World's Oldest Human Footprints

Gorbie writes "An article on Yahoo tells about the discovery of 350,000 year old human footprints found in Italy."

Re:How old are they?

[Anonymous Coward]

whole rock K-Ar dating on rocks only 10 years old is NEVER going to give you interpretable results.

1) whole rock dating is, as it sounds, dating a rock without regard to the specific mineral phases within it. this is a major point because different minerals have different diffusivities (and therefore closure temperatures) with respect to loss of radiogenic 40Ar.

2) K-Ar dating, while useful, gives results with large uncertainties. for example, a 10 million year old K-Ar date typically has uncertainties on the order of 1-2 million years. with more modern 40Ar/39Ar dating (a variant of K-Ar dating), those uncertanites are more like 0.1 to 0.5 million years.

3) THE SAMPLES ARE ONLY 10 YEARS OLD!!!! that is (by a long shot) not enough time to accumulate radiogenic 40Ar in the sample. the half-life of 40K is just too damn long and given the state of the art in mass spectrometry, there is no way to get a high enough signal to noise (e.g. count enough 40Ar atoms) to calcualate an age (let alone a reliable one). even if you analyze tens of kilograms of sample (which is not practical).

what were the uncertainties of mr. austin's K-Ar dates? geochronologic results without uncertainties are useless.

i hear this crap argument about 10 year old mt. st. helens rocks being dated as hundreds of thousands of years old all the time. it's a load. first (as i discussed above) you can't expect to be able to date a rock that young anyway (at least not with K-Ar, 40Ar/39Ar or any other common isotopic system).

second, this argument takes no account of the geologic context of the samples austin dated. are they indeed volcanic rocks that cooled from a magma 10 years prior to their collection? or were they much older rocks that were blown out of the volcano in the recent eruption. rocks that crystallized from a lava not 10 years prior, but, rather in a much older eruption. say 300 thousand years ago?

>Radiometric dating is not science, since given known-age rocks, the best labs around return wildly wrong results.

you have no clue what you are talking about.

Re:How old are they?

[fluffy666]

But given that K-Ar dating is typically used for age ranges in the 10s or 100s of millions of years, these results show that the uncertanty due to primordial argon is small, and hence the method is accurate. Thanks for demonstrating that radiometric dating is reliable.