Hi anguspure,
That is true, today these creatures have lives of mere moments. Have you any evidence to provide that such was true 6,000 years ago or is it just your assumption that everything works today exactly like it did on the day that God finished his creating and said that everything was very good?
Friend, there are a lot of little minutiae arguments that we can throw out, based on what we see in the world today to deny much of what God has told us. For example, we cannot, based on any evidence that we can provide today believe the story of Jesus' conception. We cannot, based on the very best and finest evidence that we have today, believe that the Red Sea parted and the water stood as a wall on both the right hand and the left hand of the Hebrews. We cannot, based on any evidence available to us today, believe that the sun stood still in the sky or that it was pitch black in all of Egypt for three days while the rest of the world enjoyed fairly normal tours of daylight and nighttime. Finally, we obviously cannot, based on any evidence that we have today believe that God created all of the heavenly bodies within the span of a single rotation of the earth, or that He created all that is, in the span of six such rotations.
So, you can believe what the natural sciences tell you is the truth, or you can believe what God has told you is the truth. That's the choice that we are faced with.
God bless you,
In Christ, ted