Notes to Self on Geologic Time : Part 2 - Precambiran Seas and Early Earth

PRECAMBRIAN 4.5 bya - 550 mya

4.5 billion years ago - The earth was born

Around this time the earth was beginning to from the a dense cloud of rock and dust floating around the sun called an accretion disc.  Eventually this hot mass formed into a system consisting of the planets, planetoids and belts that we are all familiar with today. This era is also known as the Hadean era but I'm not going to go too much into this since this for now.
 
The Precambrian had two primary eras: the Archaean and Protozoic.

Archaean 3.8 to 2.5 billion years ago

• Earth really begins to solidify and continental plates begin to form. 
• Sun around 1/3 dimmer than today.
• Reducing atmosphere of Methane, ammonia and other gasses. Little bit toxic to us aerobes. 
• First fossils showing life called Stromatolites. These can still be seen today in Australia! This began the oxygenating of the atmosphere. 
• First prokaryotes - lacking nucleolus.

Proterozoic Era - 2.5 billion to 543 million years ago

• First Stable continents
• First Ice Ages
• Oxygen levels continued to rise thanks to the photosynthesis of the stromatolites. Around 2.3 bya iron and sulfur had oxidized to the point that significant O2 was able to accrue in the atmosphere. 
• First eukaryotes and multicellular life. 
• Cnidarians develop
• End of the Protozoic we see the beginning of animals and skeletal structures.