Give a number in years. I'll give civilisation 70-80 at most with the final extinction event being a combination of the technological singularity and a grey goo situation. Possible causes of extinction of humanity: [b]Technological Singularity[/b] - Computational power exponentially increases and makes man obsolete. [b]Grey Goo:[/b] - Self-replicating robots, nano sized or otherwise are let loose and quickly consume the world with their superior intelligence. The world is consumed in 'grey goo'. [b]Global Warming[/b] - Anthropogenic climate change induces mass changes to the global ecosystem to a point where human practices such as agriculture are no longer sustainable, as well as an increasing frequency in extreme weather events [b]Global Pandemic [/b]- A global outbreak of an extremely potent bacteria/virus/fungus/parasite is extremely rapid in our globalised interconnected society and wipes out the worlds population. [b]Alien Invasion/Colonisation[/b] - A highly advanced Alien species that has travelled across the cosmos arrives in the Solar System and primitive humanity have no chance to defend themselves. (Think of what you do to ant mounds in your back garden.) [b]WR 104 Gamma Ray Burst[/b] (or any other high energy stellar emission) - Gamma Rays from space vaporise the Ozone Layer and other important elements of the atmosphere. [b]Asteroid Impact[/b] - An asteroid or large space body collides with Earth causing a high energy event on the surface that disrupts global food chains. [b]Supervolancoe[/b] - A massive volanic eruption occurs from a so called 'supervolanco' such as the one that is dormant under Yellowstone National Park. The huge amounts of ash circulate around the globe and the atmosphere becomes opaque to the UV and visible light that warm the planet. The global ecosystem literally freezes. [b]Nuclear Armageddon[/b] - A nuclear confrontation between two nations leads to massive nuclear fallout that wrecks global systems both natural and anthropogenic and leads to a breakdown of society. [b]Solar System Disruption[/b]- A large body appears in the Solar System from interstellar space disrupting the orbits of bodies on a minor scale at first, but these compound to fling much larger bodies out of their orbit with the sun. [b]Sun Runs out of Fuel [/b]- In billions of years time the sun begins to run out of fuel and swells until the Earth is consumed in the firey ball. [b]The Big Crunch[/b] - The Universes momentum from the Big Bang no longer can hold it from re-collapsing down into a dense state in accordance with Newton's Law of Universal Gravitation. Unlikely due to the discovery of dark energy and not in our lifetime. [b]The Big Freeze [/b]- The Universe continues to expand due to the increasing force of Dark Energy (due to the stretching of space itself) the the until all stars burnt out and entropy reaches a maximum state. Heat is lost and life cannot survive. Not for trillions of years. [b]The Big Rip[/b] - An alternative to the the Big Freeze, the repulsive force that permeates all space, actually turns out to increase in potency per unit volume and eventually all stars are flung out from the galaxy. All planets are flung out from stars. All bound objects including atoms and nucleons are torn apart over a period of eons. Not for trillions of years.