Like Christmas lists, science-lists can be consulted for data. Like those in everyday life, they can become more interesting if they can be interpreted. So let’s make sense of the lists of elemental abundances in the universe, in Earth and in our bodies.
The overall composition of our planet is related to its proximity to our star. Like Mercury, Venus and Mars, Earth has a solid surface—unlike the gaseous envelope of more distant planets. Within, the terrestrial planets have a mostly iron metallic core surrounded by a silicate mantle. Of the most abundant elements making up the entire planet Earth, of those that could be parts of metal and rock, we find in order of abundance: iron, oxygen, silicon, magnesium, nickel, calcium and aluminum. In a non-identical but similar order, these, understandably, are also all present in a list of the universe’s most common elements. (see further down)
Those in top of the list were all (and still are) produced from simpler elements by large stars and supernovas. The latter also disseminate the material that their explosions or precursor stars produced, while their shockwaves help preexisting material condense into planets. But at least in the Earth’s crust, the elements of rocks and metals are bonded into compounds. More often than not, the metals and silicon have long ago reacted with oxygen, while sulfur is a distant second choice.
Why? Loose holders of electrons such as metals and metalloids react with nonmetals. The most common nonmetals, and also the most common nuclei in the universe are hydrogen and helium, both primordial and the simplest. Helium, like neon, is an inert member of the least reactive family of the periodic table. Hydrogen, even more abundant than helium, unfortunately forms hydrides, which are not the most stable of metal compounds. For example, they react with water to regenerate hydrogen gas. When hydrogen is incorporated into minerals, most often, it’s piggybacking in the form of hydroxide with the 3rd most abundant in the universe: oxygen. Its most common isotope, 16O has a doubly “magic” number of 8 protons and 8 neutrons. It is formed in stars from the fusion of helium and carbon. Moreover, oxygen partners not only with hydrogen in becoming part of minerals, but, independently of hydrogen. Oxygen readily binds to iron, aluminum, silicon and others. The compounds yielded—silicates, oxides and hydroxides— are far more stable than hydrides. This is the reason why it’s the 2nd most abundant element on Earth.
Although hydrogen is a component of water, the universe’s most abundant element is conspicuously absent from the Earth’s top-element list. It makes us realize that even though Earth’s surface is 70% water and its atmosphere, 5% water vapour, both are thin layers compared to the planet as a whole. Isotopic abundances strongly suggest that our planet’s water was an inadvertent gift from the heavens, landing here during a period when asteroids frequently crashed on our surface. Our solar system, however, even in its infancy, was not the birthplace of water. Elemental hydrogen and oxygen, in all likelihood, reacted to produce life’s key compound billions of years earlier in molecular clouds.
Life depends on water, which is an excellent solvent with a high vapour pressure and high specific heat. Although relatively stable, H2O can also be dissociated into both protons and an oxidizing agent, properties crucial to photosynthesizers. So it’s not a shock to see oxygen and hydrogen as the first and third most common elements in the human body and in most life forms. In between is the universe’s fourth most common atom, carbon. Carbon, unlike its cousin silicon, can catenate with itself. Like silicon, it can incorporate common elements like oxygen and also hydrogen, nitrogen and sulfur. This allows it to make a variety of large molecules with a wide range of chemical and physical properties. In addition, it can make simple molecules like methane and carbon dioxide. The pair is a source of carbon for anaerobic organisms, and the latter is the source for plants and algae.
High on the human list are phosphorus and potassium. Like all odd-atomic numbered elements other than primordial hydrogen and nitrogen(made in a stars’ CNO cycle), P and K are much rarer in the universe. An odd number of protons or neutrons destabilizes the nucleus. But potassium ions in animals are needed for the transmission of nerve impulses, and it also depolarizes hair cells, which allows us to hear. For organisms without ears or muscles— like plants— potassium ions are still essential in that they help stomata(plant pores) open and close to allow for the exchange of essential gases.
Meanwhile phosphorus is needed by all life for crucial ions and molecules. One is ATP, which puts a good leaving-group on reactants and lowers energy barriers in our biochemistry. It’s also part of the genetic molecules RNA and DNA. Phosphorus’ paucity on Earth has been a constant challenge while our population mushroomed, tripling from 1700 to 1910 and then tripling again in the next 77 years. While the growth has slowed down in the past generation, food consumption per capita has increased. Whereas, once upon a time, livestock and bird waste supplied farming with enough phosphorus, our food supply now relies on phosphate rock (mostly from China, Morocco and the United States) as the primary source of the essential element.
Sources:
Oxygen Origins https://www.nature.com/articles/nchem.1226
On The Cosmic Origins Of Carbon And Nitrogen https://arxiv.org/abs/astro-ph/0004299
Water was Plentiful In the Early Universe https://phys.org/news/2015-05-plentiful-early-universe.html#:~:text=New%20research%20poised%20for%20publication,universe%20was%20only%205%20percent
Top 10 Phosphate Countries By Production https://www.investingnews.com/amp/top-phosphate-countries-by-production-2655242583
Vangioni-Flam, Elisabeth; Cassé, Michel (2012). Spite, Monique (ed.). Galaxy Evolution: Connecting the Distant Universe with the Local Fossil Record. Springer Science & Business Media. pp. 77–86. ISBN 978-9401142137.
Trimble, Virginia (1996). “The Origin and Evolution of the Chemical Elements”. In Malkan, Matthew A.; Zuckerman, Ben (eds.). The origin and evolution of the universe. Sudbury, Mass.: Jones and Bartlett Publishers. p. 101. ISBN 0-7637-0030-4.
Croswell, Ken (February 1996). Alchemy of the Heavens. ISBN 0-385-47214-5.
Sciences in the Mural of Life 
