The earth's worst mass extinction was:

late devonian
ordovician-silurian
permian-triassic
end triassic
cretaceous-tertiary

The Permian–Triassic (P–Tr) extinction event, colloquially known as the Great Dying, the End Jump up ^ St. Fleur, Nicholas (16 February 2017). "After Earth's Worst Mass Extinction, Life Rebounded Rapidly, Fossils Suggest". New York Times ...

Protons have a positive charge and, collectively, give an element its atomic number.