If Biblical Chronology Goes Back Much Farther Than circa 4000 B. C. Then Where Would Be Gaps in Generations?

Some say that the history laid-out in the Bible goes back tens of thousands even millions of years, but if that were the case, there would be huge gaps in the chronology which though is clearly father to son all the way through, and a flood which covered the earth, Genesis 10 the Table of Nations then following.