I have always wondered if the different isotopes were simply deposited at the same time and had very little to do with true age.

Y.E. Creationists will be gloating!

So, is it off by millions of years or billions of years or are they at least in the universal ballpark.

I made this same argument (other, perhaps even unknown, variables) to my high school science teacher... way back in 1972. He told me I was an idiot, and that the science of radioisotope dating was settled.
Oops.

Hmmmm....if the facts don't fit the theory, change the facts.

Mistakes aside, the age of rocks are STILL MUCH OLDER than the outrageous 12 Thousands years maximum posited by the deluded 'young earth' silly people.
Religion comforts...and cripples. History is quite clear on the matter.

Aha! Take that Science! The Earth is 5000 years old! /notseriousatall

Radioisotope dating is not the only option, and any scientist exercising due diligence will use a number of methods. For example Potassium-Argon dating does not rely on assumptions of the initial distribution of the two elements as any Argon present in the molten rocks will bubble out leaving just Potassium present. Any Argon subsequently found to be present will be there due to Potassium decaying into Argon. Thus from our knowledge of the half-life of Potassium and the ratio between the two can give us a good estimate of the time since the rock crystallised.

'...our understanding of Earth's ancient timeline could be worryingly inaccurate....'. No surprise here. I am sure the earth is many millions of years old, possibly hundreds of millions. Or even billions. I am not sure. But I do know that we most likely are wrong by a pretty wide margin. It's just a shame I won't be around in 200 years or when we figure it out. So that I can laugh at 2017-man for his misunderstandings!

*yawn* It's not like I believed this "millions of years" foolishness to begin with.