In modern life forms, energy occur in many variants, but basically two types: chemical energy and electrochemical energy. The latter is stored in cell membranes, while the former is the free energy in molecules that can react with other available molecules or break down to molecules with lower free energy. The earliest life forms used energy that was available, to a large extent due to reactions that had taken place at higher temperatures and which had frozen in the high temperature state. One of the high energy bonds that can be broken by addition of a water molecule is the phosphate bond. Two monophosphate molecules react spontaneously by heating to 160ºC. Two molecules unite to one molecule of pyrophosphates. Longer chains can also form by heating to higher temperatures, and different salts may also be formed. These are more soluble than the long phosphate bonds. These bonds are not broken by cooling. A catalyst is needed to break them. Early life forms used this energy to form RNA bonds. Thereby phosphate became the natural backbone of the RNA chains. As superheated water was many places poored out from the earth crust, pyrophosphates and other polyphosphates were available in ponds, lakes and oceans. No other energy source was initially needed, as these molecules were constantly resupplied. It has been hypothesized that a period of protein based evolution was needed before RNA could be created, but that is no problem at all. But other energy sources were also created. At the conditions that existed when the first forms of life appeared, also e.g. different sugars were formed, and they connected to the phosphate chains or monophoshates instead of ions, forming sugar phosphates. These were excellent as energy carriers, and we see them used e.g. in the glycolysis pathway.