I believe in animal evolution to a certain extent but believe God's hand was in it at certain stages.
Where do you have reservations? The evidence for human evolution is absolutely solid. The same techiques that we use to convict murderers and rapists also proves that humans shared a common ancestor with all other living things millions of years ago.
Please see The Common Ancestry thread for details...
How does adding god to the process help in any way?
It's as if man's growth was stagnant for 490,000 years and then took off in the last few thousand years.
Modern humans have been around for about half that time you suggest. Populations grew slowly for lots of reasons that have been given in this thread already. There would be many occasions when disaster would have decimated populations as well.
wouldn't you have to be sure that the atmosphere now is the same as it was when the object you are looking at first appeared/died?
No that's not how it works at all. It is not necessary to make any assumptions for radiometric dating to work accurately. Multiple independent clocks all point to the very same dates. We know the age of the earth from many lines of evidence.