A collection of lecture, seminar and computer lab materials from Natural Systems courses at the School of Interdisciplinary Studies, Western College Program at Miami University, Oxford, Ohio 45056.

David Raup writes of three processes in his book "Extinction: Bad Genes or Bad Luck?" I think that the three processes, all of which are documented, have interacted to produce an extraordinary result on Earth. Come along with me as I argue the case for nucleic acids from hell.

The three processes as stated in Raup's book are:
1) Fair Play. This is the Darwinian sort of pattern where natural selection "rewards" well adjusted or adapted organisms with differential reproductive success (as seems fair to us). To check for an example in your family, consider that the number of grandchildren you or your parents have are a measure of this sort of success. Organisms which have lots of "grandkids" are more successful by this criterion than those that do not have many. Failure comes in a variety of forms, but less well adjusted genomes are replaced by the better adapted ones.

So---why isn't the planet packed with a phalanx of niftily adapted species and evolutionary novelty rare? Because the second process knocks holes in the first, leaving room for strange and wonderful things to happen. The second process is:
2) Field of Bullets. With this scenario, "virtuous" or adapted nucleic acids (DNA, RNA) and "valueless" or problematic nucleic acids get wiped out in nasty little accidents (chance). Depending on the balance between fair play and field of bullets in a given geologic era, this keeps opportunities open for novel evolutionary events.

And then, the really outstanding way to die on this planet:
3) Mass Extinctions. It would appear that life, for which there is evidence, is at least 3.6 billion years old. Recent microfossil finds of embryos dividing indicate that multicellular life is about 600 million years old.

So what was life doing for 3 billion years? Was it just inventing clever biochemistries to use all sorts of substrates as food? Yes and no.

Until about 600 million years ago, there may have been too many closely spaced mass extinction events (asteroids and other accidents) for fancy organisms to develop. Then there was about a 100 million year spacing of mass extinction events which we know as the Big Five. Two (Devonian and Cretaceous-Tertiary) have been attributed to asteroid hits. The whopper extinction (Permian) may have been an ocean overturn, possibly at a time when continental configurations made the world ocean especially sensitive to warming or cooling trends. Very nasty, as flipping over the ocean (think of a summer or winter stratified pond) would bring all that deep layered oxygen minimum gunk to the surface, poisoning the oceans and atmosphere.

The outcome of Fair Play and Field of Bullets acting between Mass Extinctions may have been to produce increasingly responsive, resilient gene pools with each iteration of extinction and recovery. After all, disturbance is the norm on this planet. Each time a section of the biosphere was erased in a mass extinction, the organisms which came back to fill the empty niches were factors in each other's evolution. The output of each cycle is input for the next. So we should expect adaptability to be characteristic of present genetic codes (especially viral codes, which play the evolutionary numbers game very well).

But back to asteroids. There appears to have been a planetary demolition derby from early days in our Solar System. The moon may have orginated from a major collision with a sub planetary mass. The main asteroid belt has intriguing rocks: are they chemically differentiated in ways that argue for their origin in a busted planet? Or are they an unfinished piece of planetary evolution? Are the Near Earth Asteroids (Aten, Amor, Apollo swarms) of the same origin? Are they debris left over from the bad old days when the young Earth got whacked so hard that only microbial life endured? Stay tuned to this channel for ways to probe possible answers.

Anyway, the animation begins with the 20 kilometer asteroid heated from friction with the atmosphere. Its shockwaves ignite the air (nitrogen and oxygen), fry the biosphere, boil the ocean near shore and shatter rock (calcium sulfate/gypsum and calcium carbonate/ limesone).

Then the rock itself hits, melting continental crust, splattering molten chunks of planet into space (not shown. BUT IS THIS HOW LIFE GOT TO MARS FROM EARTH LONG, LONG AGO?), creating a dandy tsunami and then boiling off the ocean over the melted sea bottom. The rain of molten glass beads, sprayed over what was to be the southern USA, is below the resolution of the movie. A tsunami can be seen rippling out, scouring ocean floor along the continental shelf (and headed for coastline mayhem just about everywhere).

Meanwhile, the regional biosphere has been incinerated and appears as smog mixed with steam from the boiled ocean. The final frame shows the molten but congealing complex rippled crater before 65 million years of continental drift and erosion filled it in. I will leave corrosive effects of the acid rain from boiled ocean plus vaporized calcium sulfate (sulfuric acid), calcium carbonate (carbonic acid) and cooked air (nitric acid) to your imagination.

I had to leave the atmosphere somewhat transparent so the events can be viewed. There is more stuff which could be animated, but it adds to render time, so I left it out of this movie. Maybe later...

Where is the crater geographically? Centered at the town of Progresso on the Yucatán peninsula. Inflections on the coast match the ripples of the crater. However 65 million years of erosion and continental drift has obscured much of the structure. It turns out that satellite radar images have revealed an arced pattern of the cenotes (sacrificial wells) used by Central American civilizations: the arcs follow the outlines of the crater.

Below is an estimate of the Late Cretaceous climate and the positions of the continents. There was bitter cold at the North Pole (which has drifted from its ancient location to where it is now) and Gondwanaland was fairly nice. Lucky Gondwanaland (Antarctica plus Australia) to be away from the hit! The low angle entry, which dug a trench before the asteroid embedded itself in melted crust, is oriented along the (underwater) axis of Yucatán of 65 million years ago. I speculate that this means a Near Earth object as a likely source for the asteroid. However, it could have been a chunk of rock from somewhere else in the Solar System.

The hit is at the worst possible place to create devastating tsunamis and to vaporize a large portion (perhaps up to 70 %) of the biosphere. It is also possible that once more than 10^15 metric tonnes of dusts had cleared from upper and lower atmosphere, climate over land no longer was influenced by substantial vegetated areas. Further studies on ocean cores and well cores will help make the consequences of the hit clearer.