Water and Oxygen Origins
The oceans go back 4 billion years. With the age of the earth being 4.5 billion years, it means oceans formed early on.
The source of the water in the oceans would have been the oxidation of hydrocarbons. Logic leaves no other alternative.
Until recently, scientists studied the early earth as a reducing environment containing hydrocarbons. (More recent science is unreliable.) There is no other source possible for hydrocarbons than forming as the earth formed. Hydrocarbons forming after the earth formed is an impossibility. Now days, the claim is that breakdown of plant material created hydrocarbons as "fossil fuels." It's totally impossible to convert biological material into hydrocarbons due to the energy state of hydrocarbons being higher than that of biological material, as explained on the fossil fuel page.
Jupiter's largest moon, called Titan, has huge lakes of hydrocarbons, much more than on planet earth. There has never been significant or noticeable biology on Titan. It shows that hydrocarbons were formed without biological materials. A news item describing Titan's hydrocarbons is here: OilPrice Titan News
Most of the volatile hydrocarbons on Earth would have entered the atmosphere and gotten oxidized into water and carbon dioxide creating the oceans and large amounts of CO2. The CO2 combined with calcium in the oceans to form calcium carbonate and limestone.
It means there was a lot of oxygen generated after the earth formed, mostly a half billion years later as the oceans formed. The source of some of the oxygen would have been sodium perchlorate. It breaks down into sodium chloride and oxygen. The large amount of sodium chloride in the oceans points to this mechanism. There is not enough sodium chloride in the oceans for this process, but large amounts of salt are found apart from the oceans in deep layers of salt deposits.
Formation of the oceans would have removed all available oxygen from the environment and still left hydrocarbons buried below the surface. So there was an absence of oxygen until it began to slowly enter the atmosphere 2.5 billion years ago. Scientists are trying to determine if it was rudimentary biological photosynthesis or mineral reactions that produced the oxygen in the atmosphere starting 2.5 billion years ago.
Physicists really screw up geology. They now theorize that water and oxygen were carried to the bottom of the earth's mantle by tectonic activity 2.5 billion years ago. There was no tectonic activity 2.5 billion years ago, because the surface of the earth was a thin crust. Continental plates would all stick together to form supercontinents, until they got so thick that they started to go under and over each other when colliding, which began about 300 million years ago, as indicated by a build-up of CO2.
Conifers evolved 300 million years ago, because hills formed for them to grow on. Nonwoody brush covered the low ground crowding out diverse species of both plants and animals. After hills formed, water washed downward leaving the nonwoody brush not doing well on the slopes. This left the slopes exposed for conifers to evolve on.
It means hills were not developed until 300 million years ago. The reason is because tectonic plates were too thin to buckle when they collided. They just stuck together forming super-continents.
The earth is constantly cooling, as heat moves upward and goes into space. As the earth cools, the crust gets thicker. The crust is now so thick that it buckles during collisions of continental plates, with the layers going over and under each other. This bucking created volcanic activity about 300 million years ago increasing the amount of CO2 in the air. But now the plates are so thick that volcanic magma cannot easily get to the surface, and volcanic activity is at a low level. With oceans absorbing CO2 and volcanoes putting little in the air, the CO2 level is the lowest it has been in measured history.