Dihydrogen in the context of "Standard conditions"

The prebiotic atmosphere is the second atmosphere present on Earth before today's biotic, oxygen-rich third atmosphere, and after the first atmosphere (which was mainly water vapor and simple hydrides) of Earth's formation. The formation of the Earth, roughly 4.5 billion years ago, involved multiple collisions and coalescence of planetary embryos. This was followed by an over 100 million year period on Earth where a magma ocean was present, the atmosphere was mainly steam, and surface temperatures reached up to 8,000 K (14,000 °F). Earth's surface then cooled and the atmosphere stabilized, establishing the prebiotic atmosphere. The environmental conditions during this time period were quite different from today: the Sun was about 30% dimmer overall yet brighter at ultraviolet and x-ray wavelengths; there was a liquid ocean; it is unknown if there were continents but oceanic islands were likely; Earth's interior chemistry (and thus, volcanic activity) was different; there was a larger flux of impactors (e.g. comets and asteroids) hitting Earth's surface.

Studies have attempted to constrain the composition and nature of the prebiotic atmosphere by analyzing geochemical data and using theoretical models that include our knowledge of the early Earth environment. These studies indicate that the prebiotic atmosphere likely contained more CO₂ than the modern Earth, had N₂ within a factor of 2 of the modern levels, and had vanishingly low amounts of O₂. The atmospheric chemistry is believed to have been "weakly reducing", where reduced gases like CH₄, NH₃, and H₂ were present in small quantities. The composition of the prebiotic atmosphere was likely periodically altered by impactors, which may have temporarily caused the atmosphere to have been "strongly reduced".

Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: dinitrogen (N₂), carbon monoxide (CO), dihydrogen (H₂), and carbon dioxide (CO₂). This is achieved by reacting the feedstock material at high temperatures (typically >700 °C), without combustion, via controlling the amount of oxygen and/or steam present in the reaction. The resulting gas mixture is called syngas (from synthesis gas) or producer gas and is itself a fuel due to the flammability of the H₂ and CO of which the gas is largely composed. Power can be derived from the subsequent combustion of the resultant gas, and is considered to be a source of renewable energy if the gasified compounds were obtained from biomass feedstock.

An advantage of gasification is that syngas can be more efficient than direct combustion of the original feedstock material because it can be combusted at higher temperatures so that the thermodynamic upper limit to the efficiency defined by Carnot's rule is higher. Syngas may also be used as the hydrogen source in fuel cells, however, the syngas produced by most gasification systems requires additional processing and reforming to remove the contaminants and other gases such as CO and CO₂ to be suitable for low-temperature fuel cell use, but high-temperature solid oxide fuel cells are capable of directly accepting mixtures of H₂, CO, CO₂, steam, and methane.