‘The ocean is like a giant soup’: Seawater today still contains traces of Earth’s ancient past

BINGHAMTON, N.Y. — Researchers have discovered drops of seawater containing traces of an ancient world. A team of scientists from Binghamton University found that sea salt carries with it tiny droplets of the original seawater, effectively capturing snippets of Earth’s geological past.

Their findings revealed valuable insights into ancient geological processes and climate variations.

“The ocean is like a giant soup of different elements,” says Tim Lowenstein, Binghamton University’s Distinguished Professor of Earth Sciences, in a university release. “Sodium and chloride are the most common ones, but there are dozens of others dissolved in seawater in trace amounts such as lithium.”

Their research spanned sea salt (known as halite) samples, which had formed over epochs spanning the past 150 million years. These samples, extracted from sedimentary basins across continents from the United States to Africa, carried within them pockets of this primordial seawater.

Harnessing the precision of lasers, researchers drilled into these salt crystals to extract the ancient droplets. Subsequent analysis with a mass spectrometer shed light on the concentration of specific trace elements like lithium. Over the 150-million-year time span, there was a seven-fold dip in lithium concentration. Simultaneously, there was an uptick in the magnesium-to-calcium ratios.

This puzzle of seawater composition has been a point of contention for researchers for over 20 years. Researchers proposed a theory: the lithium drop can be attributed to the dwindling production of the oceanic crust coupled with a decline in seafloor hydrothermal activities. Both these phenomena are directly impacted by the movement of tectonic plates.

Waves at beach, ocean
Photo by Matt Paul Catalano on Unsplash

A slowdown in tectonic plate activity led to less lithium being released into the ocean. This, in turn, meant reduced carbon dioxide emissions into the atmosphere, culminating in the global cooling and our current ice age. To put things into perspective, rewind 150 million years, and Earth was a warmer haven with heightened levels of atmospheric carbon dioxide and more lithium in its oceans.

“There is a close link between ocean chemistry and atmospheric chemistry,” says Dr. Mebrahtu Weldeghebriel, a postdoctoral fellow at Princeton University. “Whatever changes happen in the ocean also reflect what’s happening in the atmosphere.”

The findings underscore how tectonic plate movements have dictated the composition of Earth’s waters and the atmosphere over millennia. This, in turn, has ramifications for marine biology, influencing creatures that form shells using calcium carbonate.

“The oceans and atmosphere are connected to one another, and how they change is related,” notes Lowenstein. “Everything is connected.”

The study is published in the journal Science Advances.

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