60,000 years back.

For this reevaluation, radiometric dating was again employed, but the carbon-14 levels were not considered. The team employed an alternative technique known as uranium-thorium dating. Even though this method has been in use for fifty years, recent improvements by the Canberra and London-based scientists have achieved unprecedented precision.

Assessing uranium levels, with its half-life of 4.5 billion years, is generally more reliable but also more demanding, as uranium deposits deep inside tissues. To ascertain the age of a valuable relic previously, it was necessary to physically slice it in half to obtain essential samples — a practice that has inflicted irreversible damage on countless collections. The current approach has miniaturized the process, making sample collection from deep tissues achievable with the help of a laser.

This groundbreaking method opens the door to retesting thousands of samples globally for a more accurate age determination. This could prompt a new outlook in the scientific community toward the history of our species' evolution.