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Whether or not we can swim in water depends (in part at least) on its pH.
If you regular visit a swimming pool, you’ll be reassured to know that behind the scenes, staff are regularly testing its pH levels. Anything between 7.2 and 7.8 is acceptable for swimming, with 7.4 being the optimal pH for human swimmers in a pool – only slightly above pH 7 of neutral water.
Outside of that range, the water could cause skin irritation (and if the range was more extremely acidic or alkaline, much worse could happen too).
So it follows that seawater must be swimmable too – since we regularly do take a dip in it.
With a global average pH of 8.1 ocean water is slightly alkaline. But the good news is that our bodies can handle it – unsurprising since the uterine fluid that we grow in ranges from neutral to slightly alkaline.
And for sea creatures too, a slightly alkaline water is perfect for their existence, with marine ecosystems evolving over time with adaptions to suit the ever-so-slightly alkaline water.
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What’s more, aside from its salt content, sea water would be considered safe for drinking, just like pool water would.
However, neither should be consumed in large quantities, due to the salt in the former and the chemicals in the latter.
But humans can safely drink anything from pH 6.5 to 9.5, meaning that any clean water ranging from very slightly acidic to a little alkaline is okay for consumption.
With this in mind, it’s easy to see how the water on our planet has supported life (as a source of hydration and a habitat) for millions of years.
It hasn’t always been this way though.
By observing our 4.5 billion year old planet’s ocean acidity over the course of its lifetime, scientists based at Yale and in Singapore have embarked on a NASA part-funded study to determine when and how our planet became capable of supporting life.
And their new theoretical model, recently presented in a paper in the journal Nature Geoscience, proves that our now alkaline ocean waters were once acidic, posing one of the biggest challenges to Earthly habitability.
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Why was our planet unable to sustain life with acidic seawaters?
Well, it’s difficult for organic molecules to synthesise in acidic conditions – that’s why agar, the culture medium typically used in a petri dish, has a pH between 7.1 and 7.5.
Thus, to understand exactly when the Earth became capable of supporting and sustaining life, scientists needed clarity on when oceanic waters verged toward neutral, and then alkaline. As Meng Guo from Nanyang Technological University in Singapore explained in a Yale statement, this information was crucial to mapping billions of years of seawater change:
“To understand the origin of life, it becomes important to understand when and how Earth began hosting an ocean with a more neutral pH.
But modeling the long-term evolution of ocean pH is a notoriously difficult problem, as it involves almost all of the components of the Earth system: the atmosphere, the ocean, the crust, and the mantle.”
Over time, the team’s model showed just how the pH of our planet’s oceans changed over time – how earth and environmental factors changed the seas, and why our oceans are getting a little less alkaline now, as the statement continues:
“Ocean pH depends to a large extent on atmospheric carbon dioxide (CO2), which, in turn, is influenced by a variety of other factors. The concentration of CO2 decreases, for instance, as a result of its chemical reaction with continents, deep-sea oceanic crust — and its eventual plunge into Earth’s interior via subduction. But levels of atmospheric CO2 increase when there is volcanic activity.”
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So what exactly did they find?
Well, according to the models, the research team concluded that it took our planet over 500 million years to neutralize the acidity that was once present in our oceans.
Only when the ocean became neutral was life truly able to exist and flourish on Earth, adapting over billions of years as the planet’s natural geological and atmospheric processes eventually made its marine habitats more alkaline.
This is vital research, Yale’s Professor Jun Korenaga explained in the statement, both in terms of understanding our planet’s past, and comprehending what could happen in its future:
“This is a tour-de-force theoretical endeavor, bridging a longstanding gap between surface processes and processes deep in the Earth. This work presents by far the most comprehensive whole-Earth system model to estimate how ocean pH likely evolved during Earth’s history.”
However, new understanding of oceanic pH comes with a warning. Before the Industrial Revolution, our ocean averaged at a pH of 8.2, but nowadays they are 8.1. This was a result of the increased level of carbon dioxide that our species suddenly began releasing into the atmosphere.
Any pH change – however small it sounds – can be detrimental to marine ecosystems that have adapted to long-established water conditions.
Given the importance of many aquatic organisms like phytoplankton to the health of our planet, it is vital that we support climate-focused measures to reduce our carbon emissions and protect our planet before it’s too late.
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