Where is Water Coming from?

by Michael Mascha

In the usual answer to the question where the water is coming from one tends to think about sky and the ground below us as the source of water. This is represented in the all familiar closed and loss-less Water Cycle of evaporation, condensation, precipitation and collection. But the Water Cycle mainly addresses the issue on how the water is recycled on our planet not the issue of inventory..

We are the blue planet and the signature for life on our planet is water, but where is the water coming from?

Recent discoveries in astrophysics point to water not being a natural terrestrial product but imported from our solar system. Ice, trapped in small comets, is probably the source of water on our planet.

The Earth is believed to have formed hot and dry, meaning that its current water content must have been delivered after the planet cooled.

This water is thought to have been first delivered here over 4 billion years ago. In a  period of celestial assault, when the moon became most heavily pock-marked, the Earth received 500 times more ‘hits’ and having a greater critical mass was also able to hold much the water (ice).

Large amounts of water are now believed to be lost as subduction of continental plates carries oceanic water under the surface. This water was thought to be recycled to the surface by outflow of gases from volcanic activity, but the losses are 7 to 20 larger than the outflow.

It is estimated that around 10 million small comets impacting our atmosphere still each year, with each comet containing 20–40 tons of water. This leads to significant input of water over time and it balances the earth water inventory offsetting the losses due to subduction.

The significance of the small comets and the ice they contain is obvious: our Earth would be dry and barren without an extraterrestrial influx of water.

Resources: Small Comets and Our Origin by Dr. Louis A. Frank