How did the ocean form? 4 things to know about his past and present

Given how old the ocean is, it’s easy to think of it as a permanent fixture. But those salty waters had to come from somewhere, somewhere. How did we get this wide, bright eye of life?

The ocean has undergone many changes over the past few billion years, and is still evolving today. It plays a major role in climate regulation, including by balancing human-induced global warming. But this warming is also affecting the ocean, threatening life under the sea and beyond.

June 8 World Oceans Day celebrates the vitality and importance of the ocean and how we can do our part to protect it. Here are some facts you didn’t know about how the ocean is changing before our eyes and what its past can tell us about our present.

Our planet has not always had an ocean

The earth has been around for about 4.5 billion years, but for the first billion there was no ocean. This is partly because the planet is too hot for liquid water to form.

Eventually, the planet began to cool below the boiling point of water — 212 degrees Fahrenheit — which allowed the early ocean to form about 3.8 billion years ago, according to the National Oceanic and Atmospheric Administration. That’s when water began to condense in the atmosphere and rain in pools across the Earth’s landscape, said Peter Adams, a geologist at the University of Florida.

There is some debate about how water got to Earth. One theory is that volcanic activity expelled water vapor and other gases from the planet’s interior, where it existed long ago. Another hypothesis is that icy comets left water when they crashed into the early planet. As Adams points out, the truth may be a combination of these theories, as well as another involving the main collision event believed to have created the moon.

Regardless of the final explanation, Earth’s exact location in the solar system would be a perfect place for water to exist in all three phases — ice, liquid, and water vapor, Adams noted. If the planet were closer to the Sun, it would be too hot for liquid water to stick to it; if it were much farther away, there would be no water vapor.

“We’re in the Goldilocks zone because we can move water in all three forms of the planet, and because it can take all three forms, we’re in that sweet spot,” he said.

Ocean currents circulate around the planet, similar to the flow of our blood

Oceans make Earth habitable. That’s because it combines with the atmosphere to efficiently circulate heat and water around the planet, Adams said. Without ocean currents, the regions surrounding the equator would be much warmer, while those at higher latitudes would be much colder.

The Gulf Stream, a powerful current that brings warm water from the Gulf of Mexico to the east coast of North America and across the Atlantic Ocean to the British Isles, is a prime example of this phenomenon. This steady flow of warm water helps stabilize Europa’s climate, Adams says, which would otherwise be much colder and harsher at its latitude.

But currents and climate didn’t always work that way. Moving tectonic plates—fragmented pieces of the planet’s crust that constantly, slowly move over the mantle—have shaped and changed both land and sea over billions of years.

This map shows where the Gulf Stream originates in the Gulf of Mexico and how it travels northeast across the Atlantic Ocean to Northwest Europe.

This map shows where the Gulf Stream originates in the Gulf of Mexico and how it travels northeast across the Atlantic Ocean to Northwest Europe. Image courtesy of NOAA

“We’re really excited about the circulation and redistribution of heat in our oceans,” Adams said. “But if you reconfigure the tectonic plates, you’ll have different circulation patterns, as has happened and is happening throughout Earth’s history.”

Climate change also affects ocean circulation. As the planet warms, cold, fresh water frozen like glaciers melts and flows into the salty ocean, says Wesleyan University geologist Suzanne O’Connell. Because fresh water is less dense than salt water, it acts like a cap, blocking existing ocean currents, he said.

According to NOAA, disruptions in these currents could dramatically change temperatures in Europe and elsewhere.

“Think of the ocean as our blood. If you start to move your blood to another part, … [that’s] will have far-reaching consequences,” O’Connell said.

The ocean rises in some places and recedes in others

We cannot understand the deepest parts of the ocean or the highest mountains on land without tectonic plates, the 10-15 moving slices of the earth’s crust.

The ocean floor is expanding in some parts of the globe and shrinking in other parts. The continents of North America, South America, Europe and Africa were connected several hundred million years ago. Today, they sit on separate tectonic plates that share parts of the Atlantic Ocean.

Where these plates are located deep within that ocean is the Mid-Atlantic Ridge, an underwater mountain range that runs through the center of the Atlantic Ocean. At this point, magma pulses out of the underlying mantle and cools underwater to form new oceanic crust. According to the National Oceanic and Atmospheric Administration, it is spreading at a rate of two to five centimeters per year.

A world map shows the boundaries of each of the 15 to 20 tectonic plates, in addition to the contours of the continents.  They are color coded to show where one starts and the other starts.

The Earth’s crust is divided into moving tectonic plates that lie above its mantle. Image courtesy of the United States Geological Survey

You can think of the process as pulling the end of a piece of Play-Doh until a thin spot forms in the center, Adams said. But in this case, the tectonic plates are moving away from each other, allowing the ocean floor to expand.

“The new, low topography is right here [in the ocean]”, he explained. “And of course the water gets the low points because gravity moves it down. And you keep separating the Play-Doh, and you get a wider and wider ocean.

In contrast, the basin in which the Mediterranean Sea is located is shrinking and shrinking over time, Adams said. All of these changes are occurring on a time scale much longer than the human lifespan. The slow growth of the nail is almost imperceptible to a person, like the movement of a plate, he noted.

The ocean does so much for us, but we ask too much of it

The fossil fuels we burn to power our lives and societies release greenhouse gases that fill the atmosphere, causing the planet to rapidly heat up. This causes massive changes – much faster than on a geologic time scale like plate tectonics.

The planet’s temperature has fluctuated at other points in its long history, but those changes have generally been gradual, and organisms have evolved in response, O’Connell noted. But human-driven climate change is closer to more extreme events that leave little time for adaptation. In less than two centuries, he noted, “we have completely changed the atmosphere.”

Scientists can use ice cores from around 800,000 years ago to create a record of how much carbon dioxide was in the atmosphere during that time. For most of that time, CO2 measurements ranged from 180 to 300 parts per million. Today, those levels are about 420 parts per million, O’Connell said.


Researchers use ice cores to estimate atmospheric carbon dioxide levels over the past 800,000 years. Image courtesy of NASA

“If we’re going to warm the Earth and add all that CO2 over the next 20,000 years, it’s not a big deal,” O’Connell said. “But we’re not.”

The ocean helps mitigate some of the human-driven climate warming because water can absorb heat and much of it. But as it absorbs heat, it expands. The melting of the glaciers is also affected by a warming planet that collects excess water in the oceans.

“So as the Earth’s oceans warm, not only does the water in the oceans increase, but the water expands, increasing the height of the water column,” Adams said. Both of these processes contribute to sea level rise, which threatens coastal ecosystems and communities.

READ MORE: “The ocean has been forgiving” when it comes to absorbing carbon emissions. This may not last

Today, the ocean absorbs about a third of the carbon dioxide that humans emit into the atmosphere. This excess CO2 contributes to environmental changes such as ocean acidification, which affects marine animals with shells.

For O’Connell, it’s all a call to action. We cannot completely save ourselves or the ocean from climate change. But we have the power to quickly and meaningfully reduce greenhouse gas emissions and reduce the likelihood that researchers’ worst-case predictions will come true.

“We will rise to 1.5 degrees [of warming,] maybe even this decade. But the difference between 1.5 and 3 degrees is very big,” he said. “So, let’s not allow frost up to 2 degrees. Every part of the degree makes a difference.”

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