katbolideimpact

Bolide Impact:

Bolide impact theories are often the flashiest theories for mass extinction because it eliminates many problems like those of other theories. Think about it: if something really big falls from the sky, it’s going to kill everything around it and cause worldwide chaos and destruction; then there’s no need to worry about dealing with combinations of unproven factors and it sounds really cool.

From Brenchley’s Palaeoecology: Ecosystems, Environments, and Evolution, the correlation between bolide impacts and mass extinction is as follows:

Late Ordovician: reported Iridium anomaly around time of extinction but no confirmed on re-analysis.
Late Devonian: several weak Iridium anomalies and microtektites and at least three known impact craters dated to the Devonian.
Late Permian: Iridium anomaly found in China but no where else.
Late Triassic: Manicougan (Quebec, Canada) impact crater dated to the late Triassic
Late Cretaceous: over 50 sites with reported Iridium anomaly, microtektites, and shocked quartz.

From this analysis, the bolide impact theory bears extreme relevance to the Late Cretaceous extinction because it demonstrates the most evidence for impact. Therefore, how does a bolide impact relate to rapid climate change and mass extinction?

Bolide impacts can cause rapid climate changes. Since the Late Cretaceous extinction was affected by the bolide impact, it will serve as the example. In the Late Cretaceous extinction, it is projected that the meteor split in two pieces and struck around the Caribbean area and in Manson, Iowa. The meteor, after landing, would have sent up lots of earth and bits of the meteor, meaning lots of matter and dust particles. Some of the matter would escape the earth’s atmosphere but others would not and fall back to earth in the form of fireballs that triggered massive wildfires, and "over half of the earth’s vegetation burns in the weeks following the impact." (Ward, 1989) It’s rather obvious that fire would not be conducive to life…

Immediately following the impact, there would be an extreme amount of thermal energy released as well as the heat loss from the depths of earth (Snowbird Conference, 1981). This would result in a shock heating of the atmosphere. This means that atmospheric oxygen and nitrogen combined to form nitrous oxide. When nitrous oxide and water are combined (water in the form of rain), this produces nitric acid in the rain, also known as acid rain. According to Ward, acid rain continued following the impact "till the upper 300 feet of the world’s oceans are of sufficient acidity to dissolve calcareous shell material." Also, the acid rain is projected to be of extremely high acidity, with a pH as low as 1 or 0 (Newton, 1989). Organisms that live in the oceans, especially the ones that remain relatively close to the surface for sunlight would suffer due to high acidity. So, environmental conditions are immediately in disarray because of vegetation losses, initial heat, and acid rain. Organisms that rely on vegetation, cannot adjust to warmer temperatures, and cannot take acid rain would be immediately affected by this, and most likely would result in their deaths.

Of course, the climatic effects did not stop there. Even after all the dust cleared, the earth heated beyond the normal temperatures before the bolide impact. Temperatures climb, "for the impact has released enormous volumes of water vapor and carbon dioxide into the atmosphere, creating an intense episode of greenhouse warming," according to Ward. Switching from a global cooling from darkness to global warming qualifies as rapid climate change and would have adverse effects on organisms that were adapted for a mainly warm, but not hot, environment.

However, with the atmosphere full of particulate matter and smoke from the fire, the solar radiation would be blocked, thrusting the earth into a period of darkness. The period of darkness has been projected to have last anywhere between 3 months, the Alvarez projection, (Ward, 1989) to months and even years (Newton, 1989). Darkness would cause the temperature to drop over a relatively warm environment. The evidence for this comes from a lower ?13C ratio, showing there was much less photosynthesis taking place; therefore this is further proof that darkness and decline resulted from the bolide impact (Brenchley, 1998). More evidence pointing to the adverse effects of darkness is found with vegetation. Scientists noticed an adverse effect on evergreen taxa: before the impact there evergreens were quite dominant but after the impact, deciduous trees were dominant. This shows that having the ability to become dormant was an excellent advantage because darkness hinders photosynthesis. (Chaloner and Hallam, 1994) Organisms that rely on photosynthesis would most likely perish along, and this would travel up the food chain, to organisms that rely on photosynthesizing organisms and on up.