Water, in its purest form, is typically a poor conductor of electricity. This is because it lacks a significant number of charge carriers, which are necessary for electrical conductivity. However, when water is sprayed or atomized into microdroplets, a fascinating phenomenon occurs. These tiny droplets, due to contact electrification, can become charged. When oppositely charged water droplets come into close proximity, they can discharge electricity, emitting light in the process.
This unexpected luminescence, known as “microlightning,” offers a window into understanding how water droplets can cause chemical reactions, including the synthesis of organic molecules. These reactions could provide a plausible mechanism for the formation of life’s building blocks on early Earth, according to researchers in a new paper in Science Advances.
Water droplets typically carry a charge when they are formed or disrupted. This charge is the result of a process called contact electrification, which occurs when water droplets come into contact with another surface, such as air or an insoluble mineral. A common observation is that smaller droplets tend to carry a negative charge, while larger droplets become positively charged. This charge separation happens due to the shear forces that act on the droplets during the splashing or spraying process.
The unique properties of water droplets extend beyond just carrying a charge. When oppositely charged droplets approach each other closely, the difference in charge can lead to an electrical discharge. This discharge is accompanied by the emission of light, similar to what is seen during a lightning strike. The phenomenon, known as microlightning, offers a new way to view the interaction between water droplets and gases in the atmosphere.
Microlightning: A Possible Spark for Life?
The energy from microlightning might have powered the chemical reactions that formed the basic building blocks for life on Earth. This theory is supported by findings where water, when sprayed as a fine mist—such as after a wave crashes on the shore—forms tiny, oppositely charged droplets. As these droplets come into close proximity, they generate an electrical discharge, accompanied by a tiny flash of light.
Researchers have discovered that when this microlightning occurs in the presence of certain gases, including nitrogen, methane, and carbon dioxide, the energy from the discharge can lead to the synthesis of organic molecules. Among the molecules synthesized are glycine, an amino acid that is a building block of proteins, and uracil, a key component of RNA. These findings mirror the famous Urey-Miller experiment from the 1950s, which demonstrated how organic molecules could form under conditions simulating early Earth’s atmosphere.
The electrical energy produced by microlightning is sufficiently intense to excite, dissociate, and ionize surrounding gas molecules, creating a reactive environment. When sprayed water microdroplets are introduced into a mixture of gases such as nitrogen (N₂), methane (CH₄), carbon dioxide (CO₂), and ammonia (NH₃), the electrical discharge generated by the oppositely charged droplets leads to the formation of organic molecules, including those that contain carbon-nitrogen (C─N) bonds. These molecules are crucial for life, as they form the backbone of many essential biological compounds, including amino acids and nucleotides.
The synthesis of these molecules occurs in less than 200 microseconds, illustrating how rapidly chemical reactions could occur in the presence of microlightning. The ability to form such molecules in these brief moments supports the idea that microlightning could have played a role in the prebiotic chemistry that led to the origin of life on Earth.
Implications for Early Earth and the Emergence of Life
The process of microlightning from sprayed water droplets offers a possible pathway for the abiotic formation of life’s building blocks. Unlike lightning, which is an unpredictable and intermittent phenomenon, water sprays are far more common in nature. As such, microlightning may have been a frequent and reliable source of energy that powered chemical reactions on early Earth, helping to form the basic organic molecules needed for life.
This process also emphasizes the unique reactivity at the gas-water interface, where the electrical discharges from oppositely charged water droplets create an environment conducive to chemical reactions. The ability of water droplets to create such an energetic environment through microlightning offers a plausible explanation for how life’s essential molecules—amino acids, nucleotides, and others—could have formed in the early Earth’s atmosphere.
