What happens when everyone dies?

Answer 1

This would depend on how exactly everyone died. The "best case" scenario would involve a selective virus that would wipe out all human life while having no effect on any animal species. At this point, we would become an abundant food source for the animals of the world. This feast would be a jump-start to the re-emergence of abundant animal and plant species across the globe. Trees would grow where now there is grass, and eventually forests would grow in the suburbs. Species that are now endangered would return to prevalence as they would no longer be hunted by man, and the size of the habitat would grow by five thousand percent in many cases. Roads would slowly crack and become subsumed into the ground.

If nuclear warfare were to kill everyone, most larger animal species would also be eradicated, as they are far too sensitive to radiation poisoning to survive nuclear war. However, many species are extremely resistant to being killed by nuclear radiation, including cockroaches and rats. Nuclear winter would greatly reduce the amount of animals living for a time, but eventually it would clear and plant and animals life would slowly repopulate the planet. Life would continue, but it would be radically changed.

If a meteor were to hit the planet and cause a "nuclear winter," we would likely see a similar scenario to nuclear war, with a massive die-off followed by a slow re-population.

This can also happen over a period of time due to climate change, ozone depletion, heat and cold phenomenon and man's interference in his uncontrolled destruction of nature, complete exhaustion of all forms of energy and other hundreds of catastrophes brought upon the world by human beings.

Answer 2

There are at least a couple of billion years left in the lifespan of our own sun, and many, many times that remaining for other systems (some not even born yet).

Eventually, however, as the Universe ages, it crawls inexorable toward its ultimate demise. Long after the last sun goes cold, the entire universe may reach a point called 'heat death' - where it achieves maximum entropy. Insufficient energy will remain to support life or motion, and all the universe will be of equal temperature.

It is one theory.