Gerald Schroeder is part scientist and part theologian and wrote a book called, "Genesis and the Big Bang".
His science background is physics and his theological background is Judaism.
As a result, he cannot adopt the young earth creationism because it is contradictory to what he knows to be science, yet he will not throw away the Genesis account because of his knowledge of Judaism.
The general gist is, he studied rabbinical commentary on Genesis, ancient commentary that is pre-modern science. In it, he discovers a wondrous thing, the ancient rabbinical commentary think that the era of creation was much longer than 6 days.
The issue seems to be the King James version vs. the original Torah in Hebrew. There have been bad translations that led one to think, reading the KJV, that creation was only 6 days.
Add to this his own theory of the 6 days of creation, the theory being that the 6 days of creation are really describing the 15 billion or so years of the age of the universe. In short, with each day of creation time halves. That means that the first day is 4 billion years, day 2 is 2 billion years, etc. The interesting thing is, if you use his calendar it matches the scientific calendar for such things as the creation of the stars and the Cambrian Explosion in the seas, etc.