pre-Cambrian survival

I never knew  -  ‘till Kalamazoo

What did I not know until Kalamazoo?  There is a tremendous amount that I didn’t know, and still don’t.  But that is probably true for most of us.  What I am talking about is some of the events related to how we evolved over the past two billion years to become the dominant species on earth.  Our knowledge of evolution is riddled with gaps and errors, even though the general story of evolution by natural selection is probably close to the truth.  The last section tells of three important ways marine species may have been able to survive the intense extended period of pre-Cambrian asteroid bombardment.

Many that believe in God reject evolution because the sequence of chance and random events are not acceptable as work of a creator conforming to their concept of God.  Many scientists, especially biologists, have found it difficult to accept God as the creator because acceptance is not compatible with their concept of the chance and randomness involved in evolution.  Both may struggle with the chaos, disasters, evil, and other bad things they see in the world and want to blame God, or see it as evidence of God’s non-existence.

Stop for a moment, and think about something in your life that seemed bad, but in retrospect you see that it helped make you who you are.  There are numerous such occasions in the evolution of life that may have been essential for evolution to take its peculiar course over the last billion years it took to produce Homo sapiens.  If that doesn’t inspire you, read on, find out how important extinction events were in the course of evolution leading to us.

THE FIRST TEN BILLION YEARS

The “Big Bang” begs a question like the one asking “is there is a noise if a tree falls in the wilderness and there is no one there to hear it?”  Astrophysicists have an answer for the projected rapid expansion from the first relative speck to the slowing expansion, formation of elementary particles, elements, and the first generation of stars.  Condensation of materials into later generations of stars (after the extinction of some early ones) was responsible for the formation of heavier elements completing the materials needed for the evolution of life on planets with favorable conditions around stars like our sun.

We don’t need to know the details of the formation of our solar system.  It was probably similar to a billion other places of the expanding universe.  Whether the protoplanetary disks around the stars formed by condensation of more diffuse matter, or from emissions or explosions from the newly formed stars, sufficient matter ended up forming planets spinning and orbiting the sun.  Some planets had sufficient gravity to retain gases in their atmosphere and retain space debris striking them.  Planets tend to collect most of the debris as well as larger objects in their orbits.  The larger objects sometimes were captured in orbit as moons or impacted the planets with varying results.  The sun, with its massive gravity, probably collected many objects, even planets, that lost speed due to some collisions and fell into the sun.

Our moon does not have seas and atmosphere like the earth, so erosion has not obscured the craters produced by impacting meteors, comets, and asteroids.  In fact, the moon may have provided some protection to us from some that would otherwise have hit the earth.  Craters are much more numerous on the far side of the moon than they are on the lava fields of the near side.

Some worry more than necessary about the danger of an asteroid causing our extinction as part of a phenomenon much like the events terminating the dinosaurs.  It is remotely possible, but the solar systems planetary arrangement suggests that a much more stable system exists than the state several billion years ago.

Where would we be without asteroids?

 The irregular structure of some asteroids and craters or “pock marks” shows they had been stuck many times.  The presence of many moons and smaller satellites around the four largest planets, all beyond Mars, suggest that some were captured as moons and perhaps the collision with potential moons and or planets may have provided the fragments (asteroids) of the asteroid belt orbiting in space between the orbits of Mars and Jupiter.

Some of those fragments provided extinction-type events in decreasing frequency as they were swept up by earth, the moon, adjacent planets and their moons.  In the beginning impacting asteroids contributed mass to the earth.  They probably sped up some of the potential chemical evolution steps in the pre-biotic earth.  Perhaps their craters filled with water to make many experiments in addition to the intertidal pools where the chemical steps leading to organic life may have started. 

How life survived asteroids

The late pre-Cambrian is thought to have experienced a long period of more intense asteroid impacts.  The abyssal sea was so great a portion of the earth’s surface layer, and the cold polar seawater flowing toward the equatorial region had high density due to temperature and salinity that allowed it to gradually replace bottom water.  The process continued taking thousands of years to have bottom water reach the surface, just as happens today.  Animals able to adapt to the abyss had such an extensive area to inhabit it enabled some to survive even the worst asteroid hits.

