Hot springs may have played a key role in the emergence of life

One of the most enduring scientific mysteries concerns the origins of life on Earth. Researchers have often focused on the potential role of deep-sea hydrothermal vents – towering underwater structures that release a mixture of organic and inorganic materials. 

Within the plumes of these vents are minerals known as iron sulfides, which scientists believe may have catalyzed early chemical reactions essential for life.

Hot springs and the emergence of life

Interestingly, these same minerals are also found in modern hot springs, such as the Grand Prismatic Spring in Yellowstone National Park. These springs are created by groundwater heated through volcanic activity beneath the Earth’s crust.

New research led by an international team of scientists and published in the journal Nature Communications contributes to the growing body of evidence suggesting that ancient hot springs may have played a critical role in the emergence of life. 

This work helps to reconcile competing theories about the environments where life could have first arisen.

From geochemistry to biology

Carbon fixation, a fundamental process for life, involves converting carbon dioxide from the air or water into organic molecules. 

Various life forms, including plants, bacteria, and archaea, accomplish this through distinct pathways, with photosynthesis being a well-known example.

Each carbon fixation pathway is a series of enzyme-driven reactions, some of which involve proteins with iron-sulfur cores. These iron-sulfur clusters are present in all life forms and are believed to trace back to the Last Universal Common Ancestor – a cell proposed to be the origin point for all life on Earth.

Minerals in land-based hot springs 

Iron sulfides, formed when dissolved iron reacts with hydrogen sulfide gas, exhibit structures remarkably similar to these iron-sulfur clusters. 

This resemblance has led some scientists to hypothesize that iron sulfides were key in bridging the gap between Earth’s geochemical conditions and biological processes.

The new research extends this understanding by exploring the chemical properties of iron sulfides in ancient land-based hot springs, which share similarities with deep-sea hydrothermal vents.

Simulating early Earth’s hot springs

To replicate early Earth’s hot spring conditions, researchers designed a custom chamber. Inside, synthesized iron sulfide samples – some pure and others mixed with common hot spring metals – were spread across the chamber. 

A lamp simulated sunlight on Earth’s ancient surface, with varying levels of ultraviolet radiation.

Carbon dioxide and hydrogen gas, known to be important for carbon fixation in deep-sea vent experiments, were continually pumped into the chamber. 

Hot springs and early life processes 

The results showed that all the iron sulfide samples were capable of producing methanol, a simple organic molecule, though production levels varied. 

These findings indicate that iron sulfides can facilitate carbon fixation in both deep-sea vents and terrestrial hot springs.

Methanol production increased when the samples were exposed to visible light and higher temperatures. 

Additional experiments with different temperature ranges, lighting conditions, and water vapor content further demonstrated that land-based hot springs could have supported carbon fixation processes on early Earth.

Uncovering an ancient pathway

Further experiments and theoretical analyses revealed that methanol production occurred through a reaction called the reverse water-gas shift. 

This reaction mirrors part of the acetyl-CoA (or Wood-Ljungdahl) pathway, a method used by some bacteria and archaea to convert carbon dioxide into energy-rich molecules. The acetyl-CoA pathway is thought to be one of the earliest mechanisms for carbon fixation in life.

What makes this connection fascinating is that the reverse water-gas shift takes place on dry land near hot springs, while the acetyl-CoA pathway occurs in the aqueous environment of living cells. This parallel suggests a shared origin for these processes, bridging the gap between geochemistry and biology.

The study demonstrates that methanol production could occur under a wide range of conditions similar to those found in early Earth’s hot springs. 

These results broaden our understanding of how iron sulfides may have facilitated the chemical reactions necessary for life, both in the ocean and on land.

Implications for life’s origins

This research supports the prevailing scientific consensus that iron-sulfur clusters and the acetyl-CoA pathway are ancient and may have been crucial in the emergence of life. 

By showing that carbon fixation is possible in both marine and terrestrial environments, the findings highlight the versatility of early chemical processes.

Whether life began at the bottom of the ocean or at the edges of hot springs on land, this study underscores the importance of iron sulfides in the origin of life. 

The research also provides a framework for understanding how life might arise in similar conditions on other planets, offering valuable insights into the universal principles of life’s origins.

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