Updated: Mar 31
By: Shaina Grover
We have all heard of the Big Bang. The incredible and, in some ways, unimaginable, beginning of the universe. But, do you know how the Earth turned from tiny particles in the air to an entire planet revolving around the Sun? Well, before we get into this, there’s something we need to understand: the formation of the planets was not instantaneous. It actually took hundreds and thousands of years. And even after that, life on Earth was still a far way out.
So, the Big Bang occurred 13.7 billion years ago; however, the Earth was formed only 4.54 billion years ago. That means the Earth didn’t form until approximately 9 billion years after the Big Bang!
The formation of the Earth can be explained by the Nebular Theory, which states that the Sun and planets were formed from a cloud of gas and dust—otherwise known as a nebula. What this essentially means is that our entire solar system started out as a giant cloud of gas and dust. At one point, this cloud collapsed into itself due to its gravity, and, as a result, several different clouds of gas and dust began to condense. The gravitational pull of these joined particles brought more and more particles towards it, increasing their size. Each cloud was composed of dozens of different layers of gas and particles. These clouds would go on to become planets.
The reason that these joined particles could grow to such massive sizes is that mass and gravitational force are directly proportional; larger mass means a greater gravitational pull. And so, as these conglomerates of gas and dust began to grow, they also started to rotate and contract due to the conservation of momentum, eventually all coming together to form a massive disk. This disk is formally known as the Protoplanetary Disk. At the center of this disk was the largest cloud of gas and dust, which would heat up, causing fusion to begin. After some time, the solar wind created by the fusion blew away the excess gas and dust, resulting in the creation of the inner planets. Soon after, the outer gas planets were formed by the remaining dust and gas that had been blown away. Interestingly enough, much of the leftover debris formed their own astronomical landmarks, such as the Asteroid Belt, the Kuiper Belt, and the Oort Cloud.
During this entire process, the constant collision of particles and the rotation of the disks led to huge increases in the area’s temperature. The reason that the collision of these particles resulted in an increase in temperature can be explained by the Kinetic Molecular Theory. The Kinetic Molecular Theory states that all matter is composed of tiny particles that are in constant motion. The kinetic energy of these particles, combined with their potential energy, results in thermal energy. Thermal energy, of course, means heat. And so, with every collision of gas and dust particles, the more heat there was. As a result, by the time the Earth was its current size, its temperature was so high that it was a mass of hot, molten rock.
Over time, the rate of collision slowed, leading to the Earth’s surface cooling down and the solidification of its crust. However, its interior was still molten. Furthermore, it was also made of several different substances, many of which were liquids. And, as you may already know, liquids with different compositions don’t usually mix together. For instance, if you attempt to mix oil and water together, you’ll find your attempts unsuccessful. Instead of a mixture, you’ll end up with two layers of liquids: oil at the top and water at the bottom. This is because water is denser than oil. Density is the measure of compactness of an object. Even though different masses of a given material may have different volumes, their density is the same because the way the molecules are organized does not change with mass or volume.
And so, similar to the way oil and water don’t mix, the different liquids inside of the Earth settled according to their densities in a process called differentiation. The densest substances settled at the bottom/center of the Earth, whereas the less dense substances rose to the top. As a result, the Earth’s core is in the very center of its being, and is followed by the mantle, crust, and then the atmosphere. The densest substances settled in the middle due to the fact that their molecules were very close together and compact.
Now, even though the Earth was technically “formed” at this point, it did not look like anything like the Earth we live on today. It took a very long time, as well as various changes to the Earth, both internal and external, to get to the point we are today.
In conclusion, the Earth’s surface has evolved greatly throughout its lifespan of 4.5 billion years, as have the other planets. Yet one thing remains the same: Even today, the Earth and the other planets in our solar system continue to orbit the Sun as they have been doing since they started forming. However, we can only imagine how they will continue to change in the future.
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What Did You Learn?
1. What are the different types of kinetic energy and what do they all mean?
The three types of kinetic energy are translational, rotational, and vibrational kinetic energy. Matter has translational kinetic energy when it moves in a straight line. When it rotates, it has rotational kinetic energy, and when it vibrates, it has vibrational kinetic energy. Particles also have potential energy due to the attraction or mutual repulsion between particles when they are close together.
2. How do we know when Earth formed?
One thing scientists use to determine the age of the Earth is a process called carbon dating. Every living organism absorbs a certain quantity of Carbon-14, and when this living organism dies, it stops absorbing Carbon-14, but continues to lose it. When the dead organism is found, scientists can identify how much the Carbon-14 has decayed and use the half-life of the Carbon to identify how long it has been dead for. Furthermore, by finding the oldest rock on the Earth’s surface, and identifying how old it is, scientists can figure out how old the Earth is. At the moment, the oldest rock/crystal we know of is the Zircon Crystal, which is approximately 4.3 billion years old.