A second method was the selection of cysts and other survival mechanisms used as overwintering, drought resistant, and dispersal stages that can emerge from somewhat suspended animation when conditions improve.  Such stages were already being selected by the rigors of surviving dry periods in freshwater temporary ponds as well as in saltwater pools along ocean shores.  Gemmules of sponges and statoblasts of bryozoans are cystlike asexual reproductive bodies, common among freshwater species but missing in marine species, suggesting such survival mechanisms are now less valuable for marine species in their more stable environment.

A third method is direct uptake of nutrients dissolved in seawater.  The mortality of marine species may well have boosted the dissolved organic matter content of seawater following an asteroid extinction event.  It may be an important method in today’s oceans for the survival of larval stages during dispersal, especially in species providing little yolk for nutrient reserves for the larvae.  Stephens, Grover C., and Robert A. Schinske  (1961, Limnology and Oceanography, 6:175-181.)  found that in ten phyla tested only arthropods did not take up amino acids from very dilute solutions in seawater.  Manahan and Crisp (1982, American Zoologist, 22:635-646) found dissolved amino acids could be taken up by bivalves from egg to adult stages.

The pogonophora benefitted by their living in the abyss, a relatively protected location of such great extent that remnants of the population might survive.  They also benefitted from the third method of direct uptake of dissolved nutrients in sediment water.  The "degenerate" appearance of the pogonophorans is part of an evolutionary step backward that laid the groundwork for the advance of animals to today's vertebrates.

Joseph G. Engemann   Kalamazoo, Michigan    September 26, 2017

DINOSAUR EXTINCTION

DINOSAUR EXTINCTION

A quick Google search confirmed my impression that the dinosaurs became extinct about 65,000,000 years ago at the end of the Cretaceous.  An exception was indicated by referring to the extinction as not including non-avian dinosaurs.  That distinction was made to satisfy scientists who have determined that bird’s ancestral reptilian roots was most likely in a specialized line of dinosaur-like ancestors.  It seems to me that it is unnecessary to continually repeat that connection in discussing non-phylogenetic issues.

Birds are sufficiently different from dinosaurs that they deserve their independency as a group.  Feather’s, no teeth, and homeothermy (maintaining a temperature independent of environmental temperature) may be avian characteristics that had a role in the survival of birds, but that is another topic.

THE MAJOR CAUSE, AN ASTEROID STRIKE

Multiple causes may have operated in making dinosaurs unable to survive the asteroid strike(s) that produced world-wide evidence of the disaster in the geological record found in sediments.  Several other major geological periods ended with similar disruptions, all also associated with the extinction of a large percentage of previously existing species.

In the several billion years of the earth’s existence earth has grown by the impact of space debris of varying sizes as indicated by the assortment of craters on the moon and other planets   Such bombardment was so intense in pre-Cambrian times that animals left a very skimpy fossil record, partially because large fossil forming animals seldom evolved or survived.

The abyss as a refuge during extinction events

The one place that had relatively stable conditions during extinction events was the abyssal region of the oceans.  There, any animals that could survive on the nutrients deposited in sediments had a better chance of survival in some location because most of the earth was covered with deep oceans.  The deep-water pogonophorans were one of the survivors.  The oxygenated region was so extensive and so slow to be replenished by polar surface waters that much of the fauna adapted to the region persisted to the present.  Those abyssal conditions made low metabolic rates and extended life cycles contribute to a very slow, almost absent, evolutionary rate for animals living there. (see 2015/05 listed at end of this post)

BEYOND THE ASTEROID IMPACT ZONE

Direct hits by the asteroid, its fragments, debris blasted from the impact zone did not even have to kill a single dinosaur.  But the world-wide atmospheric debris may have persisted for a year or more and made it difficult for significant plant growth of the type needed by large herbivores.  Carnivorous dinosaurs like T. rex would miss their normal food after large herbivores starved.  Continents isolated by oceans and partitioned by deserts or mountain rages would have made it difficult for the large dinosaurs to escape the drastic climatic shifts temporarily making their existing range uninhabitable.

