Everyone Must Have Heard Of 2012. Actually, December 21-23 2012 A.K.A Doomsday. Well, Scientist Believe One Of Which Will Happen:

The Increase Rotation Of The Earth's Core, Thus Splitting The Tectonic Plates, Resulting In Massive Eruptions Of Supervolcanoes.
The Great Increase In Number Of Sun Spots On The Sun, Thus Shotting Massive Radiation Directly On The Earth, Resulting In An Inhabitable Planet With Much Radiation.
Planet X, Collides With Earth. Measured Theoretically, At The Point Of Impact, It Will Create An Explosion The Size Of Approximately 2.3 million Hydrogen Bombs.

Simply Put It, Humans Will Cease To Exist If Any Of Those Happen. But Will It? What If It Happens Earlier? What If It Happens Later? What If Nothing Ever Happens? I Believe In Whoever's Up There, And Believe That He Will Decide When We Will Leave This Planet. But What I Don't Believe Is Suddenly Disappearing In Thin Air And Leaving This World(That's What My Friend Say Though).

Sadly, All Of Them Are Theories. And Can Be Only Proven When The Time Comes, And By That Time, It Will Be To Late To Tell Them ' I Told You This Would Happen'. But If It Doesn't, I Will Have The Temptation To Tell Them ' I Told You So'. It's Never To Late Say That. But Like I Said, I Might Happen Later. Who Know's What The Heavens Has Prepared For Us. Just And See. Hopefully, Try Not To Do Anything Stupid Before You Die, Unless You Are Confirmed Of Your Appending Death.

But Hey, We Well Never Know It That Time Comes, Until Then, Live A Great Life.

Maya Civilization Just Had To Make This Sort Of Calender.