Hydrologic Cycle

What percentage of Earth’s water is in the World Ocean?

98.9% of Earth’s water is in the World Ocean.

What percentage of Earth’s water is in the atmosphere?

~0.001% of Earth’s water is in the atmosphere.

How much of Earth’s water is in lakes and rivers?

~0.007% of Earth’s water is in lakes and rivers.

What percentage of Earth’s water is underground?

~0.035% of Earth’s water is underground

What percentage of Earth’s water is stored as ice?

~1.6% of Earth’s water is in ice on the continents.

How much of ocean water evaporates each year?

1/37,000 of ocean water evaporates annually.

What happens to most of the water that evaporates from the ocean?

89% returns directly to the ocean as precipitation.

What percentage of evaporated ocean water falls as precipitation on land?

About 11% of evaporated ocean water falls as rain or snow on land.

How does water return to the ocean from land?

Through runoff, rivers, streams, melting glaciers, and groundwater flow.

How does oceanic crust differ from continental crust?

Oceanic crust is denser (3.0 g/cm³) and thinner (7 km) than continental crust (2.7 g/cm³, 40 km thick).

How old is oceanic crust compared to continental crust?

Oceanic crust is no older than 200 million years, whereas continental crust can be up to 3.8 billion years old.

 What percentage of Earth’s surface is below sea level?

71% of Earth’s surface is below sea level.

What is the mean depth of the ocean?

The mean depth of the ocean is 3,800 meters (2.36 miles).

What is bathymetry?

Bathymetry is the study of the topography of the sea floor.

What are common topographic features of the sea floor?

Rugged mountains, steep canyons, active volcanoes, and deep trenches.

What are the four major features of ocean margins?

1. Continental Shelf – Gently sloping, extends to ~200 m depth.

2. Shelf Break – Abrupt slope change marking the edge of continental crust.

3. Continental Slope – Steep slope from shelf to ocean basin floor.

4. Continental Rise – Thick wedge of sediments at the base of the slope.

What are the four key features of the deep-sea floor?

1. Abyssal Plains – Very flat regions covered by thick sediment.

2. Abyssal Hills & Seamounts – Often extinct volcanoes rising from the sea floor.

3. Mid-Ocean Ridges & Rises – Volcanic subsea mountain ranges marking crustal plate separation.

4. Trenches – Deep depressions where oceanic crust is subducted into the mantle.

 Why is the hydrologic cycle important to oceanography?

It regulates Earth's climate and ensures the continuous movement of water between the ocean, atmosphere, and land.