) and they are historically the ones posted to talk.origins more than any others.
Helium is not light enough to escape the Earth's gravity (unlike hydrogen), and it will therefore accumulate over time.
The current level of helium in the atmosphere would accumulate in less than two hundred thousand years, therefore the Earth is young.
Further, the processes of erosion and crustal recycling have apparently destroyed all of the earliest surface.
The oldest rocks which have been found so far (on the Earth) date to about 3.8 to 3.9 billion years ago (by several radiometric dating methods).
For example: Also note that the meteorite ages (both when dated mainly by Rb-Sr dating in groups, and by multiple means individually) are in exact agreement with the solar system "model lead age" produced earlier.
Young-Earthers have several methods which they claim to give "upper limits" to the age of the Earth, much lower than the age calculated above (usually in the thousands of years).The higher the uranium-to-lead ratio of a rock, the more the Pb-206/Pb-204 and Pb-207/Pb-204 values will change with time.If the source of the solar system was also uniformly distributed with respect to uranium isotope ratios, then the data points will always fall on a single line.(I believe this argument was originally put forth by Mormon young-Earther Melvin Cook, in a letter to the editor which was published in .) But helium can and does escape from the atmosphere, at rates calculated to be nearly identical to rates of production.In order to obtain a young age from their calculations, young-Earthers handwave away mechanisms by which helium can escape.Those which appear the most frequently in talk.origins are reproduced below: Note that these aren't necessarily the "best" or most difficult to refute of young-Earth arguments.