The ways our world could end tomorrow

These are the most likely scenarios that could happen

1>A proxy war between the world powers escalates into a full blown nuclear war . Neither side is willing to back down. The war doesn't stop until near total annihilation of both sides. Regardless of whether a nuclear bomb is dropped on your country or not, the nuclear fall out of  a war on such a scale, will affect the entire world. All future generations would be born with genetic defects. This could lead to the eventual loss of intelligence and the dying out of the entire human species. The whole process could take less than a few hundred years.

2>If a flu virus with the survival instinct of HIV emerges, such that it keeps the host healthy and oblivious long enough to be able to transmit but not too long, it is just a matter of few years that most humans get wiped out. How ever such a scenario may not lead to the total destruction of humans. There are un contacted tribes of people (Sentinelese people for example). Due to their isolation from mainland humans, they might survive such an event. (It is possible that the existing humans today survived such an event 70,000 years ago)

3>Eruption of the super volcano in yellowstone national park.  This super volcano which spans the area of the whole yellow stone national park, has a history of erupting every 600,000 years or so. The last one was around 640,000 years ago. According to the scientists the next eruption is already overdue. This could even be tomorrow! If this happens, most of North America would be wiped out. The resulting ash and debris released into the air by this unimaginably gigantic volcano, would block out the sun for the entire planet. This would lead to destruction of harvest and a global cooling of about 10 degree Celsius. Mankind would survive but the world wouldn't the same anymore.

Have we been visited by Aliens?

Based on archaeological findings, we have an idea on the history of evolution. We know about the Dinosaurs and the creatures that came and left before and after them. But what seems interesting is that every dominant creature rules for a few million years and then gets wiped out to make way for the next. This leads me to two questions
1> Is the whole earth an alien experimental ground?
2> Are we next?

 Life on earth developed into complex forms about 3.5 Billion years after its formation. So keeping in mind that the universe is 14 Billion years old, it is possible that intelligent life forms developed else where in the universe about 3.5 Billion years after it formation, which is about 10 Billion years ago. Even if a handful of these survived (looking at the enormous size of the universe, it is very probable) beyond wars and asteroids, they would be 10 Billion years ahead of us in technology! My tiny brain can't even begin to imagine what that technology would be like. What I feel is that, earth was visited by Aliens at around 4 Billion years ago and then started this experiment, where the visiting aliens released these DNA programmed creatures into the earth and saw how it played out. And time to time, they do a reset by wiping out the dominant species for the next stage of the experiment to begin. Like the robots we build are not aware of our presence, similarly is it possible that the creatures on earth are not intelligent enough to recognize this higher power? Or is it that humans had an inkling of this higher power which led to the misguided creation of the religions? Maybe the aliens are not even physical beings. Its probably an existence that influences our physical world but has no physical form that we understand.

Some  random facts that support my theory

• Our only purpose in life seems to be the replication of our DNA and the traits that were introduced in us over history due to the influence of our DNA (If you think about it, the creatures, the various cultures, none of it would had existed, had it not been for the existence of DNA). 
• Human ancestors were like any other animal. Then around 100,000 years ago  the creature that was barely distinguishable from the other animals, started increasing its intelligence at an exponential pace. Fast forward into the present, we fly to space and land on the moon.  A change like that in 100,000 years is instantaneous in relation to the 3.8 Billion years of the evolution of life. It seems plausible that an external catalyst could have been present.