Eon: Proterozoic
(/prōdərəˈzōik/)
2.5 BYA - 541 MYA
Eras:
During this Eon, free oxygen began building in the atmosphere, and shallow inland seas provided excellent warm water incubators for the earliest complex lifeforms to grow. Multicellular life began at this time, as did sexual reproduction.
The Proterozoic experienced both hot and cool climates, that at one more than one point in it's history resulted in a major glaciation that may have encompassed much of the globe.
The Earth was undergoing several tectonic shifts at this time, similar to today's moving continents with the leading continent of the age being the Rodinia Supercontinent.
Updated 3/2020
Earth Eons
Description Biology Geology Short
Characteristics: The first easily identifiable fossilized lifeforms. Inland seas. Early mountain ranges. Primitive multicellular life forms and sexual reproduction all appear at this time. Free oxygen begins to accumulate in the atmosphere.
Description -
The bacterial mats of the Archean, now formed more complex organisms (eukaryotes, cells with a membrane wall surrounding a nucleus). They spent more than 500 million ancestral years evolving from single celled organic matter in the competitive waters of this early earth to reach this stage. This development roughly coincided with another major event in Earth's history, the introduction of free oxygen into the atmosphere. Oxygen was being produced at an ever increasing rate by cyanobacteria. Prior to this, more primitive bacteria thrived on the atmospheres sulfur production. All living plants today still have a symbiotic relationship with some form of cyanobacteria, even all these billions of years later (SA).
Much of the Proterozoic consisted of inland seas, which served as excellent breeding grounds for life. Early oceans continued to be supplied hydrogen and oxygen by meteorites that had these two elements trapped within them. Today, Earth itself is believed to hold enough "trapped" hydrogen in it's rocky mantle to support 10 oceans (Ast).
Super-continents had also begun forming (also known as "continental accretion") a process that started at the end of the Archean. These land masses gave rise to the first mountain ranges. Glaciers may have also formed at this time (there is evidence in the sedimentary deposits of this time) and possibly occurred over four separate periods. The most noted example of this is the hypothesized "Snowball Earth" when the vast majority of the planet may have become nothing more than a slushy ice ball, or frozen tundra. This occurred before the great radiation of life in the Cambrian, also known as the Cambrian explosion.
Biology -
Multicellular life begins, as does sexual reproduction. There are no great examples of animal life until the following Eon, and it's famous Era the Cambrian (541 MYA - 485.4 MYA).
Geology -
During the Proterozoic, the largest most notable continent was Rodinia. This supercontinent would continue to undergo continental shifting until it's ultimate breakup 750 - 633 million years ago.
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