to build the proteins we need to survive. All organisms need some proteins, whether they are used in muscles or as simple structures in the cell membrane. Proteins perform a vast array of functions within organisms, including DNA replication, responding to stimuli, and transporting molecules from one location to another. To make DNA and RNA, the carriers of the genetic code for life on Earth, nitrogen is needed.


9.3.4 Phosphorus


Phosphorus is formed mainly in stars which are more than about eight solar masses. When such massive stars end their lives as supernova explosions, current models suggest that phosphorus is made either during a stage just prior to the explosion, or in layers during the explosion itself. It may also be made in stars greater than about 15 solar masses by neon and carbon fusion. In the universe as a whole, phosphorus is a relatively rare


element, with an abundance level of only seven parts per million, but in the Earth’s crust this rises to 1,000 parts per million. Te question of how and why Earth became so phosphorus-rich has puzzled astronomers and geologists for decades. Perhaps a phosphorus-rich asteroid or comet could have formed and later hit the Earth? However, without such a large impact event to inundate the Earth with phosphorus, advanced life would have remained impossible. A lack of phosphorus on Earth would have favoured phosphorus- impoverished life-forms such as simple bacteria. Like carbon and nitrogen, phosphorus thus is key to


terrestrial life: phosphorus and phosphates are components of the double-helix backbone of DNA and the energy transport molecule ATP, which transports chemical energy around the body’s cells, powering nearly every cellular process that requires energy. Phosphorus works with calcium to help build bones and it makes up 1% of our body weight.


Figure 9.42: Cassiopeia A is a supernova remnant in the constellation Cassiopeia named after Queen Cassiopeia in Greek mythology, the wife of Cepheus, King of Aethiopia, and mother of Princess Andromeda. Queen Cassiopeia was placed in the sky as a punishment for her boast about her and her daughter’s unrivalled beauty. This beautiful supernova lies about eleven light-years away within the Milky Way and was made in an explosive event in the year 1681. In 2013, astronomers detected phosphorus in Cassiopeia A, which confirmed that this element is produced in supernovae.


Figure 9.41: DNA, short for deoxyribonucleic acid, is believed to have evolved from basic proteins in the warm oceans of primeval Earth. DNA is a complex molecular structure that is coiled into every cell in your body. The cell gets its instruction on what do to from the DNA. You may think of the cell as being the computer while DNA is the computer program. Within each string of DNA are sets of instructions called genes. A gene tells a cell how to make a specific protein which is used by the cell to perform certain functions, to grow, to reproduce, and to survive. About 99.9 % of the DNA of every person is exactly the same. It is the small 0.1% that is different which makes us all unique. No one knows if DNA-like molecules will also define life that originates outside of Earth.


9.3.5 Sulphur


Sulphur is the tenth most abundant element in the universe. It is part of most biochemical processes on Earth, and most enzymes cannot function without it. It is also a component of many vitamins and hormones. Te average adult human body contains 140 grams of sulphur and takes in about one gram a day.


Figure 9.43: A solfatara – a fumarole that is emitting sulphurous gases – in Vulcano, Italy, a small volcanic island in the Tyrrhenian Sea, about 25 km north of Sicily. Often seen in the neighbourhood of volcanoes, a fumarole is an opening in the Earth’s crust which emits steam and gases such as carbon dioxide, sulphur dioxide, hydrochloric acid, and hydrogen sulphide.


323


NASA/JPL-Caltech


Wikimedia/Zephyris


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