### Was That It?

Last One To Leave, Turn Out The Lights.

This was originally written for a science-writing competition on the now-defunct Richard Dawkins forum. I've presented it here with only a bit of formatting and tidying, but otherwise exactly as presented originally. The original date of publication was 19 February 2010.

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How will the human species end? What will it look like?

Of late, there has been a good deal of focus on various stories concerning the end of the human species, and the 'destruction' of the planet. I want here to look at a couple of them, and then to look at what the science says about realistic scenarios with regard to the end of the human species.

It's a subject that has fascinated humans for as long as we have had stories. What will the ultimate fate of the species be?

The obvious place to begin, then, is some of the myths that seems to be on everybody's lips at the moment: 2012

Maya, 2012

According to some, the Mayan calendar ends on December 21st 2012, and this has been taken as a prophecy that this is when the world will end. Fortunately for us (he says with tongue firmly in cheek), this idea is not supported by any archaeological evidence at all. The date is a significant date in Mayan mythology, however, according to Maya expert and archaeoastronomer Anthony Aveni, of Colgate University, New York.

The Maya's relationship with time was on a scale almost unmatched until the advent of General Relativity. While other cultures the world over have constructed monuments that show a deep understanding of the passage of time, such as the neolithic monuments of Northern Europe, whose entrance passages are lit by the sunrise on specific days of the year, few cultures have so completely revolved around time as the Maya.

During the empire's heyday, the Maya invented what is called 'The Long Count', a circular calendar that began at what the Maya saw as the beginning of the last creation period on August 11th 3114 BCE, effectively fixing the beginning of their culture to that day, which they called 'day zero'. The 'Grand Cycle' that December 21, 2012 represents the end of is said to last for 1,872,000 days, or 5,125.37 years. At this point, the cycle ends and another cycle begins.[1]

Nibiru, 2012

There has, for some time, been a story circulating that a mysterious 'Planet X' is headed for Earth on a collision course. This planet, named Nibiru (probably from a term in Akkadian for 'crossing', but also appearing in ancient Babylonian astronomy as the highest point of the ecliptic, or Summer solstice) is allegedly going to hit Earth, or at least pass close enough to cause massive devastation, either by tidal means or by dragging bolides in its wake which will impact Earth.

This story seems to have its roots in work by Zecharia Sitchin, author of several books promoting 'theories' of human origins involving 'ancient astronauts'. According to Sitchin, Nibiru was the home of the Nephilim described in Genesis (he believes that they were also the Annunaki of ancient Sumerian myth). Nibiru allegedly collided with Tiamat, another planet supposed to lie between the orbits of Mars and Jupiter, creating Earth, the asteroid belt, and the comets. [2]

Sitchin believes that Homo sapiens were genetically engineered by the Nephilim by crossing extraterrestrial genes with Homo erectus.

Needless to say, no such planet has ever been discovered. David Morrison, of NASA's 'Ask an Astrobiologist' project, has this to say:

You don’t need to take my word for it. Just use common sense. Have you seen Nibiru? In 2008 many websites said it would be visible to the naked eye in spring 2009. If a large planet or brown dwarf were headed for the inner solar system in 2012, it would already be tracked by hundreds of thousands of astronomers, professional and amateur, all over the world. Do you know any amateur astronomers who are watching it? Have you seen any photos or discussion of it in the big popular astronomy magazines like Sky & Telescope? Just think about it. No one could hide Nibiru if it existed. [3]

 V838 Mon, which has been passed off as evidence for Nibiru.
Of course, those of us who pay attention to reality know that it's a star with an expanding gas shell, and 20,000 light-years away.[4]

Polar Shift Scenario

This is a little myth that has been gathering some steam of late, and one that has also been connected to 2012 in some of the stories that have cropped up. First properly proposed by electrician Hugh Auchincloss Brown in 1948 (although there were earlier proponents in one form or another), it was claimed that polar accumulation of ice caused a repeated 'tipping' of the Earth's axis every 5,000 to 7,000 years or so. He argued that the 'wobble' of the Earth on its axis, combined with speculation that the crust slides on the mantle, meant that a shift was imminent, and even suggested that the polar ice caps should be broken up using nuclear explosions, in order to stem the accumulation of mass at the poles, which Brown thought could overbalance the Earth on it's axis, shifting the axis of rotation.

