Silicon is the second most abundant element in the Earth's crust and is the seventh most abundant element in the Universe, after hydrogen, helium, oxygen, carbon, nitrogen, and magnesium. However, silicon is not the second most abundant element in the biosphere. The most abundant elements in living organisms are hydrogen, oxygen, carbon, and nitrogen, followed by calcium and phosphorus. Silicon is not essential for most organisms and is not found in high concentrations in living tissue.