Ocean — Reading Comprehension Lesson

Reading Passage

Ocean

The world’s oceans cover about 71 percent of Earth’s surface and contain about 97 percent of all the water on the planet. The ocean is divided into five named basins — the Pacific, Atlantic, Indian, Southern, and Arctic oceans — though they are all connected into one continuous body of water. The Pacific Ocean alone is larger than all of Earth’s landmasses combined. The average depth of the ocean is about 12,100 feet, with the deepest point, the Mariana Trench in the Pacific, reaching nearly 36,000 feet.

Scientists divide the ocean into vertical zones based on how much sunlight reaches them. The sunlight zone, or epipelagic zone, extends from the surface to about 660 feet deep. Here, enough light penetrates for photosynthesis to occur, making this the most productive zone. Most ocean life, including fish, sea turtles, dolphins, and sharks, lives in or depends on this zone. Below it lies the twilight zone, where dim light filters down but photosynthesis is not possible. Deeper zones — the midnight zone, abyssal zone, and hadal zone — are completely dark, cold, and under enormous pressure.

Ocean currents are like rivers flowing within the ocean. Surface currents are driven primarily by wind and distribute heat around the planet, moderating climates on nearby landmasses. The Gulf Stream, for example, carries warm tropical water northward along the eastern coast of North America and across to Europe, keeping European cities warmer than other locations at the same latitude. Deep-water currents move much more slowly and are driven by differences in water temperature and salinity.

The ocean plays a critical role in regulating Earth’s climate by absorbing heat and carbon dioxide from the atmosphere. Oceans have absorbed more than 90 percent of the excess heat produced by human greenhouse gas emissions since 1970. However, this comes at a cost: warmer water causes coral bleaching, disrupts marine food chains, and raises sea levels. Ocean acidification — caused by the ocean absorbing carbon dioxide, which forms carbonic acid — threatens shellfish, corals, and other organisms that build calcium carbonate structures.

Printable Worksheet

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