This is not to be confused with geomagnetic reversal, or plate tectonics and other associated theories, but refers only to the sudden, cataclysmic shifting of the Earth's axis of rotation.

Another early proponent, Charles Hapgood, in his book 'Earth's Shifting Crust', suggested that the accumulation of ice at the poles could somehow 'overbalance' the crust, breaking it free from the mantle and causing the crust to slide into a new position, leaving the axis of rotation essentially the same, but with the crust adopting a new position. A foreword was written to this book by Einstein, who was quite excited by Hapgood's writing.
I frequently receive communications from people who wish to consult me concerning their unpublished ideas. It goes without saying that these ideas are seldom possessed of scientific validity. The very first communication, however, that I received from Mr. Hapgood electrified me. His idea is original, of great simplicity, and-if it continues to prove itself-of great importance to everything that is related to the history of the earth's surface.

Of course, this was before the development of plate tectonics, and Einstein had concerns of his own:

Without a doubt the earth's crust is strong enough not to give way proportionately as the ice is deposited. The only doubtful assumption is that the earth's crust can be moved easily enough over the inner layers.
In 1998, retired engineer James Bowles, proposed a mechanism, which he named 'rotational bending', a process that involved the gravitational pull of the Sun and Moon pulling the crust at an oblique angle. This wore away at the underpinnings that linked the crust to the mantle, and generated a 'plastic' zone that allowed the crust to move in relation to the mantle, and allowing the poles to migrate to the equator.[5]

The scientific evidence suggests that, although polar wander does occur[6], it occurs at a rate of less than 1 degree in 1 million years. The last conjectured rapid shift was around 200 million years ago.

Reality

I want to use the remainder of this essay to discuss two scenarios that have some basis in reality.

Viral pandemic

It has long been known that there are micro-organisms capable of ending it all for humanity. In the early 14th Century, bubonic plague swept across Europe, wiping out a third of the population. It originated with the marmot of the Gobi desert, passing to fleas, rats and eventually humans. Returning every generation or so until the 1700s, it is thought that the plague killed in the region of 200 million people in all, although there is some debate about whether all were killed with the same disease. It was almost certainly largely responsible for the collapse of the feudal system in Europe, to at least the degree in which 'serfs' began to have some economic clout, owing to the massive shortage of labour left in its wake. [7]

In the last two centuries or so, medical science has brought us some relief from such micro-organisms, beginning with Jenner's early experiments with cowpox as vaccination (from the Latin vacca – cow) against smallpox in 1796, and leading up to the development of antibiotics, stemming from Fleming's discovery of penicillin in 1928. Our reliance on antibiotics these days is more than apparent, but it brings with it its own problems.

One of the major current threats to our health today is the increasing resistance of micro-organisms to antibiotics. Beginning with one that I suspect all of us have heard of, due to its recent coverage in world news, namely MRSA.

MRSA, or Methicillin-resistant Staphylococcus aureus, is a strain of Staphylococcus, a bacteria that has developed a resistance to conventional antibiotics. Initially, Staphylococcus was treated with Vancomycin, a glycopeptide antibiotic first isolated in the jungles of Borneo by E C Kornfeld, but Vancomycin was never used as a first-line treatment, because it had to be administered intravenously, and it was subsequently supplanted by methicillin. Further, early, impure extractions of Vancomycin were shown to be toxic to the ears and kidneys.

In recent years, strains of MRSA have emerged that have developed resistance even to Vancomycin, and in reality we are running out of ideas in dealing with them.[8],[9]

It is also fairly certain that there are as yet undiscovered micro-organisms that pose a significant threat, especially in the modern world, in which international travel is ubiquitous, and viruses can be spread across the planet in a matter of days.

Bolide Impact

This is going to feel a little like cheating, but the following is what actually inspired this essay.

Probably the single biggest threat to life on Earth, notwithstanding climate change and the aforementioned pandemic, is that which is widely regarded as having brought the age of the dinosaurs to an end.

