The problem is that carbon-14 decays relatively quickly, as radioactive isotopes go, so this method only works well for samples this side of 50,000 years old.
In a commentary, Chris Stringer from the Natural History Museum of London said that the Rising Star team could have tried carbon dating “even if only to test whether the material lies beyond the effective range of that method.” Hawks says they plan to but says the technique “involves destroying material, and we didn't want to do that until we had published a description of the species.”They’re also going to try to extract DNA from the fossils themselves.
I asked John Hawks, a biologist at the University of Wisconsin and one of the heads of the Rising Star expedition, to talk me through the various available methods—and why they have been difficult to apply to the latest finds.
The technique people are most likely to have heard of is carbon dating.
And once they know the age of the layers, they can tell the age of the fossils sandwiched within them.
But in southern Africa, hominid fossils are almost always found in caves like Rising Star. Instead, the bones are typically embedded within breccia—a concrete-like mixture of gravel, sand, and other junk that accumulated in the floor of the cave.
And even then, the results from ESR typically need to be cross-checked against other sources of data.
Paleontologists can sometimes date a new fossil by looking at its companions in death, by finding nearby bones of other extinct animals that died within a known timeframe.
“Or they could be millions of years apart.” He’s bracing himself for the latter.That’s impossible here, because If adjacent bones provide no clues, the surrounding landscape might.In East Africa, hominid fossils are often preserved within layers of rock, like an opera gateau that took millions of years to bake.Flowstones aside, the team can also look for layers of magnetic minerals, like particles of iron.The alignment of these minerals depends on the Earth's magnetic field, which has repeatedly flipped direction over the eons, so that north becomes south and vice versa.