20 And God said: 'Let the waters swarm with swarms of living creatures, and let fowl fly above the earth in the open firmament of heaven.'
This is stating what God wants done and the next verse says that is what he did.
21 And God created the great sea-monsters, and every living creature that creepeth, wherewith the waters swarmed, after its kind, and every winged fowl after its kind; and God saw that it was good.
The Cambrian era was the time period which consisted of all phyla alive today and some that have gone extinct. The waters literally swarmed with life. This period which is called the Paleozoic period includes the Silurian era in which there were centipedes and millipedes, the Devonian with its sharks and amphibians. This also includes the next period which is the Mesozoic period which then includes dino's and of course within this period comes the first appearance of birds. This is a general overview of what was created during this period. So an overview of this is that the day includes first the Paleozoic and next the Mesozoic.
24 And God said: 'Let the earth bring forth the living creature after its kind, cattle, and creeping thing, and beast of the earth after its kind.' And it was so. 25 And God made the beast of the earth after its kind, and the cattle after their kind, and every thing that creepeth upon the ground after its kind; and God saw that it was good.
Now life moves to land. This is describing the Cenozoic period. The first mammals appear during this period.
26 And God said: 'Let us make man in our image, after our likeness; and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing that creepeth upon the earth.' 27 And God created man in His own image, in the image of God created He him; male and female created He them. 28 And God blessed them; and God said unto them: 'Be fruitful, and multiply, and replenish the earth, and subdue it; and have dominion over the fish of the sea, and over the fowl of the air, and over every living thing that creepeth upon the earth.' 29 And God said: 'Behold, I have given you every herb yielding seed, which is upon the face of all the earth, and every tree, in which is the fruit of a tree yielding seed--to you it shall be for food; 30 and to every beast of the earth, and to every fowl of the air, and to every thing that creepeth upon the earth, wherein there is a living soul, [I have given] every green herb for food.' And it was so. 31 And God saw every thing that He had made, and, behold, it was very good. And there was evening and there was morning, the sixth day. http://mediatheek.thinkquest.nl/~ll125/en/life-3.htm
The Cenozoic is the most current era, taking place from the last mass extinction of all land-based dinosaurs (approximately 65 million years ago) to the present day.
This era saw the rise of many mammals, such as whales, the great hunter cats, as well as Humans. But it also saw the rise of the birds, insects, and many new plants, including flowering plants.
Much of life as we know it today evolved during this era.
So we have in the general overview:
1. The Hadean, the Archeozoic and the Proterozioc eras.
2. The Paleozoic
3. The Mesozoic
4. The Cenozoic
All wrapped up in the Genesis narrative.