The Bible is by far the clearest written history of the world that we have. The Septuagint, the oldest Old Testament that we have complete, says the earth is about 7,500 years old. Josephus (34-101AD) took records from Hebrew OTs, and shows that the earth is about 7,500 years old. | The second sentence in the Bible, right after creation, reads, "Now, the earth was formless and empty." The word 'was' in Hebrew is found translated 'became' all over the OT. This suggests that the earth had been destroyed in its form before the OT first day. | God created light in the first day. Material is made up of electromagnetic particle/waves as is light. This means that either light had been somehow destroyed before the first day, or that the electromagnetic spectrum was different back then. | What this all means is that physics may have been different before the first day, and that there is no way we can appropriately apply the idea of "time." Earth/universe age, totally unknowable.