In verse twelve we see many kinds of plants growing.  “And the earth brought forth grass, (genetically specific) and herb yielding seed after his kind, (genetically specific) and the tree yielding fruit, whose seed was in itself, after his kind…” (genetically specific). 

Three days have passed.  That is…three rotations of the earth have occurred.  Who knows how long a rotation took?  If you believe the earth has always had days that were twenty-four hours long, you are misled.  Rotation speed sometimes changes when there is a large earthquake, an asteroid impact, etc.  Rotation speed can change.   It has in my lifetime.

The next verses, on Day Four, are not very clear.  Genesis 1:13-19 says, “…Let there be lights in the firmament of the heaven, and let them be for signs and for seasons and for days and years…let them be for lights in…the heaven to give light upon the earth:  and it was so.  And God made two great lights; the greater light to rule the day, and the lesser light to rule the night: he made the stars also…to divide the light from the darkness…”

These verses in some ways seem to be partly repetitive, perhaps an explanation of the arranging, or giving purpose to different lights--since the sun was already shining; the sun had already been busy growing seeds into plants back on day three.  God had already created the "heavens" back in verse one.