Earth's Oceans online Quiz

Although the ocean covers over 70% of the Earth's surface, scientists estimate that only about 15% to 20% of all species live in the ocean. The vast majority of Earth's species live on land, largely driven by the immense diversity of terrestrial insects.

Despite modern advancements, less than 20 percent of the ocean floor has been mapped with high-resolution sonar technology. The remainder is mapped primarily using satellite altimetry, which provides much lower resolution.

Approximately 97 percent of Earth's water is saline and stored in the oceans. The remaining 3 percent is freshwater, mostly locked up in glaciers, ice caps, and underground aquifers.

Historically and oceanographically, the global ocean is divided into four principal basins: the Pacific, Atlantic, Indian, and Arctic Oceans. The Southern Ocean is also recognized by many modern organizations, but the classic four principal areas exclude it.

The ocean covers approximately 71 percent of the Earth's surface, leaving about 29 percent as land. This is why Earth is often referred to as the 'blue planet'.