Deep orange or reddish-brown atmosphere: The second atmosphere’s formation was crucial and occurred just before or alongside the formation of Earth’s oceans, which directly supported the evolution of organic molecules and prebiotic microenvironments. The second atmosphere began to develop around 4.5 to 4 billion years ago, as volcanic outgassing released gases trapped in the Earth’s […]

Likely white or grayish atmosphere: The first atmosphere developed first but was not directly involved in the development of life. The first atmosphere formed shortly after Earth’s formation around 4.5 billion years ago. This initial atmosphere was primarily composed of hydrogen and helium, the lightest and most abundant elements in the universe, which were captured from

As the Earth cooled following its formation, outgassing from volcanic activity released water vapor and other gases into the atmosphere. When the Earth’s surface cooled sufficiently, this water vapor condensed and fell as rain, filling the basins that would become oceans.

The chemical evolution from inorganic precursors to organic molecules is a fascinating story of transformation driven by Earth’s dynamic early conditions and possibly assisted by the input from space in the form of meteorites rich in organic compounds. During this period, the Earth witnessed a series of complex chemical reactions facilitated by its primordial atmosphere,

Following the appearance of self-replicating molecules, the RNA world hypothesis suggests a period where RNA served both as genetic material and as a catalyst for chemical reactions. This phase emphasizes the central role of RNA in early life forms, prior to the evolution of DNA and proteins. The RNA world could be considered both a

Between the development of metabolic pathways and the formation of cellular membranes, there might have been a phase involving the assembly of protocells. These protocells, formed from self-assembled lipid molecules creating vesicles, could encapsulate nucleic acids and metabolic molecules, offering a primitive model for cell-like structures. Protocells represent a bridge between non-living chemical systems and

Alongside or following the chemical evolution of organic molecules, the formation of prebiotic microenvironments, such as hydrothermal vents or warm little ponds, provided niches where concentrations of organic molecules could interact. These environments could have been crucial for the assembly of complex organic molecules and the initiation of catalytic cycles.

While the 4.4 billion years ago is a guess as to when these processes might have started, the 4.1 billion years ago guess is a better representatoin of current understanding on when the needed building blocks of life evolved. Before the appearance of self-replicating molecules, there was a crucial phase of chemical evolution where simple

The formation of cellular membranes represents a pivotal development in the pre-life world, enabling the creation of defined boundaries for primitive cells. These membranes, likely formed from simple lipid bilayers, provided a controlled environment for chemical reactions and played a critical role in the emergence of the first cell-like structures, distinguishing them from their surrounding

Before the diversification of life, the establishment of basic metabolic pathways marked a crucial step towards biochemistry that supports life. These pathways allowed the conversion of inorganic and simple organic molecules into more complex compounds, setting the stage for energy transfer and the synthesis of key biomolecules necessary for cellular processes.

First Prokaryotes: They evolved from replicating molecules and before LUCA (also a prokaryote). Prokaryotes lack a nucleus and organelles. Although research continues identifying when the first true prokaryotes evolved, it is believed they evolved sometime between 3.8 to 4 billion years ago. While the earliest prokaryotes are part of our direct-line ancestors, today we know