calcium

noun

1. (countable, uncountable)The chemical element with atomic number 20: a soft, silvery-white alkaline earth metal which occurs naturally as carbonate in limestone and as silicate in many rocks.

   “Oxygen levels on Earth skyrocketed 2.4 billion years ago, when cyanobacteria evolved photosynthesis:[…]. The evolutionary precursor of photosynthesis is still under debate, and a new study sheds light. The critical component of the photosynthetic system is the “water-oxidizing complex”, made up of manganese atoms and a calcium atom.”

   ““This material has a specific hardness and is chemically very stable. It forms naturally from calcium alone, but bacteria accelerate the transformation into calcium carbonate,” explains Alejandro Montesinos, head of the Decarbonization, Climate Change, and Circular Economy Research Group at Tec de Monterrey and a member of the Institute of Advanced Materials and Sustainable Manufacturing.”

2. (countable)An atom of this element.