I think, therefore, I am

Does this mean that atheists can at the very least know that they exist without presupposing the God of Scripture? No.

Consider, that Descartes is actually begging the question. In order to prove your own existence, you cannot start with yourself as that would be circular reasoning.

The correct start to the argument would rather be something like "There is thinking.." but then you'd have a hard time to prove the "I" from there.

To quote Bahnsen, this argument is like saying:

"More like I stink therefore I am..."

Or also,

"More like, I beg the question therefore I am."

The correct form of the argument would rather be:

God is, therefore, I am.