Where did the water on the Earth come from? After more than 4 billion years, has the amount of water decreased?

If the Earth is compared to a blue marble, then a large part of its luster comes from the ocean.

Seen from space, about 70% of the area of our home planet is covered by blue - liquid water, making the Earth unique in the solar system.

But a natural question then arises: How did this water come about? And over the long more than 4 billion years, have they quietly decreased?

The consensus in the scientific community is that water is not rare in the universe.

Hydrogen is the lightest and most abundant element, and oxygen also ranks among the top three. Once they meet, they can easily combine to form water molecules. In the "primitive nebula" from which the solar system was formed, water exists in the form of ice, vapor, or "crystalline water locked in minerals", etc.

Then, there are mainly two hypotheses about the source of the Earth's water:

First: The exogenous theory - "deliveries" from outer space

When the Sun was first born, the heat it released would cause water in the regions close to it to evaporate, making it difficult for water to exist stably on the surface of planets.

In the early days of the Earth's formation, its mass was not large enough to hold onto the light water vapor. Thus, scientists speculate that much of the Earth's water was delivered at a later time.

These "couriers" might be asteroids or comets.

Especially during the "Late Heavy Bombardment" period from 3.8 to 4.1 billion years ago, the solar system was like a chaotic pinball machine. Countless small celestial bodies crashed into the Earth, delivering the ice and water - containing minerals they carried to the Earth's surface.

Second: The endogenous theory - the Earth was "born with water".

Another view holds that the Earth had a fair amount of water from the very beginning.

Since many minerals in the primitive nebula contained water of crystallization, these substances released water vapor during the collisions and heating processes of the Earth's formation. At that time, the Earth was massive enough to hold these vapors in the atmosphere by gravity. When it cooled down to a certain extent, the earliest oceans were formed.

Modern research has found that both of these claims are supported by evidence. Thus, the mainstream conclusion is that the water on the Earth has both "endogenous" and "exogenous" origins.

Although it may seem that water is safely locked on the Earth, the reality is not that simple.

Although water molecules themselves are relatively heavy and do not escape as easily as hydrogen and helium, water is not always stable.

The Sun's ultraviolet rays can break down water molecules into hydrogen and oxygen - this process is called "photolysis".

The decomposed hydrogen is very light and will escape from the upper atmosphere into space, resulting in irreversible loss.

There is another way of consumption: seawater seeps deep into the Earth's crust and reacts with the hot magma, decomposing into hydrogen and oxygen, and the hydrogen among them may also escape.

Geological and isotope studies indicate that over more than 4 billion years, the volume of the Earth's oceans has decreased by approximately 26% compared to the initial state. That sounds like a significant amount, but this is a figure on the geological time scale - the proportion lost each year is minuscule, and humans can hardly feel it.

Why can water still maintain a balance?

Fortunately, the Earth's atmosphere now contains about 21% oxygen, which means that even if hydrogen is released, there is a chance for it to recombine into water with the participation of oxygen.

In addition, during the Earth's revolution, it will still occasionally capture small ice blocks, asteroids, and hydrogen - containing dust from space, adding a little to the "inventory" of the water reservoir.

Overall, the Earth's water is currently in a state of dynamic equilibrium: there is loss, but also replenishment. Scientists predict that there will be no significant water shortage problem on Earth within the next billion years. What may truly threaten water resources is not astronomical evolution, but human consumption and pollution.

Conclusion

The water on Earth is like a traveler who has weathered billions of years. Some of it came from the embrace of minerals native to the planet, while some journeyed across the stars from distant icy regions.

These waters have witnessed the transformation of the Earth from a searing ball of rock into a blue planet. All the while, they have been silently and slowly losing a part of themselves.

The oceans we can see today are not only a gift from the universe but also the result of the Earth's long - term guardianship.

It reminds us that cherishing every drop of water is not just about conserving resources but also about respecting this 4 - billion - year - long interstellar story.