Earth, Water, Air, and Fire: The Four States of Matter

The ancient Greeks believed that there were four elements that everything was made up of: earth, water, air, and fire. This theory was suggested around 450 BC, and it was later supported and added to by Aristotle. (Aristotle also suggested that there was a fifth element,aether, because it seemed strange that the stars would be made out of earthly elements. He would be surprised to learn that they are in fact made up of many elements found on earth, and are so hot they could be said to be on fire all the time!)  

The idea that these four elements - earth, water, air, and fire - made up all matter was the cornerstone of philosophy, science, and medicine for two thousand years. The elements were "pure" but could not be found in that state on earth. Every visible thing was made up of some combination of earth, water, air, and fire. The four elements were even used to described the four temperaments a person could have, and Hippocrates used the four elements to describe the four "humors" found in the body. These theories stated that the temperaments and humors needed to be in balance with each other in order for a person to be well both mentally and physically. While we do know now that these previous theories are false, in a way the four elements do align with the four states of matter that modern science has agreed on: solid(earth), liquid (water), gas (air), and plasma (fire).  

Although the Greeks believed that the four elements were unchanging in nature, everything was made up of different elements, which were held together or pushed apart by forces of attraction and repulsion, causing substances to appear to change. This is similar to what really happens with elements and all molecules at an atomic level.

Matter is anything that has mass and volume and is made up of atoms, which are the smallest particles of matter. Bonding occurs among atoms to make larger molecules. (Click here to learn more about bonding.) Mass is how much matter is in an object whereas volume is how much space the object takes up. How atoms are arranged in an object determines whether it is a solid, liquid, gas, or plasma.

• In a solid, the atoms are packed closely together in an ordered pattern and cannot move, giving a solid a definite volume and shape. Examples of solids include rocks, wood, metal, and ice.

• In a liquid, the atoms are close together but can move around each other. This allows a liquid to take the shape of whatever container it is placed in. Examples of liquids include room temperature water, room temperature mercury, and hot lava (molten rock).

• In a gas, there is more space between atoms. The atoms can move so freely that if the gas is not trapped in a container, the atoms will diffuse and spread throughout the atmosphere. Examples of gases are oxygen and nitrogen (in the air we breathe), helium, and steam (water vapor).

• In a plasma, the atoms are spaced similarly to gas except there is so much energy in a plasma, the atoms actually split into smaller pieces. Plasmas are able to carry an electrical current and generate magnetic fields. Examples of plasmas include lightning, solar wind, the sun, fluorescent lights, and neon signs.

Temperature plays an important role in how the atoms are aligned in a substance. As a general rule of thumb, the colder the matter is, the closer the atoms are to each other, and the warmer the matter is, the farther the atoms are apart. Of course, the temperature at which a matter is a solid or a liquid depends on what substance the matter is made of. For example, water at room temperature is a liquid whereas a rock at room temperature is solid.

Earth, Water, Air, and Fire: Active Role in Everyday Life

The earth is full of a wide variety of rocks and minerals which provides the soil to grow vegetation and support life. The two most common elements in the earth's crust are oxygen (46%) and silicon (28%). Because of this, the most abundant mineral in the earth's crust is silica (silicon dioxide). More commonly known as sand, silica is a major component of glass. How can glass be made out of sand? Interestingly, when silica is heated, it melts and becomes glass, hardening as it cools.

Rich deposits of metal ores are found throughout the earth's crust. While these metals are used in the production of machinery, tools, buildings, and weapons, straight out of the earth these metals are pretty useless. Fire is used to heat, refine, and shape metal so that machines, hammers, and support beams can be made from it.

It is easy to think of the earth as being solid dirt through and through, but in reality it is made up of several layers. While many of these layers are solid, the layer that surrounds the core is called the liquid outer core. It is so hot inside the earth that the rock at this layer has actually melted. The solid inner core is just as hot as the liquid layer surrounding it, but the pressure on the inner core is so great that scientists believe it is "pressed" into a solid.

The chemical formula of water is H20, meaning it is made of two hydrogen atoms bonded to one oxygen atom. The hydrogen atoms each attach to one side of the oxygen atom and have a positive charge whereas the oxygen atom has a negative charge. This polarizes the water molecule, much like a magnet, giving a water molecule positive and negative ends. Since opposite charges attract, water molecules tend to "stick" together. This gives water surface tension and allows objects, such as paperclips, to float on it.