POSSIBLE SECONDARY CAUSES OF DINOSAUR EXTINCTION

Pre-strike population declines or increases may have contributed to the death of many species.  Such declines may have been in the dinosaur species and/or other groups important in their food chains and are not limited to food organisms but could include microscopic disease organisms, parasites, and competitors of various types.  

The complexity of population changes resulting from decline or increase of one species is difficult to predict with certainty.  The decrease in one species may result in survival of more of those they prey upon and fewer of those feeding upon them. The changes can ripple up and down the food, predator, and parasite chains existing in the ecological community.  Add to these changes each of the physical changes produced by each species and the variability of possible community changes becomes astronomical.  If the vast number of buffalos grazing on our prairies had not been replaced by cattle, sheep, and farmers plowing- would much of it reverted to forest or scrubby vegetation providing homes for a different group of animals and plants?  Such changes had far reaching effects including soil erosion, flooding, less retention of water and less rainfall; all changes having additional effects on climate and life.

The cooling accompanying the atmospheric debris which reduced light energy and it warming effect makes a possible sufficient cause for extinction of many dinosaur species by shifting sex ratios of eggs hatching to all of one sex.  It is known that alligators and some other reptiles deposit large numbers of eggs in holes that they dig in the ground.  The holes are then covered over and the deeper the egg in the ground the cooler the temperature it experiences during embryonic development.  Higher temperatures induce one sex, cooler temperatures induce the other sex.  If cooler temperatures make all become the sex normally found in the deeper part of the nest, all will be of one sex.  It is not known if the phenomenon is the cause of alligators being restricted to warmer latitudes.

Cooler temperatures would make animals other than birds and mammals become inactive and unable to respond to egg predation or even being eaten by smaller animals with feather or fur insulation and higher metabolic rates maintaining body temperatures needed for activity.  The immense size of dinosaurs made them less susceptible to short term cold temperatures because it takes days for the largest to cool down, but the asteroid caused global cooling would persist so long it might have been sufficient to cause their demise, even those many other causes may have speeded the process of extinction.

Joseph Engemann     Kalamazoo, Michigan     October 20, 2016

http://evolutioninsights.blogspot.com/2014/03/science-extinctions-and-evolution.html

http://evolutioninsights.blogspot.com/2015/05/abyssal-ocean-environment-and-extreme.html 

EVOLUTION: QUIET PRE-CAMBRIAN GENES

THE PRE-CAMBRIAN ENVIRONMENT AND ANIMALS

Genes of the Pre-Cambrian can be inferred from common genes and biochemical pathways shared by extant species.  But there is reason for saying that genes that have not left echoes of their voice had an important role in evolution as well.  Those quiet genes, sometimes important for their silence, can also be inferred from analysis of how some characteristics developed, especially the annelid theory of chordate origin that, I maintain, is the best explanation of origin of chordates via pogonophorans and hemichordates.

Introns and exons

Natural selection is effective in eliminating useless features because there will be no selective force maintaining them, other than the chromosomal duplication process.  The portion of the genome active in protein coding is thought to be about 1.5 percent.  The 98.5 percent of the DNA not active in production of RNA needed to produce structural and functional proteins and control substances may have some value in other ways that are less dependent upon their exact nucleotide sequence.  In comparison to human DNA Collins (2006) shows the sequence for protein codes is 100% the same as in a chimpanzee, 75% the same in a chicken, and 35 % in a roundworm; whereas random segments of DNA between the genes only corresponded at rates that were 98% for a chimpanzee, 4 % for a chicken, and -0 % for a roundworm.  Human to human DNA comparisons show about 99.9% identical DNA.

What happened to the fossils?

Very little fossil record exists for times before the Cambrian.  Because fossils of numerous phyla show up in Cambrian rocks, it is apparent that many important evolutionary events occurred earlier.  I will omit discussion of sponge spicules, and tubes that may well have been made by pogonophorans, to go directly to presumed jellyfish fossils.  Pre-Cambrian jellyfish fossils were in the form of doughnut-shaped fossils thought to be casts of sand filled cavities of the bells of jellyfish.

