In Arthur C. Clarke's Talking of Space: Report on Planet Three, it seems that the author by comparing Earth and Mars not only shows its differences, but also provides foreshadowing into the possible future of the Earth—this tale of "warning" stresses the importance of "conserving life on our planet."
We find that the Martians cannot always see Earth as its occupants are on the side of the planet that is often turned away from Earth. This could symbolize an inability to "understand" life on this planet, especially as it might seem to a Martian that we have so many things that would benefit the Martian culture—and perhaps we are not appreciative enough of what we have.
To support the idea that the Earth is perhaps on a course to self-destruction, the moon is described as "silvery white" while the Earth is described as "sickly green." Had it been described as a lush green, we could assume that the color denotes health and growth. However, "sickly" brings to mind slime or rotting vegetation rather than healthy growth.
The benefits of Earth are presented in terms of what is lacking on Mars: there is no oxygen released by the Martians and therefore there is no ozone layer to protect the planet's surface; because there is no oxygen, there is no fire on Mars either, something so central to the civilization of mankind on Earth.
We wonder if perhaps life on Mars was once as it is now on Earth. The terrain on Mars does not have the mountains that made the spread of civilization on Earth so difficult at times. It is suggested that once Mars also had oceans filled with life, as does Earth. The atmosphere, which offers such abundant life on Earth, puzzles the Martian world.
Though the "author" notes that an "atomic nucleus" would assist Martian scientists in learning more about the Earth, the story has an apocalyptic ending, as the manuscript being read (we discover) has survived a "thermo-nuclear blast in Oasis City." Several things are inferred here: just as research in our world led scientists to believe that learning more about the atom and being able to "manipulate it" would bring knowledge and benefits, it has also brought the threat, and realization, of destruction in the form of atomic weapons. For the Martian society, it would seem (and this appears to be Clarke's warning) that when man cannot exercise good judgment with the scientific elements in the world (any world), life can be completely destroyed. While the Martians seemed to be an advanced life form, it would appear that atomic science destroyed them. Inference: the Earth must be careful and vigilant so our planet does not realize the fate of the Martians.
Clarke uses this "Martian" document to make several important points about the value of caring for our environment and the dangers that confront us if precautions are not taken.