While it can't dissolve everything, water is known as the universal solvent because it can dissolve more substances than any other liquid. It can dissolve salt, sugar, acids, alkalis, some gases, and organic material. Water traveling through your body or through the ground takes chemicals, minerals, and nutrients with it. Water's ability to dissolve substances helps keep the planet healthy. For more than a century, the burning of fossil fuels has pumped large amounts of carbon dioxide (CO2) into the atmosphere. The water in oceans have absorbed about half of this CO2 by dissolving the gas from the air and processing it by sea vegetation.

Water has a high specific heat index, meaning that it takes a lot of energy to change its temperature. This is essential for life to survive on a planet. The abundance of water on the earth keeps the planet in a very short but comfortable temperature range. The average surface temperature of the earth is 59 ° F with the highest recorded temperature 135.9 ° F and the lowest recorded temperature -128.6 ° F. To compare, it would seem logical that Mercury, the closest planet to the sun, would stay really warm on all surfaces of the planet, regardless if it was facing the sun or not. However, while the surface facing the sun does reach very warm temperatures (up to 800 ° F), the surfacing facing away from the sun drops to a chilly -280 ° F. Mercury's lack of water is responsible for this drastic temperature change because the dry material that makes up its surface cannot hold heat like water does. To experience for yourself how well water does keep temperature from drastic fluctuations, pay attention to the change between daytime and nighttime temperatures the next time you visit a maritime (near the ocean) or desert climate. You'll probably notice there is little to no temperature change near the ocean, whereas in the desert there is a significant change in daytime and nighttime temperatures.

This high specific heat index also helps water put out fire by cooling the fuel surfaces that the fire is burning, removing the heat needed for the fire to burn. Water also smothers a fire by preventing it from getting the oxygen it needs to burn.

Air was considered a "pure" element, but in fact the air that's all around us is made up of a variety of gases: primarily nitrogen and oxygen, with almost 1% argon and even smaller amounts of carbon dioxide and other elements such as krypton and helium. The composition of air is just right for life on Earth, though. We use a lot of the oxygen we get from the air, then breathe out carbon dioxide - which plants need to manufacture their food through photosynthesis. Plants in turn give off oxygen during photosynthesis.

Although air is invisible (and most of the time we forget it is even there), it does take up space, it has volume, and it exerts pressure. This can be seen when you take an "empty" glass, turn it upside down, and try to push it down to the bottom of a sink full of water. If the glass was truly empty, the water would easily fill the inside of the glass. But air is in there, and only a small amount of water can enter the glass. The air in the glass was compressed, giving the water some space that was previously occupied with air. It is a good thing that air fills empty space because air all around us actually presses down on us all the time. We would collapse under the weight of the air, except air is also inside us and exerts pressure that balances out the pressure exerted by the outside air.

How does fire work? It's closely linked to air. Fire needs three things in order to exist: oxygen, fuel, and heat. The intensity of a fire varies because it is dependent on the oxygen, fuel, and heat available to it. When all three of these things are in a controlled situation, such as in candles or a campfire, fires are considered helpful. But when one or more of these things are not controlled, such as in a wildfire or a burning building, fires can easily become very dangerous. To extinguish a fire, the oxygen, fuel, or heat needs to be removed. "Smothering" a fire by placing a blanket or dirt on it works because the fire goes out without oxygen. The earth provides an abundance of fuel in the form of wood and fossil fuels such as coal. When the fuel is removed, the fire has nothing left to burn and is extinguished. Water often serves as an effective cooling source by removing the heat from a fire. This is seen when hot lava from an erupting volcano enters the ocean or when a bucket of water is dumped on a campfire.

Fire creates light, heat, and smoke by a rapid chemical reaction called combustion. Smoke is the result of the incomplete combustion (burning) of a fuel. Particles that were not burned become suspended in the air. Smoke is often dangerous because it contains harmful gases that can poison a person who inhales too much smoke.

You might be surprised to know that our bodies also use "combustion" to produce energy from oxygen and food through metabolic processes. We need a steady supply of oxygen to keep our bodies functioning normally; if there's too little oxygen in the air, we'll suffocate. At the same time, we can be thankful there's not more oxygen in the air, or the chemical reactions in our bodies would speed up, causing us to soon "crash and burn"! Too much oxygen in the air would also increase the risk of fires on the earth. Since nitrogen and argon are not very reactive, air is pretty safe for us.