Expert: Daniel Mazur - 10/26/2005

Question
Hi,

I'm an undergraduate stuck on a personal question, looking for more information in general on this topic. Any information you know of, especially of papers written on this topic would be wonderful.

I was wondering if a total nuclear war destroyed the earth as we know it, i.e. all human and animal life, would it be possible for the earth to "start again" in some evolutionary process? Would any gases or elements still remain? How likely is it that they would (eventually)transform  into intelligent life?

I have found some information on this, but it so far been unsatisfactory. I hope you can help.  I really appreciate your time on this!!! Thanks in advance,

Aaron.

Answer
Hi Aaron,

this is really an unusual question, but I'll try to think about it. I cannont recommend any papers or other resources on this subject as I have not read any of this sort. However, papers on related subjects are not that hard to come by. I'll come to that later.

Let me sum up and elaborate on your initial conditions: All human and animal life on Earth is Extinct due to a total nuclear war. This is a bit hard to imagine, because of all the bacteriae deep in the oceans and in the caverns. Should these be destroyed too, it would mean that the nuclear war produces enough heat to evaporate all oceans, melt down the complete Earth's crust and even heat up the whole atmosphere well above water boiling point and all this would have to last for long enough. Not just a total explosion, but a continuous state of immense hotness, so that all man-made satellites orbiting the Earth, all the bacteria in the dust in high parts of the atmosphere have time to fall down and be destroyed. This of course means destroying "all plants" too - you could not really think of a scenario when plants survive and animals don't, the two are too interdependent. At least no man-made weapon to date is able to do that. It is another question, whether mankind has or will ever have the destructive power to cause such total extinction, but I will not speculatee on that, for now I'll assume it is possible.

The meltdown described above then looks remarkably like the scentific image of the earliest billions of years of Earth's history - all surface melted, atmosphere full of water vapor and the tiniest organic molecules (methanol, simple aromates, molecules with high ratio of carbon). The only difference would be the high X-ray background from the decay of radioactive elements spread all over. Would it be possible for life to start over? My answer is: YES, IF THERE WILL BE ENOUGH TIME. And there should be, as I am going to explain now.

Life on Earth needs the Sun. Without the Sun, no life and no evolution is possible, let alone "intelligent" life. I do not like this expression; for me, a living entity is intelligent by definition (depending on our view "life" is a subset of "inteligence" or the two sets are identical, but you cannot have an entity fulfilling all conditions of "being alive" - metabolism, reproduction etc. - that has no intelligence. But this was a diversion, back to the subject. The current estimates of how long our Sun is going to live are around 10 billion years. Knowing that the radioactive materials dangerous to life all have decay half-times less than 10 000 years, we can disregard this point right away - even if you have to wait 1 million years for the radioactivity to die down, there is PLENTY of time!

So, after (say) 1 million years we come back to Earth (as insubstantial observers :-)) and we still see the same picture of molten surface, but with quite low background radioactivity, probably simmilar to what the Earth has nowadays when inhabitated by 6 billion human beings and countless other living entities. We will be then in approximately the same state Earth presumably was 2-4 billion years AGO! So, let's wait another 3 billion years and come back and the least we would see is a new Earth crust formed, new oceans, new atmosphere and it all will not be too different in composition (I mean the oxygen and nitrogen atmosphere, light-element minerals dissolved in water, deposits of heavier elements - metals - deeper in the crust...) from what it is now. The only thing missing (?) may be life.

We will be at time "minus 7 billion" years of Sun life, so there will still be several billions of years left before the Sun get's too hot and big. I should mention, there are predictions that the planet Jupiter is going to gain mass over time and eventually become a "small" star, effectively creating a double-star with Sun. This would most likely be fatal to Earth as well, but I do not know the time estimates for this to happen, so I'll disregard it now, as well as all other disasters (meteors,...) that could happen to Earth during those 3 billions of years of recovery. Simply, if all goes well, the conditions on Earth will then be very similar to what they were 1-2 billions years ago.

From here we can only speculate and our discussion will be more based on things we believe than on proven facts. Has life arrived to Earth in the interstellar dust? Has it developed in Earth oceans from the simple chemicals already available? Or has it all been a creation of an intelligent designer? We don't know and may never know. All a scientist can say is what I depicted to you: the Earth will return, in its inorganic part, to a state very much like the one now. The climate will be similar, Sun will be there, there will be lots of time available so there is no obvious reason for the life not to start again.

Supposing the unicellular life forms come up again, we can immediately assume that multicellular organisms will be formed too, in time. It will be life based on oxygen again, but question remains, if a molecule like DNA is going to exist in its today's form, or if there is going to be some other macromolecule to carry the hereditary information. In either case, a line of tests will be put in the way of life and there is little knowledge, if the life that exists now is "the most probable one" or if it had been "nudged" in one or more points of the evolution processby something extraordinary. Evidence that comes with the case of dinosaur extinction indicates that indeed these unexpected events can quite substantially influence the path of evolution. This, however, is more my belief than a rock-solid fact. I believe a meteor impact or a massive volcano explosion (or both) played a significant role in the dinos' eradication, but there are others, who believe that dinos' have just developed in a way that was insustainable and they died away simply because of lack of ready-to-eat prey. You see, it really is about people's beliefs.

To sum up, I think it likely that water-based life will develop again, but I don't think it will be too much alike the life that exists on Earth now. Evolution into "intelligent" life forms is possible, it would be prettymuch certain if the time given to it was infinite. However, several billions of years may or may not be enough... We don't know any other life than ours and therefore cannot tell, if our planet's evolution was fawst or slow or anything. It is similar to our position as individuals, if we are isolated from all other people - we cannot judge the normality of our life, if there is none other to compare it with.

Finally, let's get back to the articles you asked about. There is a lot of reading to be done about what readioactive elements are released in a nuclear war and then estimates, when the radiation gets back to normal. There is a lot of reading to be done about Earths early history, the cooling of the surface, creation of oceans and the various hypotheses about the origin of life on Earth. If you are a chemist, then water solution reaction mean times will be of particular interest. Then you can read on and on about the future of the Sun and the Solar system, about the probabilities of meteor impacts, and about essentially EVERYTHING that has something to do with evolution questions. You could just spend days and days with internet resources and in libraries, but be prepared that in the end, you are not going to come up with exact answers, you will have created a well founded opinion, though.

I hope this little essay works for you. Good luck with your research of this matter!

Daniel