Chemical Evolution and the Origins of Life on Earth

Formation of Essential Molecules on Early Earth

Carbon bonded to four hydrogen atoms creates the molecule methane; nitrogen combined with three hydrogen atoms creates ammonia; and oxygen combined with two hydrogen atoms forms a molecule of water.

The Process of Organic Synthesis

The first organic compounds that formed were similar to those currently required by the simplest living cells. These compounds include:

• Sugars
• Fats
• Nucleic acids
• Proteins

Stanley Miller and the First Synthesis

In 1953, Stanley Miller presented a paper entitled "First Synthesis," detailing organic compounds obtained in the laboratory under supposed primitive Earth conditions.

To prove his point, he created an experiment in which he recreated the primitive atmosphere of the Earth in a flask and subjected it to severe electrical shocks. After a week of analyzing the reaction products, he found that organic compounds were synthesized—in particular, amino acids (e.g., alanine)—from which proteins and key components of organic matter are formed.

Miller had managed to form organic compounds in pre-biological conditions; that is, under conditions that existed on Earth prior to the appearance of life!

Melvin Calvin and High-Energy Synthesis

In 1961, Melvin Calvin was among the first to use a cyclotron as an energy source. From a combination of primitive gases (such as methane) and a carbon framework with radioactivity, Calvin achieved the synthesis of amino acids, sugars, urea, fatty acids, and other organic compounds by exposing the mixture to a flow of electrons accelerated at high speed by the cyclotron.

Joan Oró and the Synthesis of Adenine

In 1960, Joan Oró included the reactions that can occur when hydrogen cyanide reacts with ammonia. By mixing these two gases with water and heating the solution, he obtained adenine, an essential compound in nucleic acids.

Sidney Fox and Thermal Proteinoid Microspheres

Based on the coacervates of Oparin, Sidney Fox demonstrated that thermal proteins form microspheres with a diameter more or less similar to a bacterial cell. These microspheres, like coacervates, are separated from the external environment by a surface layer.

As living cells, they possess osmotic properties. These cells can break their functioning and reach a critical size.

Feeding Mechanisms of the First Organisms

The Heterotrophic Hypothesis

Heterotrophs are organisms that eat others. Presumably, when the first forms of life originated from non-living matter, they were incapable of developing their own food. Therefore, most primitive bodies had a simple metabolic system that was soon perfected. Over time, this led to more evolved and, therefore, more complex metabolism.

The Evolution of Heterotrophic Organisms

Certain reactions favored the dynamic stability of these bodies, while others were destroyed. Only those that possessed internal chemical reactions and a favorable molecular organization could survive.