When and how will the Earth be destroyed?

One of the more morose facts I've carried in my brain since an early age is that the Earth is doomed to burn to a crisp in roughly 5 billion years (explained below). This thought creeps up in my mind occasionally when I think of the environmental movement and silly things it has spawned like "Earth First!" or the voluntary human extinction movement. What good is preserving the Earth when we know for an absolute logical certainty that the Earth will be completely destroyed by a date certain? Carpe diem, smoke 'em if you got 'em, use the Earth while we still can, I say. I'll let the reader run through the logical steps to that one, and may post on that particular topic later. For this post, I wanted to simply catalogue the various ways that the Earth can and/or will be destroyed (or all life on it destroyed) and put a time frame on each such potential or certain catastrophe.

I'll add links to this post later for reference but I wanted to get this down while I was in the mood (this is a post I've been planning on doing for a long time, and it will take a bit of googling to complete). What got me in the mood today was this article reporting that Stephen Hawking reports the (long-known) fact that the human race must venture into outer space in order to survive indefinitely. As the below will illustrate, well duh. The Earth will disintegrate, all life on it will be destroyed and we even know the outside dates. Hawking though stresses human-caused events like "sudden global warming, nuclear war, a genetically engineered virus or other dangers we have not yet thought of." (He may not attribute "global warming" to human causes, but given his list I doubt it. What about a non-genetically engineered virus? Or an extra-terrestrial "Andromeda strain”? Hawking's list is just a Lefty rant.)

This post is similar, but not identical to, this article about the top ten ways to destroy the Earth. Those top ten ways are mostly artificial, i.e., require the intervention of intelligent beings to bring about. Fundamentally, though, that list is made up of ways to destroy the Earth right now (or at least start the process right now) while my list is merely the various ways the Earth can or will be destroyed eventually by forces currently understood and in motion (and mostly outside our control).

So without further ado, here's my (incomplete for the moment) list of ways the Earth, and/or all life on it, will eventually be destroyed, listed in order of event most remote in time and indicating the probability the event will happen.

1. All energy in the universe running out - approximately a googol years (under current scientific understanding, certain to occur)

Within the past few years, scientists received a huge shock via observations of the speed and acceleration of the most distant galaxies. Ever since the change in thinking from the Einsteinian “static universe,” which he thought neither expanding nor contracting, caused by Edwin Hubble’s observations that the universe is expanding, the only question seriously considered was whether the mutual gravitational pull of all the matter in the universe was sufficient to re-collapse the entire universe or whether the expansion would go on forever, albeit at an ever decreasing rate. The most recent observations indicate that not only is the universe’s expansion not slowing down, it is speeding up!

We have no idea why the universe’s expansion is speeding up, but if it is, the fate of the universe is that all stars now formed, and hereafter to form, will eventually use all their useful nuclear fuel (which is anything lower on the periodic table than iron – above iron, no energy is generated from nuclear fusion). The universe will slowly freeze and, given its accelerating expansion, will never unfreeze. Black holes may form and eventually evaporate, mere atoms at a time, via Hawking radiation.

This is kind of a wild card in the list because the Earth will certainly be long gone before then (unless we find a way to move the Earth to a new star) but since it spells the eventual end of humanity and all other life in the universe, I figured it belonged on the list.

2. Swelling of the sun as its fuel runs out - 5 billion years (certain destruction of the Earth).

All stars of equal mass behave the same way, on the same timeframe. Stars shine because they have so much matter that the gravitational force is strong enough to cause nuclear fusion. The fusion reaction reduces the mass slightly and creates energy (E=MC²). The bigger the star, the quicker it burns its "fuel" and thus the quicker it self-destructs. The self-destruct sequence is different depending on the mass - at the high end, a black hole, then neutron star, then white dwarf, etc., result.

Our sun is destined to become a white dwarf. Before that, it will swell up to the size of at least the orbit of Mars, and the Earth, and all other inner planets, will gradually sink into the enlarged sun and burn to a crisp.

3. Collision with Andromeda galaxy – approximately 3 billion years (potential destabilization of Earth’s orbit with possible catastrophic consequences)

Even though the Universe as a whole is expanding, our nearest galactic neighbor, Andromeda, is moving toward us in the Milky Way. A “collision” with the Milky Way is possible, but not known for certain at this time. A collision would mostly mean the two galaxies “wisping” through each other with very few actual collisions of any sizeable objects. Assuming such a galactic collision occurs, it is highly unlikely that the Earth will actually hit anything in Andromeda. If anything in our solar system will get hit, it will likely be the sun.

In any event, many things could happen short of a direct collision of the Earth with another massive body if and when Andromeda and the Milky Way collide. The most likely is that the Earth’s orbit will be perturbed and eventually fall into, or away from, the sun. Either result would be fatal to all life on Earth. I’ll try to do the math later to determine how close a star from Andromeda will have to pass by our solar system to cause any significant perturbation in Earth’s orbit.

4. Collision with comet or asteroid – within 30 million years (near certain, though avoidable)

You’ve all seen the stupid movies and if you’re a geek like me you’ve seen the Discovery Channel shows. Yes, the Earth will likely be hit by another large stellar body like the one that wiped out the dinosaurs. When? The only large body we know of now that will come close to hitting the Earth will arrive around 2800 – 800 years from now. Our solar system is presently in a dense region of our galaxy such that the possibility of the Oort cloud being perturbed to send a comet on a collision course is more likely.

We have the technology to divert such a collision via rockets and nuclear explosions, provided we find the object in enough time. We have a better chance of spotting an offending asteroid (orbiting in the nearby Asteroid Belt between Mars and Jupiter) than a comet (plunging in from the Oort cloud beyond the Kuiper Belt). Depending on the size of the object, life on Earth may survive. The odds of humanity’s survival go up with more technological sophistication. But there is a size such that any object larger colliding with the Earth (calculated with respect to angle of impact and speed) will certainly destroy all life on Earth.

5. Gamma Ray burst from creation of a black hole – any time (highly improbable)

When a black hole forms, its poles shoot out super-massive amounts of gamma ray radiation in narrow cones. We see these gamma ray bursts occasionally, every one of which originated outside our galaxy (meaning that the energy has depleted such that it does us no harm). If a black hole forms near to us in our galaxy and its pole is aimed at us, the gamma ray burst will evaporate a significant portion of the ozone lawyer allowing the sun’s ultraviolet radiation to cause mass extinctions. The bigger the burst, the more ozone evaporated. With a large enough burst sustained for a more than about 30 seconds, the gamma rays would wipe out all the ozone, reach the Earth and fry everything on that side.

Humans could live through this at our present technological levels and the more advanced we get, the better our chances. Of course, our best chance is to establish colonies on other planets.

6. Eruption of the Yellowstone super-volcano – any time (near certain)

You, like almost everyone else in America, probably took a family trip to Yellowstone National Park, saw Old Faithful, saw the bubbling mud and steam vents, along with moose, bears, etc. Well, why do you think Yellowstone bubbles? It’s a super-volcano. It erupted in the past. It will erupt again.

There are other super-volcanoes. Any of them may erupt at any time. Modern volcanology allows us to predict eruptions of smaller volcanoes days and/or weeks in advance. Presumably, we would have more lead time with a super-volcano.

Again, humans could live through this, as such super-volcano eruptions have occurred during humanity’s existence, and we’re still here. A big enough eruption, though, would cause an ice age and would likely wipe out a significant portion of life on Earth and humanity.

That's all I have for you at the moment. I'm sure I'll think of more later. The above ought to keep y'all occupied for now.