3 ms·

> isn't Earth's H2O mainly circulating and, hence, 'old' in the sense that all molecules are? A lot of it may be, but some of it isn't. You can buy quartz, fo

> isn't Earth's H2O mainly circulating and, hence, 'old' in the sense that all molecules are? A lot of it may be, but some of it isn't. You can buy quartz, for example that contain water or petroleum sloshing around inside [1] although some think the water could seep in and out over time. But quartz with fluid inclusions (small bubbles containing water) are completely sealed and have the same composition as they were up to 3 billion years ago. "the fluid in the inclusion is an actual sample of fluid in which the mineral was growing" [2] [1] https://en.m.wikipedia.org/wiki/Enhydro_agate https://en.m.wikipedia.org/wiki/Enhydro_agate [2] https://www.gamineral.org/writings/enhydros-gray.html https://www.gamineral.org/writings/enhydros-gray.html

advantager 4y ago
To expand on this Groundwater "age" is typically considered in terms of residence time, that is the period of time between entering the subsurface and exiting at some discharge location. These analyses are often based upon the hydrogeochemistry and the decay rate of known isotopes, hence the mass spectrometer. Shallow, unconfined aquifers often contain "young" groundwater, on the order of decades or centuries. For example snow melts on a mountain, downhill into a flatter coarse grained area where it enters the groundwater system. The groundwater then moves downdip along the bedrock contour through and into the deeper alluvial basin, eventually naturally discharging into a river or is pumped out at a well. It would be interesting to read their paper to understand how they (i.e. what isotope) can date back to 1.6 billion years. https://books.gw-project.org/groundwater-in-our-water-cycle/part/groundwater-residence-time/ https://books.gw-project.org/groundwater-in-our-water-cycle/...

3 ms·

> isn't Earth's H2O mainly circulating and, hence, 'old' in the sense that all molecules are? A lot of it may be, but some of it isn't. You can buy quartz, fo

by teruakohatu 4y ago

advantager 4y ago
To expand on this Groundwater "age" is typically considered in terms of residence time, that is the period of time between entering the subsurface and exiting at some discharge location. These analyses are often based upon the hydrogeochemistry and the decay rate of known isotopes, hence the mass spectrometer. Shallow, unconfined aquifers often contain "young" groundwater, on the order of decades or centuries. For example snow melts on a mountain, downhill into a flatter coarse grained area where it enters the groundwater system. The groundwater then moves downdip along the bedrock contour through and into the deeper alluvial basin, eventually naturally discharging into a river or is pumped out at a well. It would be interesting to read their paper to understand how they (i.e. what isotope) can date back to 1.6 billion years. https://books.gw-project.org/groundwater-in-our-water-cycle/part/groundwater-residence-time/ https://books.gw-project.org/groundwater-in-our-water-cycle/...