Finding water could lead to finding life.
One element that all living things on Earth have in common is their need for water. Every living thing from the smallest virus to the largest elephant needs water to survive, wherever they live. Life on Earth is possible because of water. Astrobiologists,who are scientists searching for life on other planets, think that the key to finding life on other planets is the presence of water.
Earth’s water is mostly in the oceans.
The oceans, which cover 71% of Earth’s surface, contain 96.5% of all the water on Earth. Only 0.001% of all water is in the atmosphere and if all that water fell at the same time all over the world as rain, the whole planet would get about 1 inch of it.
Freshwater is frozen!
Freshwater is water with just a small amount of salts in it and only 3.5% of all the water on Earth is fresh. 68% of all freshwater is frozen in glaciers and ice, 30% is in groundwater and the rest in lakes, rivers and streams.
The concentration of salt in oceans is variable.
There is more or less 1 cup of salt ( sodium chloride – table salt!) in a gallon of ocean water, but the amount of salt in different oceans is not the same. The Atlantic ocean is saltier than the Pacific. On Earth the saltiest water can be found in Antarctica in a small lake called Don Juan Pond.
What goes on in a drop of water?
There is a lot of life in a single drop of ocean water. There could be millions of bacteria and viruses, fish eggs, little worms and baby polyps.
Comets may have brought water to Earth.
Originally there was some water within the rocky material that formed Earth, but probably not enough to fill all the oceans on our blue planet. It’s possible that comets, which are made from icy water, brought water when they fell on Earth. Maybe not all the water we see today has come from outer space in comets, but quite a lot could have.
What if ice sank?
Solid objects usually sink when put in water. This is because their atoms are very close together and so they are dense or very concentrated. When water becomes ice its molecules arrange themselves in rings with empty spaces in the middle. So ice is actually not as dense as water and so it floats! This fact is very important. If solid ice sank it would freeze the water around it. Floating ice lets the liquid stay liquid. Our oceans are not completely frozen mostly because ice floats.
Water makes up a large part of our bodies.
When a baby is born its body is 78% water, this proportion changes as we grow older and an adult’s body is made up of 55 to 60% water. Water plays an important part in our body’s functions. There’s a lot of water in our blood which brings nutrients to all the cells in our body, and takes away waste products. It also helps regulate our body temperature, think of sweat. In our brain and spinal cord it acts as a shock absorber. We really can’t do without it.
Water goes upwards in plants.
How come a drop of water is rounded and doesn’t flatten out? This is because water molecules tend to stick together and to other surfaces. This characteristic is typical of water and not many other liquids can do this. This fact explains how water can travel upwards from a plant’s roots to its leaves. Inside a plant there are thin tubes called xylem where water molecules move upwards by sticking to each other and to the walls of the tubes. The water vapor coming out of the leaves keeps the water flowing upwards.
The three states of water are easy to see, very uncommon!
We can see water in its three states all the time, in clouds as water vapor, its gas form, in rivers and lakes as liquid water and in ice and snow in its solid form. This is unusual because, while all other substances can be solid, liquid or gas, many of them change state only at very extreme temperatures. We don’t see liquid gold or solid oxygen because their melting and freezing points are at temperatures which would kill us.