Too old dating
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.
) and they are historically the ones posted to talk.origins more than any others.
The young-Earth argument goes something like this: helium-4 is created by radioactive decay (alpha particles are helium nuclei) and is constantly added to the atmosphere.
This involves measurement of three isotopes of lead (Pb-206, Pb-207, and either Pb-208 or Pb-204).
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.
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.
However, they are quite popular in modern creation-"science" literature (even though they should not be!