Hadean, Archean, and Proterozoic By: Gabe M, Emily C, Zack R, & Akasia E.
TIME PERIOD: 4.6- 4 billion years ago
GEOLOGY: The Earth was in a constant state of extreme heat. At first it was a ball of molten material. Planetoids and meteorites constantly pummeled the Earth and brought water. This water evaporated, creating a steam atmosphere. Later, at about 4.3 billion years ago the Earth began to cool and this steam fell as rain. This precipitation caused the oceans to form. At about 4 billion years ago continents started to form, causing the Earth to move to the next stage, the Archean Era.
ORGANISMS: No organisms were able to survive during this era. The constant melting of the Earth's surface and meteorite impacts caused heat that would kill most living things.
ROCK TYPES: The Earth was too hot to form any rocks. It was constantly melting.
THE ARCHEAN ERA
TIME PERIOD: 4 billion-2.5 billion years ago
GEOLOGY: The Earth was covered in oceans, even though it was three times as hot. The Earth was cool enough to form continents. Before this, lava would never cool so land couldn't form. Most scientists believe that by the end of the Archean era there were small continents (like in the map below), but others believe that the continents were close to the size of continents today. These were created by volcanic and tectonic activity. The atmosphere was mostly made up of Nitrogen and Carbon Dioxide
ORGANISMS: In this era there was evidence of bacteria and blue-green algae. Most organisms were single-celled and prokaryotic. About 3 billion years ago the first photo-synthesizers popped up. They began creating large amounts of oxygen, but this oxygen stayed in the rocks, which is backed up by evidence of rust in the rocks during this time period. Rust can only be created with the presence of oxygen.
ROCK TYPES: The three rock types most characteristic of the Archean era are granite, gneiss, and greenstone. There were also a vast array of igneous rock (basaltic, andesitic, and rhyolitic).
THE PROTEROZOIC ERA
TIME PERIOD: 2.4 billion to 541 million years ago.
DESCRIPTION: Proterozoic represents the time just before the proliferation of complex life on earth. It is the younger division in two from the Precambrian time. The dates at which the Proterozoic Eon extends from 2.4 billion to 541 million years ago. It is divided by the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic. During this Eon, the oceans and atmosphere changed significantly.
GEOLOGY: During this era the continents continued to grow. At one point they joined to form the super-continent Rodinia. Another large event was an ice age around 600 million years ago. The Earth had cooled significantly since the last era, the Archean era.
ORGANISMS: The rocks in this period contain fossil remains of bacteria and the blue-green algae. This also includes the first oxygen dependent animals Ediacaran Fauna. 2.3 billion and 1.8 billion years ago oxygen began to spread throughout the atmosphere. Photo-synthesizers played a major role in the production of oxygen during this Eon.
ROCK TYPE: There were 2 different types of rock during this time period. Those being basilica, rhyolitic.