Supernovae and Life

Part 3 - Water

Oxygen and hydrogen combine readily with many other elements to form a variety of chemical compounds and together they form water, a compound vital for all forms of life. Water is known chemically as H2O. (The 2 means that two atoms of hydrogen combine with one atom of oxygen to make one molecule of water).

Water makes up about 60% of the human adult body;  about 73% of the brain and heart consists of water, and even the bones are 31% water.

Water has some unique properties. It freezes at 0°C and boils at 100°C at sea level. At an altitude of 10,000 feet (3048 m) water boils at 89.8°C.  It will also evaporate at lower temperature dependent on the amount of water already in the air.

As it evaporates from the liquid state (water) to the gaseous state (water vapour) it removes heat from the water (known as the latent heat of evaporation). Which is why the temperature of boiling water remains constant (at 100°C at sea level) until all of the water in a container has evaporated.

So, water evaporates easily into the atmosphere when it is hot and condenses out, as rain or snow, when the atmosphere cools. Thus it is carried in the air from the tropical oceans to the northern and southern extremities of Earth.

When air, saturated with water vapour, cools, it forms tiny water droplets that remain suspended in the air as clouds or (at ground level) fog. If the droplets coalesce they form rain or, if the temperature is below freezing they may link together in the complicated hexagonal crystals of snow flakes.

Water is also a very good solvent for a wide range of elements and compounds of elements. When rain water reaches land (or ice and snow melts) it begins to dissolve chemical compounds such as sodium chloride (common salt), calcium and iron oxide and carries these to the sea or to an area where the water again evaporates, depositing the dissolved compounds (minerals) in salt flats.

When sea water evaporates it leaves behind all chemical compound dissolved in the water. Which is why sea water becomes progressively more salty over time and rain or snow is almost pure water.

Water seeping into rock fissures and then freezing, expands, exerting enough pressure to split the rock. This is one of the processes that gradually reduces rock to sand and clay particles. Other processes that form soil include wave pounding on shorelines, water running over rocks and glaciers (rivers of ice) slowly grinding rocks together.

Unlike most other compounds, frozen water (ice) is less dense than liquid water and it floats on the surface of liquid water.

Snow on the ground contains a lot of air which makes it an excellent insulator. Snow on top of ice insulates like a blanket and prevents seas, lakes or rivers from freezing ever more deeply. Many animals survive frigid winters beneath the snow and every Canadian and Alaskan Inuk know how to make an iglu. (Snow house, igloo).

The sun has continuously emitted radiation with remarkable consistency, since it formed and this has kept the surface of Earth warm enough so that most of the water remained in a liquid state most of the time. Although there have been Ice Ages and periods when the planet was largely frozen.

As water can store more heat energy that any other material, so the oceans serve as a giant heat reservoir to moderate the climate near oceans. In some places inland and in desert areas, when there is no blanketing cloud cover, the air temperature can range below freezing at night to unbearably hot during the day.

Clouds also reflect radiation from the Sun back into space which keeps the Earth's surface cooler while, at night, cloud act as a blanket to prevent the surface heat from radiating into space.The atmosphere acts as giant heat transporter by carrying warm water vapour to cooler areas of the planet and returning cooler, drier air to tropical regions.

The oceans also transport heat from tropical regions to areas north and south of the equator with slow moving streams of warm water and under currents of cool water (carrying oxygen and nutrients) moving in the opposite direction. The most well known example is the Gulf Stream from the Caribbean area that keep Iceland and most of northern Europe much warmer than it would be otherwise.