The greatest threat?

Recently I was contemplating the significance of Earth Day (today, 22 April) and asked people on one of my websites what they thought of as the main candidates as the “greatest threat to Earth”. The answers included global warming (and related factors such as the ice caps melting and major coral reefs and forests dying), over-population, the lack of (or limited use of) renewable energy resources, a strike by a major asteroid or comet, some other major event in the Solar System, a nearby supernova and of course also the Sun.

My original question had been a bit misleading, because I wanted to see to what extent people equate the future of the planet with the future of life on Earth, and specifically the future of the human race. It is natural that we see the universe from the one point of view with which we can identify – the human perspective.

Although natural disasters may play a role, modern man is the probably the greatest threat to life on Earth - or to sustain life for beings such as the human race. There is no agreement on the time scales involved, but the majority view seems to be that, unless we act fast, we are heading towards destroying the environment to such an extent that in time to come, only very resilient life forms (and man might not be one of those!) will survive.


But Earth itself will still be here. Indeed even a catastrophic destruction of all or most species may not be the end of life on this planet – there have been mass extinctions before. Enough might remain of the conditions that once allowed life to start and thrive on this planet for it to start all over again. Would this evolve into intelligent life again? There is no way of knowing or predicting the answer to that question.

The statistics may be wrong and global warming may not lead to the end of life as we know it. However, life on Earth could theoretically also be destroyed at some future date as a result of a nearby supernova or powerful gamma rays resulting from some other cosmic event.

Yet the planet itself will be around until

• a large asteroid, comet or other body collides with it. However, it would have to be very large and hit the Earth at just the right angle and velocity to smash the whole planet apart. Even a Mars-sized object did not destroy Earth early in the history of the solar system, but rather lead to the formation of our beautiful and benevolent moon; or
• the dying Sun destroys it. It is thought the planet will become uninhabitable as the Sun starts getting hotter and brighter, causing a moist greenhouse effect. This will happen in a billion or more years from now. The Earth will lose its atmosphere and then its oceans will boil away and be lost into space – leaving the planet without liquid water. But only when the dying Sun reaches its red giant stage in roughly 5 billion years, it will expand to “gobble up” the inner planets, including possibly the Earth. When our star becomes a dense white dwarf at the centre of perhaps a spectacular planetary nebula, only the outer planets may remain to orbit around it.

Whether the expanding Sun will incinerate the Earth is uncertain – it depends on how large the red giant will be and the exact tidal interactions that take place at that time. A scorched little Earth may continue to orbit the white dwarf embers of the Sun.

Thus our life-giving Sun will also take life - and probably destroy our home planet - one day. It will form part of a large cosmic cycle that closes the loop to make all of what our planet is, was and will be, back into cosmic dust. Further into the future than the current age of the universe, the white dwarf sun itself will cool down to a point when it no longer emits heat or light and become a black dwarf. What follows (even black dwarfs are only theoretical objects since the universe is thought to be too young to contain any yet) is in the realms of theoretical physics and cosmology as the remaining object decays even further over trillions of years - time periods that become truly unimaginable.

It is perhaps sad to think of our planet as dying as a part of the normal cosmic cycle – but there is little sense in worrying about it too much because nothing man can do will prevent those events.�

Whether man - or something resembling the core of what man is today - will succeed somewhere in the future to leave this planet to continue some form of human existence elsewhere, will depend on an explosion of knowledge and technology that even modern man can hardly imagine today.

We could - and even should - start taking a long-term view because such technology will not materialise by some fluke. If we continue to be selfish and direct most of our research and human endeavours towards our own, relatively short-term needs of comfort, wealth and power (both in the energy sense and the political sense!), our species is doomed - whatever the fate of our planet.

We as mankind cannot conceivably destroy the planet as a whole - but we can destroy the environment in which we live. Ideally every day should become an Earth Day, with mankind acting responsibly towards our home planet and its fragile ecosystems.

Of course I may have it all wrong…