It's not that the earth is 10,000 years old; rather, god created humans at some point within the last 10,000 years.
The difference is huge. This, however, cannot be interpreted in any other way:
Let's assume god indeed *chuckle* did create humanity 10,000 years ago. god also created the universe and everything else in seven days; on the sixth day god created man.
So... 47% of Americans actually believe the universe was created within the last 60,000 years (since god rested on the seventh day).
I'm not a religious person at all, but my god...