71% of the world is already covered with water. If the rest of the Earth were covered with water, then the entire planet surface would become one massive saltwater ocean and virtually every species that lives on land or in freshwater(e.g., streams, rivers, and lakes) would go extinct (die).

Humans and a huge diversity of other species, including most plants, birds, mammals, reptiles,amphibians, and insects, depend upon the exposed land surfaces to survive. These land surfaces provide us and other terrestrial species with food in the form of edible plants and animals; with habitat and shelter from the elements so that we can rest, hide from predators, and reproduce; and more importantly,these land surfaces provides us with sources of freshwater that we can drink.

Some people and some animals that live on land survive on food sources that originate from the ocean. For instance, many people fish in the sea for food or cultivate algae and shellfish in the oceans. Also, some birds and other land animals regularly eat organisms that wash up onto the beach. However, even if we were to feed entirely on fish and other marine foods, we would still need fresh drinking water to survive.

If the entire world were covered with water, then the only source of freshwater would be rain and other forms of precipitation (e.g., snow, hail, etc.). So perhaps some humans could survive by drinking rainwater and feeding entirely on marine foods. Since some terrestrial species do not require freshwater to drink because they get all the water they need from the food they eat, it is possible that a few terrestrial species might survive if the world were covered with water, provided they could adapt quickly to the flooding of their land habitats. Most likely, these would be species that already live in close association with the ocean, feed from the ocean, and can reproduce near or in the ocean, and so are not strictly terrestrial but rather a mix between terrestrial and marine.

If the world were covered with water, many of the ecosystems near land would also probably suffer, such as coral reefs, kelp forests, mangroves, and salt marshes. These ecosystems require plenty of light and need to be located in shallow areas close to the water surface. When the sea level rises, these ecosystems need to continually move towards land and shallower areas in order to keep up with the rate of sea level rise and stay in the well-lit zone just below the surface.

If the sea level rose at a rate faster than these ecosystems can move, they would be starved of light and end up dying as well.

Right now the sea level is rising due to global warming. Since the Earth is warming on average due to the greenhouse effect (increasing carbon dioxide in the atmosphere traps heat that is emitted from the Earth and radiates that heat back to the planet rather than allowing it to escape into space), the oceans are also absorbing more heat and are warming as well. When the water in the oceans warms, it expands and the sea level rises. The melting of glaciers on land (in places like Antarctica, Greenland, and Alaska) and the run-off of this melt water into the oceans is also contributing to rising sea levels.

Contrary to popular belief, the melting of the polar ice caps (ice floating on water in the Arctic Ocean and Antarctic Seas) is not contributing directly to any raises in sea level. This is because the volume of water that the ice in the polar ice caps occupies is equal to the volume of water created when this ice melts so that there is no change in the water volume due to melting. In other words, if you place an ice cube in a glass of water and measure the volume of water in that glass, and then let the ice cube melt and re-measure the volume of water in the glass, the volume of water will not have risen (in fact, the water volume may have decreased slightly because the water is colder after the ice melted than before it melted and cold water contracts).

However, polar ice floating on the oceans helps keep glaciers and ice sheets on land cool and hold them in place. The melting of ocean ice in Greenland and Antarctica is thought to increase the rate of glaciers melting on the land behind them and raise the sea level.

Well, it would certainly change our lives a lot. Given enough time people could probably figure out how to survive - grow food, obtain fresh water, build shelter, etc. but since we currently depend so much on the land, a sudden biblical flood type event would be a disaster. The recent flooding in New Orleans is an example of how devastating a sudden deluge can be.

What a creative question! If the world were covered with water, land plants and animals (like us) would not be able to survive.

One problem is that the water would probably be salty like seawater. Most of the plants and animals you are familiar with need a source of fresh water in order to survive. Land plants need soil, light, and just the right amount of fresh water to live.

Too much water kills some plants. Land animals like humans, monkeys, and bears need dry land and fresh water. Of course, some plants and animals thrive in seawater, and so they would be very happy living in bigger oceans.