The word "species" is a noun. Here is an example of its usage in a sentence:
There are over 28,000 species of fish on the planet.
The word 'toad' is a noun, a word for a species of amphibian; a word for a thing.
"Earth" is a thing, and "things" are nouns. "Earth", then, is a noun.
part of speech
The part of speech for this particular word is a noun.
The part of speech for "answer" is a noun.
adverb
what part of speech is beneath
The part of speech for "explicit" is an adjective.
The part of speech for "twirl" is a verb.
The part of speech for "unfamiliar" is an adjective.
The part of speech of "came" is a verb.
The part of speech for "lecturer" is a noun.