Oceans make up about 71% of the earth’s surface. They’re important to the health of the earth and human beings. However, up to now, just 5% of the ocean has been explored and less than 10% has been mapped using modern technology. If we can send satellites（卫星）millions of miles into space, then why has so little of the ocean been studied?
One reason is that the ocean is not as simple as it seems to be. We’ve always been able to study the ocean’s surface. But we’ve only just started looking into the deep ocean within the past thirty years. Satellites have helped us study the ocean’s surface. If we want to dig deeper, more advanced（高级）technology is needed. But when we reach the deep ocean about 200 meters or more below the ocean’s surface, we will enter complete darkness. At these great depths, it’s very dark and cold and the pressure is deadly.
As you can see, deep sea exploration is difficult. But there is still hope to learn more. Many organizations arc making efforts in ocean exploration. “Scientists arc supported to study unknown and little-known areas”, a spokesman from one organization said. It’s hard to protect our ocean if we know so little about it. And there are many reasons why we should protect it. The main reason is that the ocean produces more than half of the world’s oxygen（氧气）.
【小题1】How much of the ocean has been mapped up to now?【小题2】Are humans looking into the deep ocean nowadays?
【小题3】What is the ocean like at the great depths?
【小题4】Who are supported to study unknown and little-known areas?
【小题5】Why should we protect the ocean according to the passage?
