Wednesday, April 17, 2019

Exploding Nearby Stars Had An Impact On Life On Earth

When you do radiocarbon dating, you can't just use the results you get from a naive constant decay rate to get a correct date. Instead, you need to calibrate the naively expected date. One of the reasons for that is that there have been times in history when C-14 was artificially increased due to supernovae not far from Earth bombarding our planet with high energy photons.

There have been six such events in the last 15,000 years (twelve other nearby supernovae in the last 50,000 years were still too far away to have a discernible impact).

The fact that we have the ability to use immense volumes of astronomy observations, and a huge global database of calibrated radiocarbon dates, to figure this out is also pretty amazing.
Brief (less than 100 years) rapid-increase anomalies in the Earth's atmospheric radiocarbon production have previously been attributed to either gamma photon radiation from supernovae or to cosmic ray particle radiation from exceptionally large solar flares. Analysis of distances and ages of nearby supernovae remnants, the probable gamma emissions, the predicted Earth incident radiation, and the terrestrial radiocarbon record indicates that supernova causation may be the case
Supernovae include Type Ia white dwarf explosions, Type Ib, c, and II core collapse events, and some types of gamma burst objects. All generate significant pulses of atmospheric radiocarbon depending on distances. 
Surveys of supernova remnants offer a nearly complete accounting for the past 50,000 years. There are 18 events less than or at 1.4 kilo-parsec distance, and brief radiocarbon anomalies with appropriate sizes occurred for each of the closest events. In calendar years before 1950, these are: Vela, 22 per mil del 14C at 12,760; S165, 20 per mil at 7431; Vela Junior, 13 per mil at 2765; HB9, 9 per mil at 5372; Boomerang, 11 per mil at 10,255; and Cygnus Loop (per mil change not calculated) at 14,722. Although uncertainties remain large, the agreements of prediction to observation support a possible causal connection.
G. Robert Brakenridge, "Causation of Late Quaternary Rapid-increase Radiocarbon Anomalies" (April 15, 2019).


NeilB said...

Very interesting! However, aren't there variations in the radio carbon calibration, curve for different regions, e.g. South/North America? Do you know what causes these variations?

andrew said...

Yes. This is certainly not the only reason that calibration is needed. I've understood it better in the past and would have to look it up to say something useful.