Earth, as you all know is the only planet in the universe where we are aware of the existence of life. The main thing which makes the earth different as well good for living is the content of water and atmosphere. It is about three-quarters of the earth's crust is water. It is a great coincidence that all the conditions like gravity, atmosphere and distance from the sun all come in such a way that life can survive. Though we are in a great endeavour to find another earth-like planet in the observable universe where there is a trace of life, we couldn’t able to get any. Here these article points out the formation of the earth and its structure.
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The formation of the earth and other planets
It is believed that the earth was formed about 4.54 billion years ago from the solar nebulae (by the accretion of the solar nebula), the same way as the other planets, asteroids and the majority of the moons in the solar system formed. This model is known as the Nebular hypothesis, developed in the eighteenth century by Immanuel Cant, Immanuel Swedenborg and Pierre-Simon Lapse.
What the heck is a Solar nebula?
Before getting to this, first, learn how really stars form. The sun and usually all the stars are formed by the gradual gravitational collapse of a cloud which contains dust, gases in ionic, atomic and molecular form, cosmic rays, etc. (commonly known by the name interstellar matter).
Similarly, the formation of the sun occurred because of the gravitational collapse of a large molecular cloud (about 20 parsec or 65 lightyears across) from which most of the collapsing mass collected in the centre and formed the sun and the small amount that remained flattened into a protoplanetary disk. This disc is what we call the name solar nebula.
In simple words, Solar nebula is the disc-shaped mass of dust particles, gases and other particles left over by the formation of the sun.
These disc-shaped masses which were rotating around the sun, over the course of time, collided with each other and clumped together to form the planets of our solar system (asteroids, most of the moons (except some of the moons of certain planets like that of the earth (this will be discussed below)) and other solar bodies were also formed the same way).
Early earth
The early stage of planets was molten and so hot that we can’t imagine. The hotness was because of the transformation of the energy from those violent collisions that happened in between the countless small bodies of the disc-shaped masses which clumped together to form the planets.
The early earth was also like the other planets, a hot molten celestial body. Eventually, the hotness decreased and the surface became solid. But until now, the hotness is not completely cooled. The core and a certain portion of the mantle of our earth are still hot and molten. It is estimated that the temperature in the core is about 3800 degrees celsius to 6000 degrees celsius.
This high-temperature hot molten material inside the earth is what we see as lava coming out from the volcanoes.
Why does the inner earth remain hot?
There are mainly three reasons for this:
- The hotness of the early molten earth hasn’t been cooled completely yet
- Because of gravity which is pulling matter towards the centre. This compression exerted on the internal materials increases the heat.
- Since the formation of the earth, it has been emitting heat outside of space. Due to this, certain radioactive elements inside the earth such as Potassium, Titanium, Thorium, etc, undergo radioactive decay (the process of breaking down). This as well releases energy. So the radioactive decay in the mantle and earth's crust prohibits the cooling of the Earth.
The twist in the story!
When I wrote about the formation of moons(natural satellites), I said that the moon that our earth has wasn’t formed the same way as most of the others did.
There exists a hypothesis that once in the history of time (about 4.5 billion years ago), a giant body hit our early earth. The giant impact done by that planet-sized body(similar to the size of Mars) named Theia caused the formation of the moon.
The parts blasted out from the earth and most of the part of Theia formed a disk surrounding the earth like that of the disk we see around Saturn. This gradually clumped together over time to form the Moon!
We can call this theory the Giant-impact hypothesis.
Read more about the Formation of moon: Click here
How water had formed on the earth.
Everybody obviously knows that three-quarters of our earth's crust is filled with water. But the perplexing question is who filled it?
Water is the main thing which makes our planet different from those of the other planets in the solar system. It is because of the presence of water that life originated on earth. Unless earth would have remained the same as the other planets.
A doubt may arise in everybody's mind that why earth is the only watery planet in the solar system? For answering this, we should have to know how water had formed on earth.
This is a matter which caused a lot of controversies in recent times. There are a lot of opinions among different scientists. Here we will learn about the few with strong bases.
Most scientists believe that water formed not on earth but was brought to earth by the asteroids which fell on the dry young earth. This hypothesis was of great popularity till recent times. And yeah, a lot many still believe it.
Far away from the sun, in places with extremely low temperatures, water formed icy comets. When they reached closer to the sun, the water slowly reacted with the rocky wandering materials in the space to form hydrated ones. These new hydrated materials (asteroids) fell on the earth and due to the hot surface turned to vapour. But due to the gravitational force of earth, the vapour couldn’t get out to space. So it remained in the earth’s atmosphere and slowly condensed with time to pour copious down as the longest rain for years. This not only made the earth come cool but also helped in the formation of vast oceans.
Hey, are you saying that the entire oceans are formed by the water deposited by the asteroids?
Well, it may sound funny if you think from the perspective that asteroids fell fiercely as how now does.
In the young solar system, everything was in a violent state. Planets, asteroids, giant bodies and everything were in rapid motion. In those times, asteroids and comets were showering on planets like rain. This is what caused a large amount of water to transfer from space to earth.
Then why the water didn’t form on other planets the same way?
This is what we really want to say as the real blessing. Our earth lies in the Goldilocks zone (the zone classified according to the distance from the sun). In this zone, water can exist neither evaporating nor freezing but on caring about the other planets in our solar system, the temperature of planets before the earth (Venus and Mercury) are extremely high and water can’t lie in a liquid state. In the case of planets beyond earth, the condition is the opposite (so cold!).
Anyway, there are many other theories that made this hypothesis fade its popularity.
Here are some of the recent theories:
- Water formed along with the formation of the earth
- Formed from the hydrogen that was inside the earth.
- Formed when Theia collided with the earth (formation of the moon)
Formation of the atmosphere.
When Earth formed, it was a hot molten place with no atmosphere. When it gradually cooled, it got a solid crust. Dense materials sank into the centre while less dense materials went up to build the crust up. The atmosphere was formed from the gases spewed out from the volcanoes that then exist. These gases include carbon dioxide with the maximum amount (approximately about 97%), nitrogen (approximately 3%), ammonia, hydrogen, hydrogen sulfide, etc.
What about now?
Whenever I gaze up at the moon, I feel like I'm on a time machine. I am back to that precious pinpoint of time, standing on the foreboding - yet beautiful - Sea of Tranquility. I could see our shining blue planet Earth poised in the darkness of space.
-Buzz Aldrin
Now the earth is something like heaven than a planet. With all these times, many changes happened occurred on earth.
Here are some brief details of the structure of the modern earth:
Earth's atmosphere is comprised of majorly five layers:
- Troposphere
- Stratosphere
- Mesosphere
- Thermosphere
- Exosphere
The inner earth is also divided into four:
- Inner core
- Core
- Mantle
- Crust
Of all celestial bodies within reach or view, as far as we can see, out to the edge, the most wonderful and marvellous and mysterious is turning out to be our own planet earth. There is nothing to match it anywhere, not yet anyway.
-Lewis Thomas
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