We explain what the Precambrian was, the stages into which it is divided and how the Earth was formed. Also, what are its characteristics and how life appeared on the planet.
The Precambrian lasted approximately 3,960 million years.
What was the Precambrian?
The Precambrian is known as the first and longest stage in the history of the Earth.This is an eon that lasted approximately 3,960 million years and ended about 540 million years ago, with the beginning of the Phanerozoic eon and its first era, the Paleozoic. Its beginning coincides with the origin of the planet, around 4,500 million years ago, and its duration covers a large part of geological history.
In the Precambrian eon the planet was formed, the first geological events began and life on Earth began.Despite its importance, studying the Precambrian is difficult, given that there are almost no fossil records that have survived to the present day and the rocks formed in those periods have changed considerably over billions of years of transformation.
Characteristics of the Precambrian
The main characteristics of the Precambrian are:
- It began 4.5 billion years ago, with the formation of the planet.
- It lasted 3.96 billion years, which represents 88% of the Earth’s geological history.
- It ended 540 million years ago, with the beginning of the Phanerozoic eon.
- It is subdivided into three eons: the Hadean, the Archean and the Proterozoic.
- The temperature of its atmosphere was very high at first, and it cooled as time went by.
- The cooling of the Earth allowed the formation of the first rock structures.
- It is the eon in which water and the first forms of life appear on the planet.
Precambrian Division
The Precambrian eon is further subdivided into three other eons:
- hadic aeonIt is the oldest and began with the formation of the Earth 4.6 billion years ago. It is not subdivided into geological eras.
- Archean EonIt began 3.8 billion years ago and is subdivided into three eras:
- It was paleoarchaic. It began 3.8 billion years ago and lasted 400 million years.
- Mesoarchic era. It began 3.4 billion years ago and lasted 400 million years.
- Neoarchaic era. It started 3 billion years ago and lasted 500 million years.
- Proterozoic EonIt began 2.5 billion years ago and ended 540 million years ago. It is subdivided into three eras:
- Paleoproterozoic era. It began 2.5 billion years ago and lasted 900 million years.
- Mesoproterozoic era. It began 1.6 billion years ago and lasted 700 million years.
- Neoproterozoic era. It began 900 million years ago and lasted 360 million years.
The formation of planet Earth
The nebular hypothesis holds that the Earth was formed from a cloud of dust and gases.
There are many theories about how our planet and solar system were formed. The most accepted ones assume that it was a process of sedimentation and stabilization of the same matter of which the Sun is composedor matter produced during its birth, initially gathered in a planetesimal disk (young stars that begin to form as planets), just over 4.5 billion years ago.
According to this theory, known as the “nebular hypothesis”, our planet was formed from a cloud of dust and gases that began to attract each other due to gravity.Over time, planetesimals would have condensed enough to have a material existence and a defined form. This is how the planet Earth and the rest of the solar system would have formed.
Geological characteristics of the Precambrian
Cratons began to form on a mantle of molten rock.
The Earth is believed to have formed approximately 4.6 billion years ago from the material surrounding the Sun.. At first, it was a hot ball of molten minerals, due to the accumulation of energy during the formation process.
As the Earth cooled, the crust began to solidify, forming a more rigid outer layer over the molten core.. Thus, due to the solidification and cooling of the crust, a gradual process began in which cratons were formed, which are stable and rigid areas of the Earth’s crust that can be considered precontinental cores.
The process of convergence and collision of cratons was fundamental to understanding the formation of continents. As these cratons moved and collided, accumulations of material were created that eventually became the cores of the continents.. The oldest rock formations, called shields or massifs, appeared during the Archean eon, approximately 3.5 billion years ago.
Precambrian climate
Initially, The temperature in the protoatmosphere, made up mainly of water vapor, carbon dioxide, sulfur, ammonia and nitrogen, was extremely high. However, terrestrial volcanic activity expelled large amounts of carbon dioxide and water vapor, which gradually cooled the planetary temperature to reach 100 ° C about 3.8 billion years ago.
Only then did liquid water begin to form, which gave rise to the proto-oceans. Thus began the first general cooling of the planet, until in the Proterozoic eon (especially in the Neoproterozoic geological era, in the cryogenic period), There was a cooling with significant drops in temperature and the appearance of the first glaciations.
Volcanic activity
Volcanic activity was very important during the early stages of the Precambrian. The volcanoes of that period, much larger and more active than those of today, spewed large quantities of lava that, when cooled, thickened the Earth’s crust.
Thus, Precambrian volcanic events not only shaped Earth’s geography, but also influenced the chemistry of the atmosphere and oceans. The emission of volcanic gases, such as carbon dioxide and water vapor, played an important role in regulating the climate and in the formation of the first oceans. In addition, volcanic activity released essential elements and minerals that contributed to the development of life.
The origin of life
The most widely accepted hypothesis is that life began on the planet approximately 4,280 to 3,770 million years ago.when water vapor began to condense and the first reserves of liquid water appeared.
The exact way in which life began is difficult to establish, but It is believed that it may have originated in microscopic bubbles formed in the oceans, which contained certain chemical elements. From these bubbles, more complex and functional structures were created, which even managed to replicate themselves. This is how the first protocells would have emerged, which launched evolution.
The Great Oxidation
The first bacteria were able to take advantage of sunlight.
The Great Oxidation Event began approximately 2.4 billion years ago, during the Proterozoic Eon.Before this event, the Earth’s atmosphere contained very low levels of oxygen, so that life existing at that time did not depend on oxygen for its metabolic processes.
The release of oxygen into the atmosphere occurred mainly as a result of the photosynthetic activity of cyanobacteria, which are microscopic organisms capable of carrying out photosynthesis. Through this process, these bacteria captured carbon dioxide from the atmosphere and released oxygen. As cyanobacteria proliferated, oxygen began to accumulate in the atmosphere and oceans. This process of substantial increase in oxygen due to photosynthetic activity was called the Great Oxidation Event..
Another consequence of the Great Oxidation was the formation of the ozone layer in the stratosphere. The oxygen released by the cyanobacteria reacted with the Sun’s ultraviolet radiation and created ozone molecules, which formed a protective layer around the Earth. This ozone layer began to block much of the harmful ultraviolet radiation, allowing different forms of life to colonize surface waters and land without being subjected to lethal levels of radiation.
The Great Oxidation Event also had a profound effect on biological evolution.since the increasing availability of oxygen allowed the development of aerobic organisms, that is, those that depend on oxygen to live.
References
- AstroMía. (sf). Geological history: the Precambrian. https://www.astromia.com/
- Tarbuck, E. and Lutgens, F. (2005). Earth Sciences. An Introduction to Physical Geology. Pearson Education.
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