Late intense bombing
Question: Where did all the water on Earth come from?

Hypothesis
Part of it arrived with the intense late bombardment (majorly indirect), part of it accumulated inside the planet during its growth from a grape of dust to a planet, and part, perhaps, is due to thermochemical reactions inside the planet.

Ice between the rocks
Most of the water is probably contained on the planet itself: we must consider the "ice" that the future Earth assimilated during its growth. As close-up studies of comets and asteroids seem to show, during their growth phase, rocky objects accumulate a lot of water in the form of ice, which has the capacity to bond and retain dust and debris. Little by little, this ice-rich surface layer was covered by other space material and became buried deeper and deeper within the asteroid. Starting from a grain of dust or a small stone, the Earth grown by assimilating rock, gas, and above all, a lot of ice (one of the most common molecules in space). It took the planet a long time to gain enough mass to generate the pressure needed to ignite its iron core. In the meantime, it incorporated large quantities of ice into its rocks, and only after the core ignited did the heat push it to the surface, creating the oceans. Obviously, the amount of water remaining trapped between the rocks of our planet depends on two factors that are difficult to estimate: the amount of water in the primordial cloud and the time available for it to grow.

Thermochemical reactions (perhaps)
During its growth, the Earth assimilated not only water molecules, but also oxygen atoms bound by other elements of the Earth and free hydrogen atoms. Between minus 253 and minus 259 degrees Celsius, hydrogen behaves like a water/ice fluid, adhesives to dust and rocks, remaining physically trapped. That being said, is it possible to hypothesis that, as the planet growth, the pressure and heat were sufficient to strip single hydrogen and oxygen atoms from the molecules that make up the rocks and force them to combine into completely new water molecules, with atoms of space origin but with an earthly chemical composition? Could this explain the different deuterium percentages?

Intense direct and indirect late bombardment
The theory suggests that most of the water on Earth came from space, carried by comets and meteorites. This event could have brought water to Earth in two different paths. The first, which we could call "direct" bombardment; as the name suggests, consisted of the direct impact of thousands of asteroids and comets launched into Earth, perhaps due to Jupiter's approach, which released their water contents. However, perhaps, the main water contribution came from what we could call "indirect" bombardment. The center of the target is the Sun; of all the objects that have headed toward the center of the solar system from all directions, only a small fraction have hit the rocky planets. Most of the objects headed toward the Sun undisturbed but failed to reach it because they were disintegrated by heat and gravity; each object was transformed into a cloud of gas and dust that was then blown away by the solar wind. This very light cloud slowly dispersed, giving the rocky planets time to capture it during their orbits around the Sun. In conclusion, rather than "bombardment," we should speak of "debris collection." Most of the asteroid and comet material that the Earth has absorbed probably derived not from direct impact, but from objects that were vaporized by the Sun, dispersed by the solar wind, and collected during their orbits around the Sun. Could this process explain the different deuterium content between water on Earth and water in atheroids? Could the combined effect of vaporization by the Sun and the action of the solar wind have created the different percentages of deuterium between water on Earth and that in space?

The idea of "indirect" bombing provides further considerations. It can give us a different image of the Earth's Earth: it was not a fireball. Until now, based on the idea of direct impacts, it has been calculated that an extremely high number of asteroids and meteorites was necessary to bring all the water currently present on the planet. Each impact releases a lot of energy, and this high number has always lead to the hypothesis that the Earth's surface was molten rock. However, "indirect" bombardment brought water to the planet without impact, therefore the number estimated so far must be reduced, and perhaps the surface was not as hot as hypothesed. Indeed, perhaps, this “space debris” made of gas, dust and ice, when they enter the atmosphere, turn into rain, helping to cool the planet. Even before the possible impact with Theia, it was always assumed that the Earth was a ball of molten rock because accretion was viewed as a violent process, based on impacts between objects. However, we know that in space, gas and dust are more widespread and have a greater mass than larger objects, so it is plausible to assume that most of the Earth's mass was formed by the accumulation of gas and dust rather than by impacts with space rocks.

These considerations imply that the environment was more favorable for the birth of life, which had more time to develop than have been hypothesed so far. Indirect bombing may also help explain Venus's enormous greenhouse effect. It is possible that before the bombardment, Venus had liquid water on its surface, volcanic activity, and environmental conditions similar to those on Earth. Just as on Earth, a balance was slowly being created between volcanic activity, greenhouse gases, and other environmental conditions, it is plausible to hypothesize that during the bombardment, it intercepted a large quantity of gases and dust that remained suspended in the atmosphere because the planet was unable to absorb it. Venus was cooling more slowly than Earth, also due to its proximity to the Sun, and any aquatic organisms and vegetation did not have time to develop enough to absorb all the water coming from outside. Space dust also had difficulty settling due to the shortage of rain.

Further consideration
Are there still traces of asteroids? After millions of years of continuously mixed molten lava, why is the chemical composition of the crust so uneven? Why does lava from volcanoes have different concentrations of elements such as sulfur, iron, or carbon?

Hypothesis
The lava of some volcanoes is partly formed by the remains of meteorites or comets that arrived during the intense late bombardment. According to the impact theory, after the Moon's formation, the Earth was a ball of glowing rock; comets were vaporized, meteorites molten on contact, and all the elements are continuously mixed by convection. Little by little, the surface cools and the Earth's present crust formed; meteorites stop melting completely, leaving ever larger and intact blocks of rock on the surface, which become part of the present crust. In all volcanoes, the lava and ash that emerge are mostly made of rocks belonging to the crust, melted inside the magmatic chambers, and present the elements distributed in different quantities; theoretically, only the mantle is formed of rocks from the primordial Earth, while the solidified surface layer, the Earth's present crust, is however contaminated by extraterrestrial material from comets and meteorites. Perhaps only by analyzing the Kilawea lava, the only point from which material coming directly from the mantle emerges, will we find an average, constant and homogeneous distribution of all the elements of the periodic table. In conclusion, is it possible that some volcanoes erupted residual material from the late bombing? This could also explain why some elements are concentrated in deposits and mines; for example, in Sudbury, Canada, there is a mine of a very particular type of coal, which extends in an area so confined that it might be the remains of a meteorite. Plates and faults have mixed the rocks of the crust and the elements of the tablet, but, perhaps, in the most ancient points of the crust there are still entire mountains that seem out of place with the surrounding geology.