Why is ocean salinity not a good chronometer?

Why the Ocean’s Saltiness Can’t Tell Time

Ever wonder if you could use the ocean’s saltiness like a giant clock, ticking away the Earth’s age? It’s a neat idea, right? The concept is straightforward enough: rivers constantly wash dissolved salts into the sea. So, in theory, measure how quickly the ocean gets salty, and voilà, you’ve got an estimate for how long the Earth’s been around. Sounds simple, but trust me, it’s anything but. Ocean salinity as a chronometer? Not so fast. The ocean’s a far more complicated beast than that, a swirling soup of ever-changing influences that make it a terrible timekeeper.

The “Salty Clock” – A Beautifully Flawed Idea

This whole “salinity clock” idea rests on a few assumptions, and that’s where things fall apart. You see, these assumptions just don’t hold water (pun intended!) when you zoom out to look at the big picture, the geological timescale:

• Constant River Flow? Nope. The amount of salt rivers dump into the ocean isn’t some steady drip. It’s more like a feast or famine situation, depending on all sorts of things. Think about it: when mountains are forming, you get way more weathering and erosion, which means more salt washing into the sea. And volcanic eruptions? Forget about it – even more stuff gets dissolved and carried away i.
• Salt Always Stays Put? Guess Again. Salt doesn’t just hang around in the ocean forever. Nope, it gets taken out, too, but not in a consistent way. Ever heard of evaporites? These are massive salt deposits that can form when seawater evaporates in huge quantities, like in shallow seas. This process alone can suck up massive amounts of salt, throwing off our “clock” completely i. Plus, there’s subduction. This is where the Earth’s crust dives back into the mantle, taking chlorine with it i.
• Starting from Scratch? Wishful Thinking. Trying to figure out the ocean’s original saltiness is like trying to find a needle in a haystack. We simply don’t know what the early ocean was like. Some studies even suggest it might have been twice as salty as it is today i! Imagine trying to set a clock when you don’t know where the hands started.
• A Sealed Jar? Not Even Close. The ocean isn’t some closed-off container. It’s constantly interacting with everything around it – the air, the land, even the Earth’s fiery depths. All these interactions can mess with the salt levels.

What Really Controls Ocean Salinity?

So, if it’s not a simple case of rivers adding salt, what’s actually going on? Well, ocean salinity is a constantly shifting puzzle, with a bunch of factors all playing their part:

• Evaporation vs. Rain: This is a big one. When water evaporates, it leaves the salt behind, making the ocean saltier. On the other hand, rain adds fresh water, diluting the salt. That’s why you tend to find higher salt levels in places like the subtropics, where it’s hot and dry i. And lower salinity near the equator, where it rains a lot i.
• Freshwater Floods: Rivers and melting ice are like giant freshwater hoses, spraying into the ocean and lowering the salinity, especially near coastlines and the poles i.
• Ocean’s Conveyor Belt: Ocean currents are like rivers within the sea, moving water (and salt) around the globe. They can carry salty water from one place to another, changing the salinity patterns i.
• Temperature’s Role: Salinity, temperature, and density are all tangled up together. Warmer water tends to be saltier i. And salinity affects how dense the water is, which then influences how the ocean circulates i. It’s all connected!
• Weather Patterns: High-pressure zones with stable air and sunshine tend to have saltier water. And wind can push water around, piling it up in some areas and changing the saltiness i.
• Ice, Ice, Maybe Salty: When sea ice forms, it actually increases the salinity of the water around it. That’s because the salt gets squeezed out during the freezing process i.

A Salty Past: Not a Straight Line

Instead of a steady climb, ocean salinity has been all over the place throughout Earth’s history. During ice ages, when tons of water was locked up in glaciers, the ocean got saltier i. Then, when the ice melted, it got diluted i. Some studies even suggest that the ocean was much saltier way back when, especially before the dinosaurs roamed the Earth i.

The Verdict: A Big “Nope” for Salinity as Timekeeper

A good clock needs a clear starting point and a steady pace. Ocean salinity has neither. We don’t know what the ocean’s original saltiness was, and the factors that change salinity are constantly changing themselves i.

Early Guesses and Modern Science

Back in 1910, a scientist named George Becker took a shot at calculating the Earth’s age using ocean salinity. He came up with 50 to 70 million years. Turns out, he was off by a bit. Modern dating techniques have shown us that the Earth is actually around 4.54 billion years old.

The Bottom Line

Ocean salinity is a fascinating and complex property, shaped by a whole host of factors that shift and change over vast stretches of time. Because of this, it’s a pretty terrible way to measure the Earth’s age. While salinity is super important for understanding how the ocean works and how it affects our climate, it’s definitely not a simple “salt clock.” So, next time you’re at the beach, enjoy the salty water, but don’t try to use it to figure out how old the planet is!