Planetary Milestone Reached: 66 Million-Year Event Mark Passed

In a quiet suburban home outside of New York City, writer Elizabeth Rayne shares her life with Lestat, her parrot. Known for her work in popular publications like Popular Mechanics, Ars Technica, and SYFY WIRE, Rayne's expertise extends beyond the written word. When not crafting compelling narratives, she can be found engaging in activities such as drawing, playing the piano, and, surprisingly, shapeshifting.

However, it's not just the world of fiction that's undergoing change. The real-world ocean, a vast and intricate ecosystem, is facing a crisis of its own. Sixty-six million years ago, an asteroid struck Earth, triggering the end-Cretaceous Mass Extinction, leading to the demise of more than half of all marine life. Today, a different kind of threat looms: anthropogenic activity, primarily deforestation and the burning of fossil fuels, has released enormous amounts of emissions, primarily in the form of carbon dioxide.

This carbon dioxide, when absorbed by the ocean, causes a significant drop in the concentration of calcium carbonate, a key component for many marine organisms, and a rise in ocean acidity. The planetary boundary for ocean acidification, as defined by scientists, is a 20% drop in the concentration of calcium carbonate from pre-industrialization levels. Unfortunately, recent research indicates that this boundary has already been crossed by as much as 60% of subsurface ocean waters located 200 meters below the surface.

This increase in acidity poses a significant threat to various marine life forms. For instance, pteropods, a type of zooplankton, form the base of an extensive food web. If disrupted, this could have catastrophic consequences. A separate NOAA experiment showed that some species of pteropods could soon find themselves unable to maintain the shells they need to survive, with their shells dissolving after only 45 days in water with carbonate levels adjusted to reflect projected carbonate levels for the year 2100.

Moreover, if deep-water corals are not able to build exoskeletons, entire ecosystems that depend on them for food and shelter could be wiped out. Creatures that make their own shells through calcification rely on calcium and carbonate molecules already floating around in the ocean. Too much carbon dioxide can throw off this process.

As rising temperatures heat up the ocean, warmer oceans hold less oxygen. This warmer water is more buoyant and does not mix as well with deeper, colder and more oxygenated water, leading to a deficit of oxygen known as hypoxia.

However, there's hope. The main advancement in assessing ocean acidification is shifting from an assessment based primarily on the changing chemistry to a more holistic approach that considers uncertainties, regional variations, subsurface impacts, and the biological consequences of exceeding the boundary.

Fortunately, no extinction-level asteroid is currently headed for Earth. But the threat of ocean acidification is very real, and it's up to us to take action before it's too late.