Atmosphere of Earth However, polar stratospheric or nacreous clouds are occasionally seen in the lower part of this layer of the atmosphere where the air is coldest. The stratosphere is the highest layer that can be accessed by jet-powered aircraft. The troposphere is the lowest layer of Earth's atmosphere. It extends from Earth's surface to an average height of about , although this altitude varies from about at the geographic poles to at the Equator, with some variation due to weather. The troposphere is bounded above by the tropopause, a boundary marked in most places by a temperature inversion (i.e. a layer of
Opus: The Day We Found Earth their planet of origin to live among the stars. By then, Earth has become a mythical planet and the belief in its existence has become a religion called "Earthology". On the other hand, the human gene pool has deteriorated after millennia of genetic engineering, and the only way to revert this damage is to trace back to the oldest sample of genes left on their long forgotten home planet. Project Earth was then founded and a spaceship named OPUS was launched in order to search for Earth and save the failing human race. The story follows a childlike robot Emeth,