Summer beach trips mean warm temperatures, bright sunshine and sandy beaches. And after months of winter’s frigid temperatures and snow, even the ocean’s not-so-good tasting salt water has its appeal. These beach vacations made us wonder: why is the ocean salty? Today, we answer this question with help from the United States Geological Survey (USGS).

Did you know about 97 percent of all water on and in Earth is saline? According to USGS, “if the salt in the ocean could be removed and spread evenly over the Earth's land surface, it would form a layer more than 500 feet thick, about the height of a 40-story office building.”

But how did this salt get in the ocean?

It happens in three ways: surface runoff, hydrothermal vents and submarine volcanism.

Among other elements, our atmosphere contains a small amount of carbon dioxide gas. When it rains, some of that gas dissolves into the water droplets, which causes rainwater to be slightly acidic. When the rain hits Earth, the acids break down the rocks’ salts and minerals and carries them to streams and rivers in a dissolved state of ions. This movement of rainwater is called runoff. If the dissolved ions are not used by the ocean’s organisms, they remain in the water and their concentrations increase over time.

More recently, scientists discovered that hydrothermal vents also contribute to the ocean’s mineral makeup. Hydrothermal vents are openings in the planet's surface where geothermally heated water exits. This hot water issued into the ocean contains large amounts of dissolved minerals from the rock on the oceanic crust.

Finally, similar to the hydrothermal vents, when underwater volcanoes erupt, the seawater reacts with hot rock dissolving some of the minerals and spouting them into the ocean’s waters.

According to USGS, the two ions that make up over 90% of all dissolved ions in seawater are sodium and chloride. Do you know what else is made up of sodium and chloride? Your table salt.