This is incorrect. First of all, the Bible does not say that God made the world in seven days and rested on the eighth. It says he made it in six days and rested on the seventh.

Secondly, there bloodline in Genesis is not necessarily without gaps. You have to understand the ancient mindset as well as the language in which the bloodline was recorded. Most ancient genealogies have gaps in them. Many read like the bloodline in Genesis. The word "son" or "begat" does not literally mean "son" as we take to today (not in the original language and not by the understanding of the ones that wrote it). The word "son" ("ben" or "bar" in Hebrew) showed a decent or a genealogical connection. It did not necessarily mean that there was a father/son relationship. It could mean one was the grandfather or even a great-great grandfather. But it did show direct decent. The term "begat" (in the original language) did the same thing.

In many ancient genealogies there were gaps. The authors often left out people that just were not considered important enough to include. Others were included only to show decent. The ancient mindset was not as concerned (historically) with getting every little detail correct and in chronological order. Thinking like this is fairly recent.

In any case, most creationists claim the earth (and all of creation) could be up to 20,000 years old and not just 6,000+. Again, I am not saying I agree with this, but if someone wants to point out a Bible contradiction then they need to try to find a legitimate one and not harp on things like this.