Meteoric water

Meteoric water, derived from precipitation such as snow and rain, includes water from lakes, rivers, and ice melts, all of which indirectly originate from precipitation. The journey of meteoric water from the atmosphere to the Earth's surface is a critical component of the hydrologic cycle. While a significant portion of this water reaches the sea through surface flow, a considerable amount gradually infiltrates the ground, continuing its descent to the zone of saturation and becoming an integral part of groundwater in aquifers.

Most groundwater is, in fact, meteoric water, with other forms like connate water and magmatic (juvenile) water playing minor roles. Connate water, trapped in rock strata at the time of their formation and often saline due to its origins in ocean sediments, and magmatic water, which accompanies magma intrusion from great depths and influences mineralogy, contrast with meteoric water's journey through porous and permeable layers, including bedding planes and fractures.

Properties and Significance
Meteoric waters are distinguished by their minimal salinity and their initial acidity, characteristics that change based on their interactions with subsurface environments. The acidity of meteoric water, driven by atmospheric contributions of humic, carbonic, and nitrous acids, plays a critical role in the geochemical processes of soil and subsurface environments. As these waters percolate through soil and rock layers, especially carbonate rocks, their capacity to neutralize acidity influences the solubility of minerals, the availability of nutrients, and the transport of metals.

The Global Meteoric Water Line (GMWL) is a cornerstone concept in understanding the behaviour of meteoric waters. Established by Harmon Craig in 1961, the GMWL delineates the global annual average relationship between the isotope ratios of hydrogen and oxygen (oxygen-18 and deuterium) in natural meteoric waters. This isotopic signature is invaluable for tracking water masses in environmental geochemistry and hydrogeology, offering insights into water cycle dynamics, climatic conditions, and the origins of water samples.

History
The term "meteoric," referring to the direct atmospheric origin of this water, shares its root with the science of meteorology. It stems from a Greek word initially associated with astronomical phenomena. However, the scope of the term expanded significantly following the publication of Aristotle's "Meteorology." In this seminal work, which covers a broad range of earth sciences, Aristotle extended the term's application beyond astronomical discussions to include any significant phenomena observed in the sky, such as meteors, which were originally believed to be weather-related events.