While there are many scientists who believe in a Creator perfectly forming our world, those who won’t believe that seek other explanations. This describes their conclusions.
Many cosmologists believe that the universe originated from a single location that consisted of all the matter and energy of space. They believe that about 15 billion years ago an explosive event expanded the matter and energy to form our universe. They call this rapid expansion “the Big Bang.” They believe hydrogen and helium gases formed as a result of the Big Bang and that the Sun and the planets originated from a cloud of dust and gas called the nebula. They say this cloud of gas and dust began to swirl, rotate, and expand into a flatten disk shape structure. Watch the disk formation below.
Here’s further description of what these scientists believe.
The inner planets were formed near the center of the rotating flattened disk. These planets are called the terrestrial planets. They are rocky and denser than the outer planets. They consist of rocks made from silicate minerals and the metal iron. Mercury, Venus, Earth, and Mars are the terrestrial planets.
The outer planets are called the gas giants. They are less dense than the terrestrial planets because they consist of mostly gases and ice. The ice is made up of methane, carbon dioxide, ammonia, and water. These larger planets are also known as the Jovian planets. Jupiter, Saturn, Uranus, and Neptune are the four Jovian planets. Pluto is no longer considered a planet. In 2006, the International Astronomical Union (IAU) classified Pluto as a dwarf planet based on their new scientific definition of the word “planet.”
Scientists believe that the inner planets are smaller than the outer planets because of heat. The higher temperatures near the center of the nebula may have led to the lack of the formation of ice on the inner planets. The outer planets form further away from the center of the nebula. It was cold enough to allow ice, gases, solid metals, and minerals to accumulate into a greater size compared to the terrestrial planets.
The mass, temperature, and gravity of the planets affects their atmospheres. The Jovian planets have a thick atmosphere made up of mostly hydrogen and helium. Their large size contributes to the strong amount of gravitational force between a planet and its atmosphere. The gases that make up their atmosphere were not able to escape. The terrestrial planets may have a thin atmosphere or no atmosphere at all. Their surface gravity is not strong enough to retain a lot of gases in their atmosphere.
Although Earth and Venus are referred to as the “sister” or “twin” planets, they have very different atmospheres. Venus’ atmospheric pressure is about 92 atm. The atmospheric pressure on Earth is 1 atm. Venus also has sulfur dioxide and a higher concentration of carbon dioxide in its atmosphere. The surface on Venus is extremely hot. It is about 464°C. That is hot enough to melt lead. The two planets are very similar because they have almost the same size, density, and mass.
The Sun formed at the center of this structure. Gravity caused clumps of matter to collide and join together during a process called accretion. This process led to the formation of planetesimals which would eventually form the stars and planets of our solar system. This explanation for the formation of the solar system is known as the nebular hypothesis.
They also believe the Earth’s atmosphere changed over time, that organisms used the carbon dioxide in the environment to produce oxygen, increasing its amount in our atmosphere.
(edited from source)