In 2005, US Congress mandated NASA to identify 90% of large Near Earth Asteroids (NEAs) by 2020. In a release yesterday, 18th February 2010, Alexis Madrigal, writing on behalf of the UK's Spaceguard Centre, discussed a report, Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies , released by the National Research Council, in which it was suggested that this is not an attainable goal with current technology and funding. In reality, it is not actually known how many such objects are up there, and estimating the risk to humans is problematic. Michael A'Hearn, of the University of Maryland, writes:

Our estimates of the risk could easily be wrong by a factor of two or three, I don’t think they are wrong by a factor of 10, but the boundaries, again, haven’t been explored.” [10]
He also discusses the problems of understanding the physics of an impact, saying:
The first thing we need to do is understand what the hazard is. That’s partly finding them and partly understanding what their effect is. We have to understand in more detail how we’d mitigate against them.
Recently discussion arose in which a particular poster was discussing what he thought would be the best traits granted by evolution in the event that four (count them) Texas sized bolides were heading for Earth from different directions. He was suggesting that intelligence would grant the best strategies for survival. Given that mathematics is not my strong point, I asked Calilasseia if he would mind doing some back-of-the-envelope calculations with regard to the thermodynamic exchanges involved in such an impact, and he has kindly given permission to use them here.

The volume of a bolide the size of Texas is given by:

$V = \dfrac{4}{3}πr^3$ where $r = 622,000\ m$

This gives us a value for the volume of our bolide of $1.008 \times 10^{18}\ m^3$.

Now, to make life simpler, let's assume that we're dealing with an iron meteorite. Iron has a density of $7,873\ Kg/m^3$ (Source: the properties of the elements table from Kaye & Laby's Tables of Physical & Chemical Constants), therefore an iron meteorite will have a mass of $7.936 × 10^{21}\ Kg$, to a reasonable level of approximation. A more precise calculation would take into account that an iron meteorite actually contains around 6.7% nickel (source: the abundances of the elements table from the same source as above), and since nickel is denser than iron, leaving it out means that we're underestimating the mass, and erring on the conservative side again. By comparison, the mass of the Earth is $5.9736 \times 10^{24}\ Kg$, so we're dealing with a body that is $0.13%$ the mass of the Earth, which means that already, it's a significant mass.

Bolides typically move through space at speeds of around 20 Km s-1, and so, we can calculate the kinetic energy of such a bolide once we know its mass, courtesy of $E = ½mv^2$. Feeding m = $7.936 × 10^{21}\ Kg$ and $v = 20,000\ m/s^{-1}$ into this formula, we arrive at a value for the kinetic energy of $1.587 × 10^{30}\ J$.

Now, if a bolide of this mass impacted the Earth at that speed, and atmospheric braking wouldn't do much to slow it down, a significant fraction of that energy would be converted to heat upon being brought to a halt in an inelastic collision. Even if we assume conservatively that only 50% of that energy is converted to heat as it impacts the Earth and comes to a halt, that still leaves us with $7.935 × 10^{29}\ J$ to play with. By comparison, the Tsar Bomba, the largest thermonuclear weapon ever tested in the atmosphere by humans, was puny - it had a yield of 50 megatons, or $2.1 × 10^{17}\ J$. Therefore, if a bolide the size of Texas impacts the Earth, it will yield as much heat energy as 3.779 trillion Tsar Bomba H-bombs.

That amount of heat energy is going to have some significant effects to put it mildly. Let's assume for the sake of argument, again a radical simplification, that all the heat energy is dumped into the bolide mass itself, prior to transfer to the surroundings. Iron has a specific heat capacity by mass of $442\ J/Kg^-1/K^{1-}$, which is the amount of heat energy required to raise the temperature of 1 Kg of iron by 1 Kelvin. So, to derive the temperature change $T$, given a specific heat capacity $C$, a mass m and an energy input $E$, we have:

$T = E/Cm$

Feeding our data into the formula above, we have that the temperature change of the bolide will be approximately 225,000 K.[11]
Obviously, this is an extreme example, and just a bit of fun here, but the risk is very real. Cali sums up with the following, which seems a good place to leave this topic.
I'd say that if just one bolide the size of Texas hits Planet Earth, we are, not to put too fine a point on it, fucked.
Refs:
[1] The End of Time: The Maya Mystery of 2012 : Anthony Aveni 2009
[2] http://en.wikipedia.org/wiki/Zecharia_Sitchin