Friday, July 10, 2015

A Possible Great Filter – Asteroid Chicxulub

One of the more well-known scientific theories concerns an asteroid which slammed into Earth 66 million years ago, creating world-wide cataclysms, and leading to a decline in the major type of land animals, dinosaurs. Dinosaurs were kind enough to leave their bones behind, buried in rock for preservation, so that we have knowledge of a wide spectrum of dinosaur types. This means that they are a prime candidate for children’s toys and wide-screen videos, leading to a popularity that can only be generated by the presence of money-making opportunities.

The kids with dinosaur toys can ask their parents what happened to the dinosaurs, and if the parents are well-informed, they have the answer. An asteroid killed them. If you want to make a scientific theory that is close to universally known, make it so it answers toddlers’ questions. It doesn’t hurt that it involves a dramatic catastrophe of a magnitude almost unimaginable. The asteroid obliterated directly a portion of the planet, that around the Yucatan Peninsula, with shock waves and high temperatures, and caused tsumanis in all the world’s oceans. It threw up into the atmosphere vast quantities of dust which obliterated the sun’s rays for years. Plants did not survive. Many entire species of dinosaurs disappeared, with the herbivores lacking sustenance, and then the carnivores lacking herbivores to munch on.

The dramatic events of this impact have become well-known and a source for popular journalism, as well as scientific investigations related to the impact and its biological and physical effects. It serves as a motivation for funding asteroid tracking and some thinking about how to destroy the next asteroid that is found on a collision course with Earth.

It is also often prescribed as the event which opened the gate for mammals. At the time of the impact, fossil remains indicate there would some small mammals in the forests, running around to avoid getting stomped on by the dinosaurs. They were another prey for smaller carnivorous dinosaurs. But some mammal species managed to get through the follow-on disaster of the asteroid impact. Perhaps they were like squirrels and had stores of nuts and seeds hidden away that would get them through the era of hunger. Perhaps they lived on dead vegetation or were carrion feeders, and the prevalence of dead dinosaurs was a banquet for them. Certainly there are many other options that would explain how mammals got through one of Earth’s worst experiences, and then proceeded, over the next few ten million years, to become the dominant mobile life-form here.

The survival of mammals long-term after Chicxulub and the disappearance of dinosaurs leads to an impression that there might be no human beings, and no trappings of our civilization like science and Apollo and TV if Chicxulub had not happened. That qualifies it as a possible Great Filter.

Great Filters are one category of answers to the question of where are the aliens. Great Filters are things that happen to almost all planets, and prevent space-traveling, meaning interstellar voyaging, except maybe from us on Earth some time in the future. In this blog we also talk about Inverse Great Filters, meaning things which happen to almost no planets, and the lack of them prevents space-traveling. For convenience, we can regard Inverse Great Filters as a kind of Great Filter of the lack of something. So Asteroid Chicxulub might be called an Inverse Great Filter, because perhaps all other alien planets with life still have dinosaurs and are waiting and hoping for an asteroid to come by so they can get on with their evolution. Or we can say that the lack of an Asteroid Chicxulub is a Great Filter. Either way the meaning is identical. The idea is that a very low probability or very high probability event exists and works to block space-traveling.

Asteroid Chicxulub would not be a Great Filter if mammals would have evolved to replace dinosaurs even without it. In other words, if there are alternate pathways to the eventual goal of space-traveling that bypass a potential Great Filter, it is not one.

Do mammals at a primitive level possess evolutionary advantages over dinosaurs? Evolutionary advantages are reckoned in terms of three things: direct competition between the competitors, the ability of a competitor to fill another niche of the ecology which another competitor cannot, or the ability of a competitor to adapt more effectively to a change in circumstances, which might be a temporary change or a permanent one.

Dinosaurs of various types had ruled the planet, in other words were much more impressive models for children’s toys, for about 150 million years. They were competitive among themselves, were continually evolving, had been successful at different sizes ranging from the size of the mammals up to the largest mobile creatures ever to set foot on Earth, and had adapted to many different climates around the planet. Mammals weren’t like an invasive species often is on various areas of Earth today, coming in to some new area and having no predators and therefore reproducing like crazy and crowding out the native plants or animals. In the case of animals, invasive species may actually consume the young of native species and drive them toward extinction. Mammals weren’t doing that as far as we know. Perhaps they did eat the eggs of dinosaurs and that provided the necessary impetus to reduce the dinosaurs to what remains of them today. But almost all egg-laying creatures have predators which seek the eggs, and they survive the presence of these predators, either by concealment, by defense, or by numbers. So this feature is not conclusive at all.

Mammals, being warm-blooded, could hunt at night in cooler climates. This is a niche that might provide them an advantage to have outflanked dinosaurs and proceeded to differentiate and replace dinosaurs, at least in cooler climates. On the contrary. Nocturnal dinosaurs are known, filling this niche, and there is a school of thought which says dinosaurs were not cold-blooded in the same way as present day reptiles such as iguanas. So the advantage of warm-bloodedness might be only statistical, if at all, and perhaps not enough to prevail in the no-Chicxulub scenario.

With no Chicxulub, what other change of circumstances might show mammals as more able to cope than dinosaurs? Perhaps an ice age. Since they occur periodically, this might have provided the means whereby a mammal could have survived and a dinosaur could not.

Thus, there are suggestions as to why mammals would have prevailed without Chicxulub, but nothing conclusive without much more investigation. So it qualifies as a possible Inverse Great Filter, but won’t be able to be promoted to what we know is a real, effective barrier to space-traveling without a good bit more paleontology.

No comments:

Post a Comment