Proterozoic Eon
Animals
The Proterozoic Eon lasted from 2.5 BYA to 542 Million Years Ago. The term
"Proterozoic" comes from two Greek terms, "proteros"
meaning "first" and "zoon" meaning "life". This
means that this eon is the first eon with multicellular life. Along with all
the new life, came a changing atmosphere and change in earth's land masses.The first fundamental change happened with the appearance of eukaryotes. Eukaryotes were the first cell with organelles, which are the organs of cells. Many scientists think eukaryotes evolved from prokaryotes, which are cells without organelles. Some prokaryotes evolved into eukaryotes due to the change in the earths atmosphere. Many prokaryotes depended on chemosynthesis (the process of deriving energy from chemicals) instead of photosynthesis for their energy. With more oxygen, cells had to evolve in order to survive. Many species of the time went extinct due to the dramatic increase of oxygen over the Proterozoic eon, but eukaryotes flourished.
The first unicellular eukaryotes were acritarchs, which came about around 2.1 BYA. They were the most common fossil found among the late Proterozoic era. Some are thought to be the ancestors of modern day planktonic algae.
The first possible multicellular eukaryote was the Grypania Spiralis, which looked like coiled ribbon. It was two millimeters wide and over ten centimeters long. It is controversial whether or not the Grypania was eukaryotic, so the first eukaryote could have been the Horodyskia, which is dated at about 1.5 BYA.
The first known multicellular animal was the Ediacaran Fauna, it resembles a modern day jellyfish and segmented worms. The creatures of the Proterozoic eon, like the Ediacaran Fauna, didn't have skeletons and/or protective shells like the animals in the Cambrian Period.
The first unicellular eukaryotes were acritarchs, which came about around 2.1 BYA. They were the most common fossil found among the late Proterozoic era. Some are thought to be the ancestors of modern day planktonic algae.
The first possible multicellular eukaryote was the Grypania Spiralis, which looked like coiled ribbon. It was two millimeters wide and over ten centimeters long. It is controversial whether or not the Grypania was eukaryotic, so the first eukaryote could have been the Horodyskia, which is dated at about 1.5 BYA.
The first known multicellular animal was the Ediacaran Fauna, it resembles a modern day jellyfish and segmented worms. The creatures of the Proterozoic eon, like the Ediacaran Fauna, didn't have skeletons and/or protective shells like the animals in the Cambrian Period.
Atmosphere
Before the Proterozoic Eon, there was little oxygen in earth's atmosphere, but during this eon, oxygen increased in the atmosphere due to the development of photosynthetic organisms. Photosynthetic organisms create oxygen from sunlight. An example of a photosynthetic organism is the cyanobacteria which dates back to about 2.7 BYA, but significant amounts of oxygen didn't exist until about 2.3 BYA. It took a while for free radicals of oxygen to be released into the atmosphere because the first free radicals of oxygen were used by the oxidation process of surface rocks and iron that dissolved into the ocean during the Archean Eon. The iron then turned into magnetite (Fe3O4) and sunk to the bottom of the ocean. Finally, after the weathering and oxidation processes, free oxygen was finally released into the atmosphere.
When iron is exposed to oxygen it rusts, which changes its color to reddish brown. This red color is characteristic of red beds that are made of the chemical reaction between oxygen and iron, which created hematite (Fe2O3). Hematite was created from the oxidation of iron that was on the land. Most banded iron formations were precipitated between 2.5 and 2 billion years ago. Red beds appeared directly afterward, 2 to 1.8 billion years ago, only after there was free oxygen in the atmosphere and red beds continue to develop today.
When iron is exposed to oxygen it rusts, which changes its color to reddish brown. This red color is characteristic of red beds that are made of the chemical reaction between oxygen and iron, which created hematite (Fe2O3). Hematite was created from the oxidation of iron that was on the land. Most banded iron formations were precipitated between 2.5 and 2 billion years ago. Red beds appeared directly afterward, 2 to 1.8 billion years ago, only after there was free oxygen in the atmosphere and red beds continue to develop today.
Land Masses
During the Proterozoic Eon, while the oxygen was rusting iron on the surface, mountains were beginning to build. Mountains build due to two or more plate tectonics merging together. When these plates converged, molten granite melted the igneous rock around the outer edges of what used to be micro-continents. The mountain building during the Proterozoic era expanded Northern America.
Many land masses at this point were conjoined into one large supercontinent, called Rodinia. By the end of the Proterozoic Eon, these land masses were starting to detach from each other due to a severe glaciation.
Many geologists believe the Proterozoic Earth was covered in glaciers for several million years. Others believe the glaciations happened at least twice during the Proterozoic, once in the beginning and once in the end. Until the Earth warmed up due to carbon dioxide being released from volcanoes, life on the planet would have to stay around the hydrothermal vents of the ocean. The final Ice Age of the Proterozoic marked the end of this eon and the beginning of the Cambrian Era.
Many land masses at this point were conjoined into one large supercontinent, called Rodinia. By the end of the Proterozoic Eon, these land masses were starting to detach from each other due to a severe glaciation.
Many geologists believe the Proterozoic Earth was covered in glaciers for several million years. Others believe the glaciations happened at least twice during the Proterozoic, once in the beginning and once in the end. Until the Earth warmed up due to carbon dioxide being released from volcanoes, life on the planet would have to stay around the hydrothermal vents of the ocean. The final Ice Age of the Proterozoic marked the end of this eon and the beginning of the Cambrian Era.