6  Milky Way galaxy was already well-formed and had undergone several mergers with smaller galaxies. |
| 6  Many stars, including ancient Population II stars, were shining in the galaxy. |
| 6 heavier elements (carbon, oxygen, iron) necessary for forming rocky planets were slowly building up from supernovae. |
| 6Â active star formation, particularly in spiral galaxies like the Milky Way. |
| 6  Many of the Sun-like stars that exist today likely formed around this time. |
| 6  Cosmologists estimate that dark energy began to dominate the universe's expansion around this time (~5–6 billion years ago), accelerating the rate at which galaxies move apart from each other. |
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| 5 Sun began to form in a region of a molecular cloud, also known as a nebula, made up of gas and dust. This process is called stellar formation. The collapse of this cloud under gravity triggered the birth of the Sun, which then ignited nuclear fusion in its core, becoming a star. |
| 5 material in the surrounding disk began to coalesce, forming the planets, moons, and other objects in our solar system. This period marks the beginning of what we now recognize as the solar system, and it's considered the starting point of the "solar nebula" theory of planetary formation. |
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Precambrian Eon
4.6 - 541 4.059
4.6  Earth formed |
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Precambrian Eon
4.6 - 541 4.059
Hadean Eon
4.6 - 4 .2
Pre-Nectarian Period
4.533 - 3.92 6.136
| 4.1 Earliest biotic life reproducing RNA molecules require energy, space & smaller blocks, which become limited so Natural selection favors molecules good at replication. DNA develop inside stable physical & chemical membrane for proto-cells |
4 - 3.8  Earliest Life. single-celled microorganisms (possibly bacteria or archaea), are believed to have begun evolving in the oceans. |
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Nectarian Luna Period
3.92 - 3.85 .07
3.9  cataclysmic cratering
>22,000 craters diameters >12/20 40 diameters 620/1,000
several diameters 3100/5000 |
3.9 - 2.5 1.4  meteor cluster |
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Precambrian Eon
4.6 - 541 4.059
Archean Eon
4 - 2.5 1.5
| Mesoarchaean Era 3.2 - 2.8 400M |
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cool early Earth theory  modest influx of 
Solar System formation
Earth 
4.5 billion-year-old meteorites found on Earth that contained liquid water alongside a wide diversity of deuterium-poor organic compounds 
water & atmosphere
Late Heavy Bombardment lunar cataclysm 
Oxygen
Photosynthesis