Approximately 4.6 billion years ago our solar system started to form. The Big Bang being 9.2 Billion years before our own solar system started to form. By this time the universe looked pretty much as it does now due to the 9.2 billion years worth of expansion and cooling.
Within those 9.2 billion years hundreds of billions of stars had formed, lived and died to generate massive nebula clouds of gas and dust to form solar systems all over the galaxy. Heavier elements also had the chance to form naturally throughout the cosmos aswell. By this time plenty of stars had generated most of the natural elements necessary to make planets and more stars for them to orbit.
The accepted scientific age of the Earth is 4.54 billion years old. How do we know this? Radiometric dating. Radiometric dating is used to calculate the half lives of natural elements. Rocks on Earth contain certain minerals and elements. Meteorites were used to calculate the age of the Earth as the core/mantle of our planet has changed frequently throughout it’s 4.54 billion years of existence.
Uranium over billions of years decays to lead. The oldest samples of meteorites are 4.6 billion years old and so far nothing has been verified as older. This leaves us to accept the age of the solar system as 4.6 billion years old or so.
The rocky early solar system collapsed over 10-20 million years to form the Earth. The solar system was extremely hectic at this time. Loose matter began to accumulate and collapse under the influence of gravity to form stars and our planets. Interestingly, the theory for the moon’s formation was that a large object now named Theia impacted the Earth at a glancing blow. The matter flung from Earth on impact collapsed to form the moon.
The next phase was hell! We call it The Late Heavy Bombardment (LHB) or the Lunar Cataclysm. During this time a large number of asteroids impacted the inner early planets; Mercury, Venus, Earth, Mars and also the Moon. This accelerated the mass of the planets very early on in their histories. All of this took place between 4.1 and 3.8 billion years ago.
Volcanic activity on the Earth was widespread at this time. Ejecting greenhouse gases into the heavens which contributed to the formation of our atmosphere we have now. The protective layer of the Earth. A sizeable quantity of water may have been within the insterstellar material the Earth was formed from. Another valid theory is that the Earth may have been struck by water rich meteors and comets in its infancy. Water can form and exist in the universe in large quantities. Water didn’t form and it doesn’t exist only on Earth!
Oceans would have existed and formed slightly later and would still have been liquid water even when the Earth’s temperature was 230 degrees. I know that is above boiling point but the high concentration of carbon dioxide in the early atmosphere kept it in liquid form. The oceans then did its work in depleting the carbon dioxide in the atmosphere.
The cooling of volcanic material left us with land and a whole biosphere that life could flourish in. Living matter then began to develop from non-living matter, what we call abiogenesis. Life formed around a billion years after the Earth started to form. Hydrothermal vents under the sea are the most likely places living matter began to develop. Single celled organisms, prokaryotes, carry a DNA structure and further evolved into the living matter and energy that is abundant all around us now.
Using radiometric dating on the earliest Earth Rock samples, evidence of these single cells are fossilised within, so determining the formation of Life on Earth is reasonably straightforward. Cells evolving to allow photosynthesis give our atmosphere the oxygen content it has today and allowed life to further evolve and develop.