How does the lava cooling to form rock set
the potassium-40/argon-40 clock to zero?

In “Ozymandias,” Percy Shelley explores the theme of the futility of power and might, and contrasts it with the immortality of art. He uses three narrators to tell the events of the poem. The poem is a frame story. The reader first encounters the main narrator. Shelley begins the poem by talking about how the narrator met the traveler:

I met a traveler from an antique land,

Who said—"Two vast and trunkless legs of stone”

At this point, the narrative shifts to the second speaker, the traveler. The traveler’s main function within the poem is to give us, the readers, the setting. He describes the desolate landscape in which he saw the ruins of a once-glorious empire. Through him, Shelley prepares us for the emotional impact of Ozymandias’s final words. It is through him that we get a description of Ozymandias’s power and pride:

Half sunk a shattered visage lies, whose frown,

And wrinkled lip, and sneer of cold command,

Through the traveler's description, we realize that while Ozymandias's power, symbolized by the ruins of his statue, has faded, the art of the unknown sculptor who captures his expression survives:

Tell that its sculptor well those passions read

Which yet survive, stamped on these lifeless things,

The narrative voice shifts once again, and we hear Ozymandias’s words:

My name is Ozymandias, king of kings:

Look on my Works, ye Mighty, and despair!

After one has read the traveler’s description of the ruins, Ozymandias’s words come across as pathetic and ironic, which is Shelley’s intention. He uses the word despair in Ozymandias’s boasting to his enemies. However the same despair could now be used to describe Ozymandias’s degraded state. At the climax of the poem, we recognize the irony of the fact that the once-great ruler Ozymandias is now unknown, and we get the only information we have of him from a stranger. So, by using narrative shifts, Percy Shelley increases the final emotional impact of the poem.