Archean Eon Facts Revealed On Earth's History For Curious Kids

The Archean Eon is thought to be a time of volcanic eruptions and tectonic movements.

Archean Eon (also spelled Archaean Eon) was the second eon of Earth's history and it lasted from about 4-2.5 billion years ago. Archean rocks reveal that at this time, volcanoes were rapidly erupting as a result of the excessive heat inside Earth's crust.

Archean Eon is divided into three eras: the Early Archean, the Middle Archean, and the Late Archean. During this time, Earth's atmosphere and oceans formed, and primitive life began to evolve. Let's discuss some of the most interesting facts about Archean Eon!

What was the Archean Eon?

Archean Eon is known as the time in the history of Earth that came after the Hadean Eon. This eon not only had the first sedimentary rocks but also showed the first signs of existence of the first life forms. However, this eon did not provide the conditions for the sustenance of multicellular life.

This eon gives us some of the oldest rocks, and the fossils from the Archean Eon suggest the nature of the organisms that lived at this time.

For example, scientists have found through extensive research that the Stromatolites and Butterstones that have been found in places such as Bolivia and South Africa are proof of the life of some organisms such as blue-green algae called cyanobacteria.

Archean rocks also reveal how the continents formed. The formation of the first continent is said to have taken place during the Archean Eon as a result of rapid tectonic activity, as well as unfathomable volcanic eruptions. The existence of deep oceanic basins is also supported by the banded iron formations and chemical sediments.

The atmosphere of Earth consisted of methane, ammonia, and carbon dioxide at this time. There are some studies that reveal that in the presence of extreme heat, these gases could have reacted to form simple sugars and amino acids.

This study was held in the mid 20th century and provides considerable insight regarding the process through which Earth became what it now is. However, some of this research is not accepted in all the learned communities of the world.

Bacteria fossils recovered from chert beds help us in understanding the type of prokaryotes that existed at this time. It is assumed through banded iron formations that there was an eventual poisoning of a large chunk of such prokaryotes towards the end of this eon.

This is because there were huge amounts of free oxygen in the oceans, which not only created such iron formations but also threatened to remove prokaryotes such as cyanobacteria.

The Archean Eon was followed by the Proterozoic eon, which is also known as the era of hidden life. However, the earliest Archean findings remain of ultimate importance because the rocks reveal how the first continent was formed.

Eras Of The Archean Eon

The eras of Archean Eon are divided into Eoarchean (4.0–3.6 Ga), Paleoarchean (3.6–3.2 Ga), Mesoarchean (3.2–2.8 Ga) and Neoarchean (2.8–2.5 Ga). The era can thus be classified into the Early Archean, the Middle Archean, and the Late Archean. Each era was marked by specific changes on Earth.

Early Archean can be timed at around 4000-3600 million years ago. The Early Archean was a time of great change, as Earth's atmosphere and oceans formed and primitive life began to evolve.

The climate was much different than it is today, with high levels of carbon dioxide and methane in the atmosphere. There was no oxygen in the air, so life evolved under very different conditions than we are used to.

Middle Archean is estimated to have been around 3500-2800 million years ago. The Middle Archean saw the development of photosynthesis, which allowed life to thrive in the presence of oxygen. This era was also marked by the formation of Earth's first mountains and continents.

Late Archean, which was 2800-2500 million years ago, was a time of growth and change, as primitive life evolved into more complex forms. The atmosphere and oceans continued to evolve, and conditions were becoming more similar to those we see today. By the end of Archean Eon, Earth was starting to look like the planet we know today.

Because the Hadean, Archean, and Proterozoic eons are all included in the Precambrian era, it is the longest.

Characteristics Of The Archean Eon

The Archean period is known for its reducing atmosphere, the first oceans, volcanic activity, the formation of the first continents, rapid tectonic activity, and the appearance of the earliest life forms.

This period in the history of Earth is considered to be important in many studies because the first life forms that ever happened to have lived on Earth's crust, the prokaryotes, came into existence at a time when there was no free oxygen in the atmosphere.

The atmosphere of the Archean period was very different. The three dominant components of air during the Archean Eon were methane, carbon dioxide, and ammonia. In addition to this, liquid water was a common sight at this time.

Fossils from the Archean Eon show deep water sediments. These ancient sediments show signs of the rapid release of lava in its molten state and its quick solidification, which helped in Earth's formation.

Plate tectonics was also very common at this time, mainly because during the Archean Eon, the temperature of Earth's interiors was way higher than it is today. The same is also reflected through the Archean rocks.

What was the climate of Earth during the Archean Eon?

Climatic conditions during the Archean Eon were very different from what we are used to in the present day.

The Archean atmosphere was filled with greenhouse gases such as ammonia, methane, and carbon dioxide. There was no free oxygen in the air, and hence, the first forms of life that ever came into existence were anaerobic in nature. This essentially means that these organisms did not require oxygen for survival.

Apart from this, it is believed that Earth's interior was very hot at this time, which resulted in tectonic activity as well as volcanic eruptions. The volcanic sediments and island arcs of this time show that the formation of rocks and their recycling process was very rapid, mainly because of the internal condition of the planet.