Thursday, August 13, 2015

Extinction Events and Planetary Perils

Perils, which are possible events which cause an alien civilization to have to migrate or face extinction, come from three categories. Galactic perils and solar system perils have been discussed elsewhere. In an attempt to determine possible reasons why there are no aliens flying around Earth, we might also consider planetary perils, which are wholly localized to the planet the alien civilization is based upon. One source of them is the fertile thinking that has gone into understanding extinction events here on Earth.

Extinction events are not things which have directly affected us or our recent ancestors, but rather the known extinction events are focused on marine animal life, which appears better in the fossil records than land life or marine plants. The existence of extinction events is still somewhat controversial, as the fossil record has some ambiguities, but it seems there is sufficient evidence to warrant much thought about what the types of events are. Even though these events are rare, if they occurred during the period when an alien civilization was reigning on their planet, they might have to take drastic action to preserve themselves, or rather, to preserve their civilization.

The usual way to approach this is to focus on root causes, if such things can be isolated. A root cause is the initial precipitating event that causes other things to happen, and this second round of things might be the ones that cause the extinctions or lead to third round things which cause the extinctions. Extinction thinkers have several categories of planetary peril factors, including global cooling, global warming, atmospheric opacity increase, oceanic poisoning, atmospheric poisoning, or, surprisingly, evolutionary changes.

It is not very clear how to divide things into rounds, however, both because there is often a prior cause which led to what you were going to call the root cause, and because there are often multiple possible causes for some next round cause, and the predecessors might be round two or three or whatever. So let’s just think of chains of events instead.

Consider global cooling, meaning ice ages. One of these can lead to a drop of sea level, which uncovers much of the coastline and the continental shelves, and thereby eliminates the habitats of a large portion of marine animals, our target specimens for finding extinction events. Global cooling can also reduce the living area for species, and directly injure their food chain. Global cooling can possibly result from simply an change in the stable alternative of the global climate. Climate is a multistable system, meaning it can rest temporarily in one of several states, and then only gradually, or upon some external event, move to another state. One state is ice age and another is the opposite, which doesn’t have any similarly short name. Call it the no-ice age, as it is defined as a situation where all the glaciers has melted. This is the predominant state of the Earth, by the way. Glaciers are a temporary thing at best.

Thus, climate variation of a very independent variety can be a global peril, and specifically, the start of an ice age drains the continental shelves, causing the extinction of huge numbers of species around the world. It does not only affect those which lived on the coastlines, but also those living in the deeper ocean but feed upon the coastal dwellers. How aliens might address the threat of an ice age, or at least the end of an interglacial, is discussed in another post, so let’s move on.

Global warming is another peril. One potential cause of global warming is flood basalts. These are massive events that have occurred on Earth about once every twenty million years. They are similar to volcanoes, in that magma from deep inside the crust flows to the surface. The difference is that a flood basalt may cover hundreds of thousands of square kilometers and be kilometers deep. There are many areas on Earth where these can be recognized. They can release, over a long period, large quantities of greenhouse gases, which linger in the atmosphere as well, extending the warming period. They would put an end to an ice age, but would also wreak havoc other than through warming. They emit dust which blocks sunlight, leading to a collapse of photosynthesis and a failure of food chains. They emit poisonous gases which directly kill or weaken both plants and animals. And of course, anything near the basalt flood itself would be destroyed.

Flood basalts are thought to arise from two causes. One is the rise of a large bubble of magma to the surface, much like the smaller bubbles that rise and cause volcanoes. These eventually penetrate the whole crust and flow over large areas. They also are thought to arise from continental drift, with one continent sliding up over another, causing stress elsewhere on the continent that leads to an eruption of the magma below. The interchange of material between the mantle and the crust is also involved.

A flood basalt event is a good example of a planetary peril that does not appear to be amenable to any mitigation by aliens, no matter how advanced they might be. They would certainly be able to monitor the crust and predict such events, and possibly do so long in advance, where long is measured in thousands of years. With several thousand years to prepare, moving all cities far from the flood basalt region is one alternative they might consider. Flooding by the melting of any existing glaciers might add to the problems created by a flood basalt. Changing global temperatures would not be a large problem for aliens living in climate-controlled large cities, and with an energy supply that is not affected by climate, depending on fusion of some sort, they could continue to persevere. The exterior of the cities might be laid waste, and any ecology or activity that they were doing in the exterior might be put in severe jeopardy. It might also interfere with resource extraction, meaning the cities would eventually run short, despite recycling.

Known flood basalt events on Earth have differed in scale by a factor of ten in size, and probably in duration, although duration is much harder to estimate than size. The other alternative, possibly more realistic, for an alien civilization is to emigrate to another planet, rather than endure millennia of eruptions of a flood basalt. Thus, it is not only supernovae or star death or flux increase that might lead to a train of emigrant spaceships, planetary problems alone can be a cause.

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