Below the Paired Spaces (Under the Heavens)
The phrase "under the heavens" is what we today would call Planet Earth. The 'earth' that God created on Day one is often misinterpreted as Planet Earth because that is its most common meaning today. However, the Hebrew word 'erets' rarely, if ever, means Planet Earth. It is most often translated as 'land'. It is the 'land' of Israel, the 'land' of Syria, the 'land' of Babylon, the 'land' of Egypt, etc.
The third day is when God took material earth left under the heavens and formed it into Planet Earth. He then separated the dry land from the waters and called to the land to produce plants in abundance.
God Defined 'Soil' and 'Seas'
These are the last two, of five, words that God defined in the creation account. In every definition he gave the most common meaning of the word. He defined 'soil' (earth, Hebrew 'erets') as the dry ground. That is its common meaning today -- the land. He defined the gathered waters as seas (oceans). Again this is the normal meaning. Why does God need to define these words if He is using the common meaning?
God defined these words to help us understand that from here on, the words take on their normal meaning. However, in previous verses the meaning is not exactly the same.
In other words the soil/earth material of Genesis 1:1 is like land in that everything comes from the land (food, building material, metals, animals, etc.). However, the initial 'soil' was formless and completely dark. Perhaps it was not even in atomic structure yet. God used this 'soil' to produce every physical thing in the universe (Planet Earth, sun, moon, stars, plants, animals, etc.).
Similarly, the waters at this point are normal waters. However, the waters on day one were not anything that God would call an ocean. Instead, they were completely dark and formless. Anything in atomic structure produces light (electro magnetic radiation). A human body produces about as much light as a 100 watt light bulb. However, it is not of a frequency our eyes can see -- unless we use night vision goggles. The water on day one was completely dark -- no electro magentic radiation. It could not be like any water we know today.
Furthermore, the way the term 'waters' was used in Day one was as an adjective describing the earth material. The earth material was watery or liquid. That is why Isaiah (44:24 and 42:5) described the second day as the spreading out of the earth rather than the spreading out of the waters as Genesis described it.
For us to understand the Creation Account, God used words we understand to describe conditions that we have never seen and would not understand. Now, by the third day things are becoming sufficiently 'normal' that these words can take on their normal meaning. God defined these words with their common meaning to help us understand that prior usages of these words do not have the normal meaning.
Plant Families and Species