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How Was the Planet Earth Formed?

We all know that planets revolve around the stars in the Galaxy. But their formation continues to remain a big question. One such question was – How was the planet Earth formed? With time we collected data on this and therefore today we partially understand how planet Earth formed.


How many years ago was the Earth formed?

There exists a planetarium of the Akash Ganga. We have presently known it as the Milky Way. The formation of our Earth happened about 4.5 bn years ago, i.e., 450 crore years back. Isn’t it fascinating? But life appeared almost 0.5 bn years after the formation of the Earth. Back then, Earth was all set to start its journey.

How Was the Planet Earth formed?

You all might have heard about the Big Bang theory which attempts to explain to us the formation of the universe. It talks of a huge explosion from which all the planets and heavenly bodies emerged. At present, two theories are widely accepted by many scientists that account for the formation of our mother planet Earth:

  • Core Accretion Theory
  • Disk instability Theory

Core accretion works well with the formation of terrestrial planets like Earth but has some problems in explaining the formation of giant planets.

On the other hand, disk instability theory, best explains the creation of these giant planets. Let’s understand the theories better:

The Core Accretion Model

The beautiful solar system that we all see in our social studies and science books; was just a cloud of dust and gas about 4.6 billion years ago. It was the solar nebula. As it began to spin, gravity collapsed in on itself resulting in the formation of a bright star, the Sun.

As the sun started rising, tiny particles, influenced by the force of gravity, began piling up. Over a certain course of time, they transformed into larger particles. Under the pressure of solar wind lighter elements such as hydrogen and helium moved away.

The result was that it left heavy and Rocky materials behind which became the foundation for both smaller and giant terrestrial planets. As time went on, the effect of solar wind decreased on lighter elements, forcing them to converge into gas giants. These later formed the atmosphere for many planets. In this way, present-day planets, comets, meteors, asteroids, came into existence.

What Happened Next?

Earth’s outer solid core formed first, with denser and heavy materials colliding and sticking together. The denser materials formed the inner and outer core. And, the lighter materials rose to the upper part and formed the mantle and crust. Earth’s magnetic field probably came into existence by this time.

There was no atmosphere on the early earth. Water vapour, carbon dioxide, methane and ammonia released from molten mass covered the Earth’s surface. The ultraviolet rays split water molecules into oxygen and hydrogen from which the lighter H2 escaped.

The combination of oxygen with ammonia and methane to form water and CO2 resulted in the formation of the atmosphere. The ozone layer also came into existence by the time. As the temperature dropped, water vapour fell as rain. Rain filled all craters which later formed oceans. Since the planet is in the Goldilocks zone, it contains water that neither evaporates nor freezes. The scientists had enough proof to consider this as an important factor in the origin of life.

Wow! That Is Mind-Blowing. What Do Scientists Think About This?

Exoplanet observations confirm the core accretion model. Therefore, scientists believe it as a dominant formation process. According to NASA, stars with more “metals” contain denser planets in their cores as compared to other metal-poor cousins.

An example of an exoplanet that helped scientists know this model better is the discovery of a giant massive planet. It was found orbiting a sun-like star HD 149026 in 2005.

Greg Henry is an astronomer and research scientist at TSU (Tennessee State University), Nashville. He said in a press release, “All these observations prove the core accretion thesis for the formation of terrestrial planets”.

The Disk Instability Model

Even though the Core Accretion theory worked fine for smaller terrestrial planets, there were some issues. It couldn’t properly explain the formation of gas giants. The reason being that they evolve rapidly to grab hold of the mass of lighter gases.  Also, the Core Accretion theory faces another problem as the baby planets start spiraling into the sun within a short duration of time.

The new Disk Instability model explains how the clumps of dust and gas aggregate together to form giant planets early in the life of the solar system. These planets can form faster as compared to their core accretion rivals. Within a span of thousand years, it allows them to trap lighter gases rapidly. They also acquire sufficient mass that helps them keep revolving around the sun thus reducing their possibility of death-marching into the sun.

What Do the Scientists Say?

Paul Wilson, an exoplanetary astronomer explains that the second theory of formation of planets. This theory results in the production of a large number of worlds at large orders. Out of the four giant planets orbiting around the star HD 9799; Fomalhaut b (an exoplanet), provides observational evidence for disk instability.

A New Theory: Pebble Accretion

Time is the biggest challenge to core accretion. How do massive gas giants build themselves fast enough to grab lighter components of the atmosphere? There is recent research that builds a new theory on how was the planet earth formed. It is called Pebble accretion Model.

Michiel Lambrechts and Anders Johansen who are researchers from Lund University in Sweden had something new to share.  They showed how small and tiny pebbles that were earlier uprooted played a key role in the creation of rapidly evolving massive planets.

Levison along with his team researched the previous proposition more accurately. They came to a concrete conclusion that tiny pebbles had aggregated together; to form the planets we see in the present Galaxy.

According to Levison’s simulations, large particles act like bullies that snatch away the small-sized pebbles to grow and at a very faster rate. “The bigger guy consumes the smaller ones themselves and continues to grow up to form the cores of the giant planets,” says Katherine Kretke, also from SwRI.


The solar system is continuously growing. The question doesn’t end with how the planet Earth was formed. Our solar system is forming new things as well as destroying some others. Scientists continue their journey to understand and discover our solar system as well as other systems. The more they research the better they will come to know how our mother planet earth and its siblings formed.

Did you find these facts interesting? If yes, you can also watch a video that explains how was the planet Earth formed.

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