Archaeon Eon

Archaean Eon

4,000 to 2,500 Ma

What organisms lived during this time?

The Archaean Eon saw the emergence of life on Earth. The first life forms were simple, single-celled microorganisms, including bacteria and archaea.These early life forms are often referred to as extremophiles because they thrived in extreme conditions, such as high temperatures, acidic environments, and areas with little or no oxygen.

Interesting Facts about the Archaean Eon

• Ancient Fossils: The Archaean Eon is associated with some of the oldest known fossils on Earth. Fossils of stromatolites, microbial mats created by cyanobacteria, provide evidence of life dating back more than 3 billion years.
• Long Duration: The Archaean Eon lasted for approximately 1.5 billion years, making it a substantial portion of Earth's history. This eon was longer than all of Earth's subsequent eons (the Proterozoic, Phanerozoic, and Hadean Eons) combined.
• Early Life's Resilience: Despite the harsh conditions of the early Earth, some microorganisms in the Archaean Eon were remarkably resilient. They could thrive in extreme environments, including hot springs, acidic lakes, and hydrothermal vents.
• A Precarious Balance: The oxygenation of the atmosphere was not a linear process. At several points during the Great Oxygenation Event, oxygen levels rose and fell in a seesaw fashion due to interactions between oxygen-producing and oxygen-consuming processes. This created an unstable and sometimes toxic environment for early life forms.

What was the world like (the climate or the atmosphere)?

The atmosphere during the Archaean Eon was vastly different from today. It consisted mainly of gases like methane (CH4), ammonia (NH3), and water vapor (H2O), with very little oxygen (O2). This type of atmosphere is often referred to as a reducing atmosphere. The climate was significantly hotter than today, with higher temperatures due to the absence of oxygen and the greenhouse effect caused by the high levels of methane in the atmosphere.

The Great Oxygenation Event

Transition to an Oxidizing Atmosphere

Oxygen Accumulation in Oceans

Emergence of Cyanobacteria

Oxygen Breakthrough

Formation of the Oxygen Oasis

Mass Extinctions

Modern Oxygen Levels

Impact on Evolution