» Home > In the News

Rancho La Brea

1 September 2023
Catastrophism, Dating, Geology

This is an interesting story and it really hinges around dating methodology – see https://science.org/doi/10.1126/science.abo3594 … We now have a pre-Younger Dryas megafaunal extinction at Rancho La Brea – linked to landscape fire. The Younger Dryas boundary event theory had previously associated landscape fire with a meteor storm caused by the break up of a comet, ushering in a prolonged period of cool weather. From what I can ascertain, there was a spike in charcoal at around 13.2 thousand years ago – around 300 years prior to the Younger Dryas event. How can that  happen we might wonder. The key is in the dating methodology. We now have IntCal which uses a variety of proxies – not just C14 and tree rings. For example, it includes speleotherm data [derived from flowstone in caves, an assumption that you can average the rate of dripping in caves,  and the accumulation of calcite]. The result of adding a gaggle of methodologies to the old calebrated C14 methodology and arrive at a more reliable dating system is a matter of faith. IntCal consistently dates events on the calibrated time scale somewhat older than they were just 20 years ago. As an example, the old date of 2350BC for the collapse of EBIII is now dated 2500BC, and the onset of the Piorra Oscillation has risen from 3200 to 3500BC. The IntCal methodology affects all parts of the world – including activity at Stonehenge. However, it has not universally been rolled out. It is not impossible that IntCal methodology has aged the charcoal in sediment cores by 300 years and the landscape fires really do belong to the Younger Dryas boundary event. I’m not betting on that. It is up to the supporters of the latter to counter by re-dating the onset of the Younger Dryas using IntCal, or Bayesian methodology – and see what comes about. But will they?

However, we should bear in mind there was a succession of events that resemble the Younger Dryas in the Late Pleistocene. It should not be all about one event – but about all of them. Many vertebrate species went extinct in the Late Pleistocene – in most regions of the world. An interesting admission as Australian megafauna extinctions are dated much earlier than the disappearance of large herbivores in other parts of the world. However, the article makes clear they are thinking about the last 50,000 years prior to the Holocene, 9500BC. This, in itself, is dating by Bayesian methodology, as previously it was recognised C14 dating could not be done prior to roughly 40,000 years ago. This date coincides with a massive C14 plateau. An injection of cosmic rays that coincided with the Laschamp event. The earth’s magnetic field reversed itself for reasons unknown, bouncing back again several hundred years later. Laschamp coincided with a massive die-off of mammal species – but not their extinction. It also coincided with the disappearance of the Neanderthals. The latter is also bound up with older C14 methodology juxtaposed with newer methodology that has led to the proposition there was an overlap between Neanderthals and modern humans. We might imagine there was a population crash coinciding with Laschamp – just as there was in the wider animal kingdom. The surivors became modern humans, an idea supported by the fact that Neanderthals already possessed a genome closely related to modern humans.

Rancho La Brea, in southern California, provides us with a chance to look at the chronology involved. Naturally occurring asphalt seeps entrapped and preserved the bones of hundreds, and in some cases, thousands, of animals – including massive megafaunal species. However, we come back to the dating problem. No conclusion can really be reached unless the methodology is consistent – right across the board. This led to the researchers dating 192 specimens from the tar pits and the upshot is that they came up with an increase during the Bolling-Allerod period, immediately prior to the Younger Dryas [which is presumably still dated by the older methodology]. So, we have two areas where dates are arrived at in dispute of the idea landscape fires prevailed at the Younger Dryas boundary. The researchers have done nothing wrong as they have used the latest tools in their armoury. However, it is the continuous process of updating and trying to refine the methodology that is confusing the situation. For the scientists as much as the layman.

Skip to content