In the poem "Earth," the speaker imagines what might happen should the Earth one day collide with the Sun. He wonders if a child looking up on a distant planet might see the destruction of the Earth and exclaim, "See the pretty shooting star!" The fact that the destruction of the Earth, and with it all of human history and civilization, might be to a child on a distant planet nothing more momentous than a brief, curious spectacle, suggests that life itself, as we know it, is indeed fragile. It also suggests that life as we know it is, at least from a different perspective, insignificant and meaningless.
This idea that human life is insignificant and meaningless is also emphasized throughout the poem when the speaker categorizes all of the life forms on the Earth as "the little crawling things." In this category the speaker places "ants, philosophers, and lice" and also "cattle, cockroaches, and kings." The implication here is that when life on this planet comes to an end, the kings shall be no more significant than the cockroaches and the philosophers no more important than the ants. Human life is thus insignificant and meaningless because it is short-lived and because whatever it builds will not last.
Throughout the poem the speaker describes the Earth and the humans who live upon it as "little." In the opening line, he calls the Earth "this little world," and later in the poem he classifies humans as "little crawling things." The repetition of the word "little" helps to emphasize the idea in the poem that life as we know it is insignificant. This impression is also emphasized by referring to humans simply as "things," no better than "lice" or "maggots."