(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.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).While these values do not compute an age for the Earth, they do establish a lower limit (the Earth must be at least as old as any formation on it).This lower limit is at least concordant with the independently derived figure of 4.55 billion years for the Earth's actual age.) and they are historically the ones posted to talk.origins more than any others.
However, the test for these assumptions is the plot of the data itself.
Some of these rocks are sedimentary, and include minerals which are themselves as old as 4.1 to 4.2 billion years.
Rocks of this age are relatively rare, however rocks that are at least 3.5 billion years in age have been found on North America, Greenland, Australia, Africa, and Asia.
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.