Hydrogen, which makes up three-quarters of all matter in the universe, played a crucial role in the emergence and survival of life on Earth. The young Earth had a high concentration of hydrogen due to geological and volcanic activity. Just as stars burn hydrogen to produce heat and light, early life forms, such as archaea, extracted energy from hydrogen through chemical reactions.
Archaea, a third form of life discovered in the 1970s alongside bacteria and eukaryotes, have thrived for billions of years by utilizing hydrogen gas. These microorganisms have special enzymes called hydrogenases that allow them to harvest energy from hydrogen, enabling them to survive in extreme environments. They can even use the minute amounts of hydrogen present in the air as an additional food source, aiding their survival during transport between hydrogen-rich environments.
Archaea are found in environments where no other life can survive, such as boiling hot springs with highly acidic water. In these harsh conditions, hydrogen is continuously formed from geothermal processes, which archaea consume to repair their bodies and grow. Some archaea live deep underground where there is no light or oxygen. They break down organic matter through a process called “hydrogen-forming fermentation” to produce hydrogen gas. To minimize their energy needs, some archaea form ultra-small cells and act as parasites, stealing organic matter from other microbes.
Another group of archaea known as methanogens live in the intestines of animals and produce methane by consuming hydrogen. Methanogens are responsible for a significant portion of human-caused methane emissions, particularly from cattle. Researchers are working on ways to inhibit the activity of gut methanogens to reduce these emissions. Methanogens also contribute to methane emissions from various sources such as termite mounds, thawing permafrost, and trees.
As societies aim to transition away from fossil fuels, there is potential to learn from archaea’s hydrogen economy, which has thrived for billions of years. Much of Earth’s hydrogen is found in water, and industries currently require expensive catalysts like platinum to extract and work with hydrogen. However, archaea produce biological hydrogen catalysts called hydrogenases that are more efficient and economical, as they don’t rely on precious metals and can function under a wider range of conditions.
Hydrogen not only holds promise for future energy solutions but also played a significant role in the history of life. The merger of an archaeal cell and a bacterial cell around two billion years ago led to the evolution of eukaryotes, the ancestors of animals, plants, and fungi. This merger allowed for more efficient exchange of hydrogen gas, supporting the theory known as “the hydrogen hypothesis.” While most modern eukaryotes, including humans, have lost the ability to use hydrogen, traces of ancient archaea and bacteria still exist within our cells.
In summary, hydrogen has been a fundamental element in the emergence and complexity of life on Earth, and studying archaea’s use of hydrogen can provide insights for future energy solutions.
