Gamma Ray bursts are the brightest electromagnetic explosions known to occur in the universe. It is accompanied by intense radiation. A gamma ray burst striking on Earth would immediately increase the ultraviolet radiation. The long term effects of Gamma rays are not most dangerous ones. It can cause chemical reactions in atmosphere creating nitrogen oxide and nitrogen dioxide gas which will deplete the ozone, cause photochemical smog and cause nitric acid rain. It will ultimately lead to irreparable damage on Earth. 100 million years ago, moon was formed when a rouge planet Theia collided with Earth. Such a collision in future would certainly be the end of the humanity. A similar case was rumored to happen in future. Planet X (also known as Nibiru) was said to be on its way to collide with Earth.
However, NASA claims it’s just an internal hoax. This does not rule out that such a collision is possible in near future. Officially, the humanity has not yet observed any extraterrestrial intelligence (ETI), but contact with ETI remains possible. If any alien invasion occurs, then they can unleash an unfriendly artificial intelligence or performs a catastrophic physics experiment, or might choose to destroy humanity to protect other civilizations. Aliens may arrive on the Earth to attack, eat, or enslave humans, or they may simply carry unknown pathogens which can be fatal for the human race. The high carbon dioxide level in the Earth’s atmosphere is slowly lowering the pH balance of the world’s oceans and making them acidic. Once the ocean acidification is complete, the entire oceans will turn acidic, causing mass extinction. About 7–8 billion years from now, if and after the Sun has become a red giant, the Earth will be engulfed by the expanding Sun and destroyed. A billion years down the line, our sun will become hot enough to boil our oceans, making it inhabitable.
A few billion years from then, it will become a red giant engulfing everything in its way including the Earth. 66 million years ago, a 10 kilometer-wide asteroid struck the Earth surface. Upon the impact, it spelled a cataclysmic end of 75 percent of all life including dinosaurs. Asteroids still continue to hit the Earth. An asteroid of over 6.2 miles in size is capable of wiping off life from the Earth. The biggest threat is from the star, Gliese 710. It will come near the Earth in 1.3 million years. These asteroids will have the potential to cause a catastrophic impact on the Earth. Evolution is turning bacteria into super-bugs which have developed resistance to many traditional medicines. If they start mutating and evolving at a rapid rate, then the smallest of paper cuts would kill the healthiest individuals, creating a doomsday scenario. About 73,000 years ago, a 1,000-feet wave swept across the Earth.
In future, a mega tsunami of this magnitude can be the ultimate end for every organism on land including the human. As of 2016, there are 15,000 nuclear weapons on Earth. The statistics does not end here as every nuclear country is striving to modernize its nuclear arsenal. According to some experts, this increases the risk of nuclear proliferation, nuclear terrorism, and accidental nuclear war. While nuclear strikes could cause vast destruction in some regions, the main concern is its after effect. The nuclear winter after a nuclear war would change the climate. It would make the atmosphere extremely cold, threatening the existence of the whole humanity. Computers and machines are becoming increasingly sophisticated as advances in the field of artificial intelligence (AI) start to come through thick and fast. But some of the most intelligent people in the world are deeply concerned that one day in the not-so-distant future the robots could rise up against us, posing a threat to the very existence of humanity.