EARTH - TWO-THIRD OCEANS

 Why is the Earth two-third oceans?

There is no definitive answer.

First, how did the Earth get its water?

There are two main theories: one is that the water came from inside the Earth, and the other is that it came from outside the Earth.

The first theory says that when the Earth was forming, it had a lot of water trapped in its rocks and minerals.

As the Earth heated up and melted, some of this water escaped to the surface and formed oceans.

The second theory says that the water came from comets and asteroids that crashed into the Earth.

These space rocks had ice on them, and when they hit the Earth, they melted and released water.

Both theories are probably partially correct.

Scientists think that both sources contributed to the Earth's water supply, but they don't know exactly how much each one did.

It's possible that the ratio changed over time, depending on how many comets and asteroids hit the Earth.

See, the Earth's water cycle is not a closed system. That means that water can be added or removed from the planet in various ways:

Volcanic eruptions

Volcanoes can spew out water vapor and other gases into the atmosphere, which can then condense and fall as rain or snow.

Subduction

This is when one tectonic plate slides under another and sinks into the mantle.

When this happens, some of the water in the ocean crust gets dragged down with it and recycled into the mantle.

Space weathering

This is when solar wind and cosmic rays hit the surface of the Earth and break down water molecules into hydrogen and oxygen atoms.

Some of these atoms can escape into space, especially hydrogen, which is very light.

So back to your question.

It's hard to say for sure.

Some estimates say that the Earth has lost about 25% of its original water since it formed, while others say that it has gained about 10%.

It's possible that the amount of water has fluctuated over time, depending on how active the volcanoes, subduction zones, and space weathering were.

So what does this all mean for the question of whether the Earth has always been two-thirds ocean?

There is no definitive answer.

The Earth's surface water content and distribution have changed over time, and they will continue to change in the future.