40,000 years. It's an unfathomable number when you really stop
   and thing about it. Imagine going backwards in time rather
   quickly. It's 2015. Now it's the 1950s. Now it's the 1880s.
   1840s 1700s. Your time device speeds up. it's 1110 AD, 500 AD 29
   AD 250 BC
   Get ready to say good bye to Ancient Greece. 2500 BC 5000 BC
   You're in Egypt and China and Indonesia Now... 40000 BC
   Indonesia. You're in a cave. You're bored. So, you decide to
   paint something to pass the time... and figure out how to get it
   on Facebook in 42015 years' time.
   http://www.smithsonianmag.com/science-nature/rockart-ages-indonesian-cave-paintings-are-40000-years-old-180952970/?utm_source=smithsoniantopic&no-ist