The arrival of flying saucers raises important points:
Visitors to the planet would first by visual observation or object proximity detection, find a debris field surrounding the planet. Derelict space craft, bits of metal, discarded tools bags, nuclear and toxic chemical materials etc.
Next they would observe a brown pall of pollution in the atmosphere over east Asia. Then smoke drifting over the planet. Either from deliberately set fires, used to drive out wild animals for hunting or capture. Or blazes in forests caused by micro and macro mismanagement of the ecological systems in question.
Scanning of the planet would reveal toxic and nuclear material in both the oceans and on land. Life sign analysis would determine the most numerous large species had reached numbers the rapidly diminishing and degraded ecological systems could no longer support.
Independent objective planetary assessment systems aboard the craft would show that in terms of intergalactic and cosmic time scales the planet was in the final seconds of it’s death throes.
The benevolent visitors might decide to administer the cosmic equivalent of a blow to the back of the head with a spade to a myoamatosed rabbit. Just to spare us further suffering before our imminent deaths.