Azoic

We explain what the azoic eon was, how it is divided and its characteristics. Also, its climate, its flora and its fauna.

What was the Azoic?

The earliest division of the geological time scale is known as Azoic, azoic eon or hadic eon.. It began about 4.5 billion years ago and ended 3.8 billion years ago, when the archaic eon began.

Their names come from ancient Greek: azoic means “without life” or “without animals” (to– and zoe), since this period is prior to the appearance of life on planet Earth; hadic, for its part, It refers to “hell” or “underworld”, since Hades was the name that the ancient Greeks gave to the kingdom of the dead.

The study of the Azoic is extremely difficult, since there are no fossil remains to find and most of the rocks from this time have changed over millions of years. One of the few minerals known to date from this time are zircon crystals.

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Characteristics of the azoic eon

The Azoic has the following characteristics:

• It is the oldest geological period.
• There is very little information about its geology and climate.
• Almost no rocks formed in this period are preserved.
• The atmosphere was at high temperatures and oxygen did not exist.
• The surface of the planet was not yet solid.
• There was no plant or animal life on Earth.
• It is the eon in which the only natural satellite of the Earth was formed: the Moon.

Division of the azoic eon

Given the few geological records that have survived from such early times, There is no proposal for subdivisions for the Azoic. In fact, it is the only aeon that has no internal divisions. Everything that happened more than 3.8 billion years ago is simply considered part of it.

Geology of the azoic eon

During the Azoic Eon, the Earth was formed from the accretion (collision and aggregation) of materials present around the newly formed Sun. This process produced heating of the planet in formation, due to the energy released by the impacts. As a consequence, the Earth was not solid during the initial stages of this eon, but was composed primarily of molten materials.

As time passed and the planet cooled, the inner layers of the Earth began to form. In this process, iron and other dense metals sank toward the center of the planet and formed the core, while lighter materials rose to form the mantle and crust. This led to the release of large amounts of gases, which contributed to the formation of the early atmosphere. Additionally, volcanic activity was intense during the Azoic Eon, with frequent eruptions that released gases such as carbon dioxide, water vapor, ammonia, and methane. These also collaborated in the composition of the first atmosphere.

Likewise, during the Azoic, the Moon was formed as a result of an impact between the forming Earth and a celestial body the size of Mars.

The formation of the Moon

The Moon is believed to have formed about 4.5 billion years ago, from the remains of a collision between the early Earth and a Mars-sized object, known as Theia.

Upon collision, the cores of both objects fused, but left a scattered ring of debris floating around. These would have given rise to two natural satellites, one of which crashed into Earth again. The other satellite remained at the distance necessary to orbit around it and today is known as the Moon.

The oldest rocks in the world

The oldest minerals on the planet have been found in the sedimentary region of western Canada and in the Jack Hills region of western Australia.

In both cases, they are individual zircon (or zircon) crystalsa mineral composed of zirconium silicates (ZrSiO₄), translucent in appearance and variable color. Currently, the main deposits are located in Australia, South Africa, India, Brazil and the United States.

Climate of the azoic eon

The Earth’s atmosphere in the Azoic period was composed of carbon dioxide, water vapor, ammonia, methane, and other volatile gases.. Oxygen was non-existent. In addition, the young Earth was subject to intense volcanic activity: the continuous release of gases during eruptions kept the atmosphere very hot.

Likewise, during the Azoic, the Earth was frequently impacted by celestial bodies of various sizes. These impacts released thermal energy that also heated the atmosphere.

As the Earth gradually cooled, water vapor in the atmosphere began to condense, leading to the formation of the first bodies of liquid water.

Flora and fauna of the Azoic eon

During the Azoic Eon, the Earth was in a highly unstable and extreme state, with very high temperatures due to the accumulation of internal heat generated by planetary formation and intense volcanic activity. These conditions were not conducive to the existence of animal or plant life..

Only towards the end of the Azoic, with the formation of the first bodies of water, would the ecological conditions necessary for the appearance of life begin to be generated. The first recorded bacteria date from the following eon, the Archean.

References

• The Geological Eras. (sf). The geological eras of the Earth on the time scale. https://laserasgeologicas.com/
• Tarbuck, E. and Lutgens, F. (2005). Earth Sciences. An introduction to physical geology. Pearson Education.