The Precambrian , aka "Deep Time" frame makes up roughly 90% of geologic time. This is when Planet Earth formed, simple life began, oxygen enriched the atomosphere, tectonic plates formed and shifted, and eukaryotic cells evolved. This vast amount of time in the earth's history is broken down into three periods, Hadean, Archaean, and Proterozoic.
Hadean is the period from 4.5 to 3.8 billion years ago in which the earth formed, but it started as a molten blob. This is when the solar system was forming and the sun began to produce light and heat by way of nuclear fusion. Particles lumped together that eventually formed the planets that we see today. Molten iron fell to the middle to form the core and lighter elements arose to form the crust. Earths early atmosphere was also established during this time by outgassings of volatile molecules such as water, methane, hydrogen, nitrogen, ammonia, and carbon dioxide. Over the first 800 million years, or so, temperatures started to cool down and thus resulted in the formation of
rocks, which leads into the Archaean period.
Archaean 3800 to 2500 mya
The Archaean period is when the oldest rocks formed from cooling of molten material. The Isua Supracrustal rocks found in West Greenland are belived to be between 3.7 -3.8 billion years old and rocks from the Acasta Gneiss Complex in Canada are estimated to be around 4.03 billion years old. Rocks that exceed 3.5 billion years old have been found on every one of the continents.
During the Achaean period is when the first life on earth formed even with a atmosphere of methane, ammonia, and other gases that would be toxic to most life on our planet today. The oldest fossils are of bacteria and are dated to be around 3.5 billion years old and are of Cyanobacteria or blue-green algae. These bacteria belong to the group of prokaryotic cells, which lack mitochondria, chloroplasts and a nucleus. These cyanobacteria grouped and formed massive mats of stromatolites during the late Achaean period and into the Proterozoic period.
Proterozoic 2500 to 544 mya
Many of the most important events in the history of the earth and life occurred during Proterozoic era, which means "early life". Stromatolites increased during this time and produced oxygen that supports our life system now. During this time continents first appeared and became stable and began to slowly grow.
During the Proterozoic era is when life changed on earth, around 1.8 billion years ago eukaryotic cells first appeared. Eukaryotic cells are organisms that contain a distinct nucleus and other complex internal parts; all plants, animals, fungi, and protists are eukaryotic.
From around 650 to 544 m.y.a, known as he Vendian period, the first animals appeared. These animals were worm like soft-bodied organisms that have been found around the world.
