Earth’s oceans may have been more acidic earlier in our planet’s history, as life was beginning to form and evolve. And that information not only tells us something about the beginning of life here but also about how climate change will affect our future.

“The acid-base balance of the oceans has been critical in maintaining Earth's habitability and allowing the emergence of early life,” according to a study in the journal Science, so researchers analyzed the cycles of seawater to better understand what the oceans looked like in the distant past.

Read: Fossils Found by Accident Show Evolution of Earth’s Early Marine Life

They say the pH level of the ocean — a measure of its acidity or alkalinity that goes between 0 and 14 — a few billion years ago was in the neighborhood of 6.5 and 7.

Urine, saliva and milk all have slightly acidic pH values of 6. On the scale, 7 is a neutral number, the middle ground between acids and bases where pure water lies. Blood is also a 7. And today’s current ocean waters are typically an 8.

The scientists, from the Weizmann Institute of Science and Stanford University, explained that the acidic ocean gradually turned to a saltier one in part as the Sun got brighter and the amount of carbon dioxide in the air was reduced.

That relationship between the content of the ocean and carbon dioxide in the atmosphere is “an important process for understanding the effects of climate change,” according to a statement from the Weizmann Institute. “Rising CO2 levels are currently increasing the oceans’ acidity.”

But even though early life on Earth thrived in slightly acidic oceans, that happened as the pH level was being maintained over millions of years and only gradually changed.

“Today’s acidification from CO2 is much more rapid,” the Weizmann Institute’s Itay Halevy said in the statement. “Hundreds of thousands of years from now, the oceans will have found a new balance, but between now and then, marine organisms and environments may suffer.”

See also:

Prehistoric Climate Change Caused 3 Mass Extinctions in a Row

Volcanic Rock Holds Evidence of Young Earth