As a species we tend to look at ourselves as all-powerful, that our existence is guaranteed as the dominant species on the planet. The reality is that we are fragile people and it wouldn't take much to wipe us completely off the face of the earth. That being said, you shouldn't be too worried about the world ending tomorrow, but these five situations are the most likely to bring an end to life as we know it.

1. Nuclear War

During the 1950s the world saw the real threat that nuclear holocaust could wreak on the world. Russian and the U.S. had nukes pointed at each other with their fingers hovering over the launch triggers.

It seems like we are going to get closer to another potential nuclear standoff between the U.S. and North Korea. If one launches a nuke at the other, you can bet dollars to doughnuts that the other will retaliate. A nuclear war between only two of the world's nuclear states would kill hundreds of millions of people.

It isn't the initial blasts and heat waves that we have to worry about, it is the nuclear winter that would follow a full scale nuclear attack. It would destroy our ability to grow crops for years, even decades. Starvation and disease would set in, and humankind would be pushed to the brink of extinction.

2. Bio-engineered Pandemics

Natural-born pandemics have killed more people throughout history than every war's body count, ever. Think smallpox, Ebola, the plagues of medieval Europe, tuberculosis, malaria, and the list goes on. These are all naturally occurring and they have struck throughout history with deadly efficiency. Now imagine if a pandemic was engineered in a lab...

We can now take these diseases and make them deadlier by making small changes to their genetic makeups. Mouspox was altered during an experiment and it proved that you could infect people who had been previously vaccinated against it.

The chances of some group, or someone with a grudge making a batch of a super-pandemic are low. But as technology advances and things become cheaper and more readily available, the chances will continue to grow.    

3. Artificial Intelligence

Being the most intelligent species on the planet has definitely had its advantages for humans. We don't have preternatural strength or agility. We dont posses massive claws or razor sharp teeth. If you really look at it, we are kind of soft, jelly-filled sacks that most of the animal kingdom could tear to shreds, if we weren't intelligent.

Software-based, self-aware artificial intelligence might take a long time to develop, but if it ever were to become a reality, it could potentially surpass human intelligence faster than we can imagine. Think about that, machines and robots with higher levels of intelligence than us, made of far tougher material, and with no concerns for emotions.

Now a machine uprising is likely not coming down the pipe anytime soon, but several major figures in the scientific community (Stephen Hawking and Elon Musk to name a couple) are expressing major concerns towards AI and what it could mean for us.

4. Nanotechnology

Imagine being able to control weapons on a molecular level. Think about firing a bullet and knowing it was designed with a specific purpose on the molecular stage to do more damage than it normally would. That isn't likely to happen, bullets are already pretty good at randomly killing people, but imagine taking that concept and applying it a specially designed poison...

Being able to control things on an atomic or molecular level would allow you to design weapons with a very specific mandate, and it's terrifying. Think the original G.I. Joe.

5. The Unknown

A couple of decades ago, the idea of there being anything else out there in universe was laughable. But what we have come to understand is that the universe is far larger than we could even comprehend. It doesn't seem likely that in a universe of billions of stars and planets that we are alone.

Is there a chance that one day we may be visited by another race of intelligent beings (likely far more intelligent than us)? If they exist and mean us harm, there is likely nothing we can do about it.

Which scenario worries you the most?