The hydrosphere is the water part of the Earth’s surface. 70% or more of Earth’s surface is actually covered in water. This includes ice at the polar caps, in glaciers, etc. There are 2 main types of bodies of liquid water: fresh water and salt water. The level of salt in salt water can vary considerably. Water can dissolve both solids and gas needed by life. Warm water dissolves solids better than cold, while cold water dissolves gasses better than warm. This is why there are often rich biological environments in cold waters. Most fresh water occurs as smaller inland bodies-like lakes and rivers. While it is the oceans that are salt water, fresh water can also be found underground in reservoirs or aquifers. A large percentage of the liquid water on Earth is in the oceans. When we look at Earth’s oceans we can divide them into the 3 main regions: Neretic Zone, Shallow Zone, and the Abyssal Zone. These zones are divided by water depth. Neretic Zone these are the shallowest regions of the oceans. This includes things like the shore lines, intertidal pools, etc. This makes up only a very small percentage. Shallow Zone: this is defined as the depth to which sunlight can penetrate or roughly 300. Within this zone photosynthesis is possible. Abyssal Zone: these are the depths to which light cannot penetrate. Life in these regions must depend either on organic material that sinks down, or on other energy sources than photosynthesis, generally this would be volcanic activity. Water has a high heat capacity. This means the oceans and other bodies of water can store large amounts of heat. This helps to regulate the temperature of the planet. Both the atmosphere and the hydrosphere are fluids, so they can flow. It is from this motion that we see the weather produced. The motions in the atmosphere and oceans result from 2 warm processes. These are convection and the coriolis force. Convection is the process whereby heat rises. In the atmosphere warm air can evaporate water and rise with it to higher altitudes. This produces clouds. In the oceans currents can arise as warm water rises or cold water sinks. The other force that helps produce both air and water currents is the coriolis force. This force is a result of Earth’s spin. This force causes the atmosphere to circulate in cells where the winds blow at high altitude in particular in constant directions. The air currents can carry either warm or cool air with them. There are also currents in the oceans that are either warm or cold. The combination of water and air and their movement produces weather. One important cycle that comes out of this interaction is what we call the hydrocycle. In this cycle water evaporates, is carried on the wind currents and is dropped elsewhere. This moves water around the globe, but the flow of water can also carry other materials that are necessary for life on Earth.
