Our Closest Call

I'm going out on a limb here but I'll predict that the world will not end on December 21, 2012. The Mayan calendar does end on that date but that is about all that does. The hype surrounding the Mayan calendar sold a few books and spawned a few apocalyptic movies. But nothing, literally, is on the horizon that would support the end-of-world premise.  We do not appear to be heading for an extinction event this year.  But through the long history of our planet, there have been at least five extinction events, i.e., periods during which the majority of species are made extinct. Over the past 500 million years, these have occurred an average of once every 100 million years. 

The most famous and most recent, but not the most destructive, of these events occurred 65 million years ago. The asteroid strike in the Yucatan caused the end of the age of the reptiles including the destruction of the dinosaurs. Discovered in the late 1970's, the Chixculub crater measures more than 110 miles in diameter. It is both a reminder of the fragility of life on this planet and of the good fortune of the small mammals that survived and from which humanity eventually evolved.

The most destructive extinction event occurred about 250 million years ago. “The Great Dying” saw 96% of all ocean species and 80% of all land species extinguished. Although we cannot be certain, it appears that this event was likely a combination of events. Possible culprits include a nearby supernova, environmental changes wrought by the formation of a super-continent, the devastating impact of a large asteroid -- or some combination of these.

Bad as these events were, they were not mankind's closest call. That honor goes to the Lake Toba Volcano eruption about 73,000 years ago. Looks pretty peaceful now, doesn't it?

(Photo is from the Wayfaring.Info website.)

Don't be fooled by Lake Toba's current placid appearance. Seventy-three thousand years ago, an eruption here in northern Sumatra in Indonesia led to a ten-year “volcanic winter”. The Toba event is believed to be the most powerful volcano in the last two million years. It spewed out 28 times the debris of the largest historically recorded volcanic eruption at Mount Tambora in 1815. The Mount Tambora eruption led to “The Year Without a Summer” in 1816, so called because of its impact on North American and European weather.

The Toba eruption and the ensuing “volcanic winter” reduced the human population to as low as 1,000 breeding pairs scattered in small pockets across the globe. Had the eruption been stronger, mankind may have been completely wiped out. I wouldn't be here writing this nor would you be there reading it. What species would take our place? Would the Earth have to wait another 2-3 million years before another land mammal evolved to reach the threshold of self-conscious intelligence? Would dolphins or whales evolve to fill the “consciousness” niche? If so, would a water-based intelligence be capable of creating a technological society? Would dinosaurs make a comeback? Would a hive mind eventually achieve higher intelligence? Or would the Earth remain forever devoid of self-conscious intelligent life?

So back to why the world won't end come this December. Looking over the extinction events of the past half billion years, we see that they were due to massive climate shifts or to large changes in ocean levels. These climate and ocean level shifts were caused in turn by several types of large-scale catastrophic events – changing supercontinent tectonics, volcanic eruptions, supernovae, and asteroid/near-Earth-object impacts. 

Supercontinent tectonics shouldn't come into play any time soon - the supercontinent implicated in the “Great Dying” formed some 300,000 years ago and had the land mass of all the existing continents combined.

While it's impossible to predict massive volcanic eruptions, suffice it to say that the Lake Toba eruption was the largest in at least two million years. 

 

As for a supernova (an exploding giant star) wiping out the Earth, if the dying star is close enough and massive enough and has a suitable companion star, there is nothing that could possibly stop it from bringing civilization to an end. The good news is that the most likely nearby star that can cause this devastation is predicted to go into its final death phase in 10,000,000 years.

 

Near-earth objects then are probably the most likely short-term scenario for wide-spread earthly destruction. There are about 1 million asteroids of a kilometer or more diameter and there are 10,000 asteroids of the size that brought down the dinosaurs. Near-Earth objects are already monitored and tracked closely by NASA and others. Contingency plans are being developed for how to deal with any threats. These plans generally involve nudging the asteroid slightly off its collision course. There are a couple of potentially destruction-wreaking NEO's in our future but we have decades to prepare:

• On April 13, 2029, asteroid 2004 MN4 will fly past Earth only 18,600 miles (30,000 km) above the ground. For comparison, geosynchronous satellites orbit at 22,300 miles (36,000 km). This is a 300 meter asteroid and could take out an area the size of Texas if it hit. As of now, though, astrophysicists are saying that it has no chance of hitting the Earth.

• The 460-foot asteroid 2011 AG5 is estimated to have a 1 in 625 chance of hitting the Earth on February 5, 2040. For comparison, the asteroid that flattened the land around the Tungaska River in Siberia in 1908 was 30-60 ft in diameter.

So it doesn't appear that we should fear extinction as a species anytime soon. Of course, we can always destroy ourselves quickly in a nuclear holocaust or slowly with unaddressed global warming. And what a waste that would be.

A Note for Sci-Fi Fans

I love speculative fiction. It deals with the most mind-boggling concepts imaginable in an engaging way. For an interesting read on a universe where dinosaurs are the dominant intelligent species, see Robert Sawyer's Quintaglio Ascension Trilogy (Far Seer, Fossil Hunter, Foreigner) . Orson Scott Card's Ender's Saga (particularly Ender's Game, Speaker for the Dead, Xenocide, and Children of the Mind) provides, among many, many other things, an exploration of the intelligence of a hive mind. Intelligent dolphins appear several times in David Brin's Uplift anf Uplift Storm trilogies, most notably in Startide Rising. Finally, Charles Sheffield's Aftermath shows the havoc resulting after Sol's nearest neighbor, the twin star system at Alpha Centauri, goes supernova.