Iron–sulfur world hypothesis

The iron–sulfur world hypothesis is an idea about how life first began on Earth. It was suggested by a man named Günter Wächtershäuser, who was a patent lawyer from Munich but also studied chemistry. He shared his ideas in several articles between 1988 and 1992, after philosopher Karl R. Popper encouraged him.

This hypothesis suggests that the very first living things might have started growing on the surface of special minerals called iron sulfide. These minerals are important because they contain iron and sulfur, two elements that are key parts of many processes in living cells today.

Wächtershäuser developed his idea by looking at how life works now and then thinking backwards. He used what we know about chemistry to imagine how life could have begun a very long time ago. He also did experiments to test his ideas, trying to see if simple chemicals could form the basic building blocks of life under conditions similar to those on the early Earth.

Origin of life

The iron–sulfur world hypothesis suggests that the earliest form of life began in a hot, pressured volcanic environment. This first life form, called the "pioneer organism," was made of minerals, especially iron and nickel, which helped turn simple gases into more complex organic compounds. These minerals acted like tiny helpers, making it easier for important chemical reactions to happen.

This hypothesis also talks about how simple nutrients could change into more useful forms. For example, it explains how water and gases in volcanic areas could create new compounds. The idea is that these early chemical reactions, helped by minerals, slowly built up the basic parts of life we know today.

Early evolution

Further information: Abiogenesis

Early evolution is the time from when life first began until the last universal common ancestor (LUCA) lived. The iron–sulfur world theory says this time includes the growth of cells, the development of our genetic code, and the creation of important chemical processes.

Cells may have started with simple fats called fatty acids forming on minerals. These fats then helped create thin layers around these minerals. Over time, these layers grew into closed cells. These early cells could share genetic material often, which helped life evolve quickly. Important chemicals needed for life, like those used in breaking down food, can form without help from special molecules. Experiments also show that important building blocks for life, like amino acids and parts of DNA, can form under conditions found near deep-sea vents.

William Martin and Michael Russell think the first cells may have formed inside special deep-sea vents called alkaline hydrothermal vents. These vents have tiny spaces with walls made of minerals. These spaces could gather important chemicals and create the right conditions for life to start. The flow of water in these vents provided energy and building blocks for life. This model suggests LUCA lived inside these vent structures before moving out. The final step would be making a fat layer around the cell, allowing it to live independently. This idea matches what we see in modern cells, which have different types of fats in their membranes.

Alternative environment

Scientists think early life might have started in special areas called hydrothermal fields. These places had lots of metals and were very acidic, which helped simple molecules come together. The changing temperatures in these fields helped important chemical reactions happen, like making RNA, a molecule that carries instructions for life.

These fields also had wet and dry cycles, which helped molecules stick together. This could have allowed early cells to share materials, kind of like how modern cells share genes. Some scientists think these places were similar to what Charles Darwin imagined as a "warm little pond" for life to begin. However, there are some problems with this idea, like the chemistry not matching what we know about life today.