Easy. Answer is oxygen because it says which one was missing before any life was on earth. And in order to have life on earth you need oxygen!
:)
Explanation:
Determining a substance's physical or chemical identity. What are the two main requirements for identification? The adoption of testing procedures that give characteristic results for specific standard materials and the number and type of tests needed to identify a substance to exclude all other substances.
It is a wels catfish also called sheatfish it also looks like a catfish
Answer:
Invertebrates have a very quick life cycle and die very easily, as a result, they evolve very quickly into many different types of animals. also, they are often very small and their ecosystems are subject to much quicker change than that of vertebrates, meaning that mutations in their genes become relevant more often. Many invertebrates span very large areas (sea animals span most of the oceans, insects span entire continents) and so they evolve to be different species in different places.
Or
They do not have bones, they live on water or land, they can have soft bodies or exoskeletons, and others are parasites.
