There are several conflicts in this verse that skeptics have in their understanding of this verse. The first is firmament being meant as a hard dome surface but we see in the following verses that birds fly in the firmament which would be impossible to do in a hard domed surface. The second is that the sun was formed first with the moon and earth thereafter.
My viewpoint is that the age of the earth is not conclusive due to plate tectonics, the oldest known rocks are probably lost to us and those that are in evidence show the earth much older than scientists first believed. 03 February, 1998. Astronomers have been able to date the Sun by applying the theory of stellar structure and evolution to data that describe the interior of the Sun found through the study of solar oscillations. The Sun is dated at 4.5 billion years old, satisfyingly close to the 4.56 billion year age of the Solar System as found from the study of meteorites.
http://solar-center.stanford.edu/FAQ/Qage.html
Dating the Sun is an indirect process. There are several independent ways of estimating the age and they all give nearly the same answer: about 5 billion years.
The age of the Sun can be estimated from the ages obtained from radioactive dating of the oldest meteorites. This may seem odd at first, but in fact it is extremely likely that the solar system (i.e. th Sun, planets, asteroids etc.) formed as one unit. Therefore the age of the Sun should be close to the age of the meteorites, which can be found using the method of radioactive dating.
G.J. Wasserburg obtained a meteoritic age of (4.57 +/- 0.01) x 10^9 years and D.B. Guenther (1989, Astrophysical Journal 339, 1156) estimated that hydrogen burning started shortly thereafer (40 million (0.04 +/- .01) x 10^9 years later).
Additional evidence comes from the Earth. The oldest Earth rocks are also about 4.6 billion years old. The oldest fossils, found in Australia, are about 3.5 bilion years old. The presence of fossils in rocks indicates that the Earth was a suitable place for life when the fossils formed. This implies that the Sun was luminous at that time. [Of course we can't say exactly how long before the fossil formed the Sun was like it is today, but it does give us a lower bound.]
What is meant by "luminous?" We mean that the Sun was at or near the stable part of its lifetime called the "main sequence" more than 3.6 billion years ago. Viewing the Sun as a star on the main sequence, is very useful and important for astronomers because they have a model called "The Standard Solar Model" that views the Sun at stages in its life while it is burning hydrogen and converting that to helium. The model can be run forward and backward in time, and the astronomers can check the observable quantities in the model like luminosity, solar radius, composition, solar p-mode frequencies, and so on with our real Sun. They can stop the model at any time during its main sequence. If what we see from our Sun matches the quantities in the model for a specific age, then we have one more piece of information of what we think that the age of the Sun is.
One complication of checking the Solar Model with our real Sun is the quantity of helium: the "helium abundance." That is rather difficult to obtain. According to the Dalsgaard article (see below), the solar spectrum is too complicated to accurately measure the helium abundance, so that one parameter has to be estimated (one infers the helium abundance by matching the observed solar radius and luminosity in the solar models). It turns out this affects the estimated age very little.
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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.