Earth is a planet full of liquid water, with about 71% of its surface area covered by seawater, and this number is getting bigger as sea levels rise as global warming increases.
Many people may have wondered what the bottom of the sea looks like. The simple answer is that it is almost the same as the land. There are mountains, canyons, and plains, but they are all in lower places.
But still no one can fully map the underwater world, because the satellite radar technology we use to map land topography doesn’t work well in water.
In fact, maps of the moon, and even Mars, are now clearer and more reliable than maps of Earth’s oceans, because oceans are more difficult to explore than the moon and Mars.
Although the underwater world still leaves us with a lot of fantasies, the more magical place is, why only the earth has oceans, and where does the earth’s massive water resources come from?
How does water on earth come from?
Although the earth is filled with liquid water everywhere, compared to the composition of the entire earth, all the water resources on the earth’s surface – including the total volume of frozen, evaporative, and liquid water, are only about the existing volume of the earth. one thousandth of .
Most of the water resources are in the ocean, accounting for about 96.5% of all the water resources on the earth. Only about 3.5% of the earth is freshwater, and about 68% of the freshwater is in glaciers, so save water, freshwater resources are indeed quite nervous.
The reason why sea water is salty is that it is influenced by the earth’s plate tectonics, which is caused by the mixing of liquid water with the material inside the earth.
In other words, most of the earth’s water resources are actually “polluted”, which brings a lot of trouble to the source of the earth’s water resources.
Now, there are three main hypotheses about the source of water resources on the earth. The first is that the earth collected water resources together during the initial accretion of its formation; the second is that some water-rich meteorites gradually formed during and after the formation of the earth. Sending water resources to the earth, these meteorites may be similar to the carbonaceous chondrites we can still see today; the third is also from late growth, but some icy asteroids, which are comets we see now, Gradually deliver water to the earth.
If one wants to know the correct source of Earth’s water resources, one must understand the present and past composition of Earth’s water resources, as well as the composition of meteorite and comet water resources.
Carbonaceous chondrites, credit: Mario Müller
First of all, it is certainly impossible for meteorites to transport too much of the earth’s water resources.
That’s because carbonaceous chondrites are basically rich in xenon—a noble gas that’s rarely found on Earth today, so most people probably haven’t heard of it.
In fact, if one of the main sources of Earth’s water resources included meteorites, the xenon content of Earth’s atmosphere would be at least 10 times higher than it is today.
Image: Halley’s Comet
Second, comets are unlikely to deliver much water to Earth.
That’s because by studying the water ice of Comets Halley and Hyakutake, the only comets whose water molecules can be studied in detail, it was found that the comet’s ice is rich in deuterium atoms, a heavy isotope of hydrogen atoms.
If the earth’s water resources mainly come from comets, then the deuterium-to-hydrogen ratio (D/H ratio) of the earth’s water molecules will be very high now, but the actual situation of the earth is not high now.
In fact, the deuterium-to-hydrogen ratio of water resources itself will keep increasing during the formation of the earth. This is because deuterium is heavier than hydrogen. After the water molecules are photolyzed, ordinary hydrogen is more easily lost, which is why Venus This is one of the main reasons for the abnormally high deuterium-to-hydrogen ratio.
However, there is currently no known process on earth that can reduce the deuterium-to-hydrogen ratio. Even if an asteroid delivers water resources, the deuterium-to-hydrogen ratio of its water resources is basically the same as that of the earth’s oceans.
Early Solar System, Image Credit: NASA/JPL-Caltech
Therefore, the water resources delivered by comets can only be secondary, and the existing water resources on the earth are mainly from the formation of primitive planets. The possibility is the highest.
Of course, Earth probably didn’t get its own water molecules initially, but more hydrogen — the most ubiquitous element in the universe and the predominant element in any early nebula.
Afterwards, hydrogen combined with various other elements to form what we have today as water, as well as all other hydrogen-containing compounds.
However, it must be mentioned here that the earth’s water resources are often “polluted” in the subsequent crustal movement, and the amount of water resources on the earth’s surface is much lower than that in the earth’s interior. Studies have shown that the total water resources in the mantle are 3 times the ocean.
Figure: Earth Structure
Therefore, it is hoped that understanding the water resources of Mars can further understand the source of the planet’s water resources, because many researchers believe that Mars is rarely affected by plate tectonics.
How did Earth’s oceans form?
When we understand the source of the earth’s water resources, in fact, the formation of the ocean will come naturally. It is clear at a glance that as long as the earth cools enough to support liquid water, the ocean will naturally form.
Current research and observational data suggest that protoplanet formation grew out of constant accretion and collisions, but both processes release enormous amounts of heat.
Early Earth, Credit: SwRI/Simone Marchi
So the early Earth was so hot that everything was molten, so there was no question of whether liquid water existed.
As the planet stabilizes and no asteroids continue to crash into it, it will gradually cool down or cool down. The Earth is just in the habitable zone of the solar system, and the solar radiation it receives can support the existence of liquid water.
When the Earth itself cooled down, liquid water naturally appeared, but it took at least millions of years for Earth’s oceans to form — this is what’s known as the Earth’s millions of years of rain creating the oceans.
When the earth was hot, water was mainly present in the earth’s atmosphere in the form of water vapor, and after the earth cooled, it began to rain. This important turning point for the earth occurred about 3.8 billion years ago.
However, the rain is evaporated again at the moment or before it hits the ground, and the earth continues to cool down in the process of turning water into water vapor until liquid water can exist on the surface of the earth.
It is this process that has been going on for millions of years. At that time, the earth had strong convective weather all the time, which was very bad, but the interesting thing is that the lightning caused by strong convection may help later life form in the ocean.
Millions of years of rain have scoured the earth’s surface indiscriminately, eventually creating rivers and pools of water in original basins to form oceans.
The advent of the ocean has revolutionized the planet, including its modification of the composition of the Earth’s atmosphere—mainly the absorption of carbon dioxide by seawater, and the emergence of life.
at last
You may also be curious about the planets in the habitable zone of the solar system, including Venus and Mars, why only the earth eventually formed an ocean, and it can only be said that everything on the earth is just right.
The size of the earth is just right, and Mars is too small, and Mars does not have enough ability to maintain the core temperature for a long time; the distance between the earth and the sun is just right, and Venus is too close. After Venus was formed, the ultra-high carbon dioxide ratio in its atmosphere created Due to the global greenhouse effect, water can never exist in liquid form under sunlight.
But then again, it is a general consensus that the ocean is the cradle of life on earth, but if the water resources of the earth’s oceans are basically collected from the formation of the planet, then will life on earth be unique?
Hashtag: rain on earth’s oceans
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