What are the three theories on how Earth was formed?

As of my last update in September 2021, the three prevailing theories on how Earth was formed are:

Nebular Hypothesis: The Nebular Hypothesis is one of the most widely accepted theories on the formation of the solar system, including Earth. According to this hypothesis, about 4.6 billion years ago, our solar system began as a massive cloud of gas and dust called a solar nebula. The nebula started to collapse under its gravity, and as it contracted, it began to spin faster. Most of the material accumulated at the center to form the young Sun, while the remaining gas and dust gathered in a flattened disk around it. Over time, this disk of material accreted to form the planets, including Earth.

Planetesimal Hypothesis: The Planetesimal Hypothesis is an extension of the Nebular Hypothesis. According to this theory, as the dust and gas in the solar nebula began to clump together, small solid bodies called planetesimals formed. These planetesimals were the building blocks of the planets. Through further gravitational attraction and collisions, these planetesimals merged to form larger and larger bodies, ultimately leading to the formation of Earth and other planets.

Giant Impact Hypothesis (Theia Impact): The Giant Impact Hypothesis proposes that a celestial body, often referred to as "Theia," collided with the young Earth approximately 4.5 billion years ago. The impact was so massive that it ejected a significant amount of debris into space. This debris eventually coalesced and formed the Moon. This theory explains some characteristics of the Moon and its relatively low density compared to Earth. It is important to note that this hypothesis is specific to the Moon's formation rather than the Earth itself, but it is often considered when discussing the early formation of Earth-Moon system.

These theories are supported by various pieces of evidence, such as planetary compositions, computer simulations, and observations of other star systems, but they are still subject to refinement as scientific research progresses.