What does the Bible mean by "in the waters under the earth" ? What is found in the waters under the earth? Fish, gold, silver, and other creatures and precious stones, metals, and minerals in the waters under the earth?
In the creation account of Genesis 1, God created the firmament to divide the waters. Following this, they are divided into the waters under the firmament, named "Heaven," and the waters which were above the firmament.
And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters. (Genesis 1:6, KJV)
And God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament: and it was so. (Genesis 1:7, KJV)
And God called the firmament Heaven. And the evening and the morning were the second day. (Genesis 1:8, KJV)
And God said, Let the waters under the heaven be gathered together unto one place, and let the dry land appear: and it was so. (Genesis 1:9, KJV)
And God called the dry land Earth; and the gathering together of the waters called he Seas: and God saw that it was good. (Genesis 1:10, KJV)
In the Ten Commandments, these waters which were under the firmament, and which had been separated from the dry land (Earth), are also said to be "under the earth."
Thou shalt not make unto thee any graven image, or any likeness of any thing that is in heaven above, or that is in the earth beneath, or that is in the water under the earth. (Exodus 20:4, KJV)
For in six days the LORD made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the LORD blessed the sabbath day, and hallowed it. (Exodus 20:11, KJV)
These waters, then, were those that included all of the sea life that God had created on the fifth day of creation.
NOTE: The waters are below the level of the land, which is why they do not overflow the land. In this sense, they are truly "under" the earth. The Hebrew word here could also be translated as "beneath."
The fish, whales, and other sea life that God created in the sea are those things which are in the "waters under the earth."
The Bible informs us that the pre-flood environment was different from what we experience today. Between the waters on the surface of the earth and the waters above, there was an expanse (Genesis 1:6-7). Genesis 2:6 says that a mist went up from the land and this watered the whole face of the ground.
During the lifetime of Noah and his family, there was a global flood, and Genesis 7:11 tells us where the water came from:
In the six hundredth year of Noah’s life, on the seventeenth day of the second month – on that day all the springs of the great deep burst forth and the floodgates of the heavens were opened.
This suggests that great quantities of water came from below the earth as well as from above. Although the Bible does not tell us any more about the waters that were below the surface of the earth, science does. One view is that there may be an underground ocean three times greater than what we see on the surface of the earth.
Some scientists think Earth's oceans formed when icy comets hit the planet. But new research suggests a different origin for the oceans: they simply seeped out of the center of the Earth. The finding, published in Science, suggests that a reservoir of water is hidden in the Earth's mantle, more than 400 miles below the surface. Try to refrain from imagining expanses of underground seas: all this water, three times the volume of water on the surface, is trapped inside rocks. https://ssec.si.edu/stemvisions-blog/there-ocean-below-your-feet
This 2020 article suggests that he water stored in the inner layers of Earth may be more plentiful — and important — than scientists previously thought.
Under the extreme temperatures and pressures existing far underground, water breaks down into its constituent elements, hydrogen and oxygen, which are chemically bound to the rock’s crystal structure. But to geophysicists, it’s still water, regardless of the form it takes. This begs the question: How much of this water is buried beneath the surface? The answer could help explain our planet’s suitability for life and tell us how all this water got here in the first place. Source: https://www.discovermagazine.com/planet-earth/the-search-for-earths-underground-oceans
To answer your question, what does the Bible mean by "in the waters under the earth", the Bible is not specific. However science indicates that there are no “seas” that contain fish or other living creatures. The water may contain traces of minerals, metals and diamonds, but not in a form that could be extracted and instantly recognised.
We do not need to know the details. After all, the Genesis account of creation and the flood is not meant to be a scientific paper. Rather than looking into the bowels of the earth, we do better to lift our eyes to heaven to the creator of time, space, matter and all life and give Him our thanks.
P.S. Jesus Christ believed in the universal flood and took it as the type of the coming destruction of the world when He returns (Matthew 24:37-39; Luke 17:26-27). Hebrews 11:7 also refers to the flood during the time of Noah.
The phrase "in the waters under the earth" is used in context of forbidding idol worship and making graven images for idol worship. In addition to the prohibition of Ex. 20:4 we find -
"16 lest ye do corruptly, and have made to you a graven image, a similitude of any figure, a form of male or female --
17 a form of any beast which [is] in the earth -- a form of any winged bird which flieth in the heavens --
18 a form of any creeping thing on the ground -- a form of any fish which [is] in the waters under the earth; (Deu. 4:16-18, YLT)
"`Thou dost not make to thee a graven image, any similitude which [is] in the heavens above, and which [is] in the earth beneath, and which [is] in the waters under the earth;" (Deu. 5:8, YLT)
Therefore, as they were forbidden to make graven images of either men or women, or any creature or object they could see in the heavens above, or in the waters under the earth, then the context has to include the objects or creatures they could see in the waters under the earth, ie: whales, fish, corals, dolphins, starfish, eels, etc.
We do know that some forms of life have become extinct due either to Noah's flood, or to excessive hunting by mankind, so some of the creatures that may have appeared very large or fearsome as to inspire awe are no longer with us. But, the context was concerning making images of things they could see.
The implication of "the waters under the earth" is very interesting when examined more thoroughly. If interested you might read my post "Is the Earth Hanging Upon Nothing>" here: ShreddingTheVeil