And God said, “The waters shall swarm with swarms of living creatures, and let birds fly above the earth across the expanse of the heavens.” 21So God created the great sea creatures and every living creature that moves, with which the waters swarm, according to their kinds, and every winged bird according to its kind. And God saw that it was good. 22And God blessed them, saying, “Be fruitful and multiply and fill the waters in the seas! And, let birds come to multiply on the earth.” 23Then there was evening and there was morning, the fifth day. –Genesis 1:20-23
I have my own personal interpretation of this passage that may not fit with traditional old-earth views, but I have some reasons for why I believe what I do.
First, it is clear that the bird formation comes after the marine life formation. Three times the birds are mentioned after the filling of the seas with creatures. This is a clear indication of the order in which this happened.
Next, there is no phrase that says, “It came to be so.” This indicates, to me, that the formation of the birds was not complete, or was perhaps hardly begun, during Day 5.
Also, I note that the focus for the marine life is that the waters “swarm with swarms of living creatures.” The birds are not said to fill the skies, but the marine life is said to “swarm” and to “fill the waters in the seas.” Therefore, as a result, I suspect that this is not talking about the fish and other sea animals first coming to exist, but a time when they flourished in the oceans and modern marine life was formed (v. 21). It’s also a time when birds soon after came to multiply on the earth.
So, does the fossil record have such a time when marine life exploded with modern kinds of animals and birds shortly started being formed and multiplying? Yes, indeed. Around 251 Ma, there was a massive extinction event that killed off about 95-97% of all marine species. Few of the modern types of marine animals were survivors of this extinction event. In other words, almost all modern kinds of marine life exploded in the oceans after 251 Ma. It is from this point that about 96-97% of all the marine life came into being.
Also, as the marine animals were filling the oceans, birds started being formed around 160 Ma. Most of the basic bird kinds had been formed by c. 70 Ma, according to the fossil record. Modern mammals, however, were almost nonexistent at 70 Ma.
So, once again, established science seems to fit with Genesis 1. The marine life exploded and the waters did indeed “swarm with swarms of living creatures” and birds did come to “fly above the earth” during 251-80 Ma, and this was clearly after plants had multiplied on the earth and many kinds of plants and trees had formed, just as Genesis 1 says happened on Day 3.
I want you to notice that I am making full use of all the words in Genesis 1. The young-earth view doesn’t truly make use of all the words and the order of events.