It is not surprising that more ancient fossils are not found because extinction-causing events were more frequent as our orbit was more frequently hit by intrusion into our orbit of asteroids.  Localized destruction was probably much more frequent than the era-ending type giving worldwide unconformity of rock layers.  Even dating of intermediate layers produced by those major events may be difficult due to destruction of potential fossils.  Large areas may have been wiped clear by the event, so dating of sediments above and below an unconformity my show very different times of deposition.  A blended layer might be deposited in such locations and provide an intermediate date of origin.

Surviving extinction

Jellyfish deprived of food have the ability to survive and use their own substance as they "grow" smaller.  In the process they are found to first absorb reproductive organs completely as they shrink in size.  When food becomes reavailable the organs are eventually regenerated.  The finding that corals preceded jellyfish (described in an earlier post) provides support for the polyp-medusa-planarian sequence suggested.

The illustration above indicates how the polyp released from a starving coral could drift free to survive burial by sediments.  Adaptations aiding survival eventually result in the medusa shown in side view above and top view below where a later series of extinction events, depleting planktonic food, selected forms descending to sediments with nutrition enabling them to eventually take on the planarian shape that enabled better bottom feeding.

The jellyfish would naturally invert from the polyp orientation because the ring of tentacles would have a higher density due to concentration of protoplasmic structures and the potential buoyancy of the bell having trapped air bubbles.

The above enabled survival of jellyfish because their sexual generation could provide widely dispersed larvae capable of colonizing new post-extinction locations in shallow waters they required.  On the other hand pogonophorans survived because the abyssal region they inhabit is so extensive that remnants of habitat survived and the sediments themselves were the source of nutrition capable of bridging a long period of no nutrient input.  Also the extinction event may have given a temporary boost to dying and sedimenting food organisms replenishing abyssal food deposits.

Remember the quiet genes

Pogonophorans apparently adapted to the very low food supply by reduction of unneeded structure.  They have been shown to be able to take up amino acids from sediment water at naturally occurring concentrations.  Even though selection is not maintaining the code needed for gut formation, its slow rate of deterioration shown by the percentage comparisons in the second paragraph, enough remained to provide a basis for selection of a new gut much more efficiently than totally new selection would have required.  Most of the segment formation of annelids was lost by pogonophorans as well.  But enough of the process code survived to make the repeated structures - ribs, vertebrae, muscles, blood vessels, nerves - of chordate systems exist.

If every gene were always expressed, it would be difficult to have the diversity of cells making up our bodies.  There must be a very sensitive mechanism capable of turning gene activity on and off.  The process must also be varied in slight ways and sensitive to internal and/or external environmental cues to make well-adapted organisms.

Reference:  Collins, Francis S.  2006.  The Language of God.  Free Press (Simon & Schuster), New York, NY.  295 pp.

Joseph G. Engemann, Emeritus Professor of Biological Science, Western Michigan University, Kalamazoo, Michigan        March 6, 2015

SCIENCE: EXTINCTIONS AND EVOLUTION

EXTINCTIONS

The Sixth Extinction by Elizabeth Kolbert was the subject of an interview with her by Brad Plumer of the The Washington Post published in our local paper on March 2, 2014.  I have not read the book, but the interview was quite informative.  The increasing rates of extinction caused by various impacts human populations are having on the survival of other species may be leading to the sixth major extinction event.

Previous major extinction events presumably were caused by major volcanic eruption episodes, asteroid impact, and possibly widespread glaciation events; all likely associated with climatic changes.  Her discussion of the concept of "catastrophism" suggested by Cuvier was dismissed over a hundred years before the 1980's suggested in her interview.  Catastrophism was just one of several theories for the cause of evolution and/or change in the fossil record already known at the time.  Darwin's documentation of the theory of natural selection was rapidly accepted by many scientists, even before the role of the genes was clarified, as an explanation for the cause of evolution.

From the interview I suspect she does a good job of discussing the causes of increased extinction rates thought to be a harbinger of a presumed coming sixth extinction.  The fact that there have probably been many more major extinction events than the five indicated does not detract from the main thesis of her book of a possible coming sixth extinction.

In chapter eight, extinction's role in evolution, of an unpublished 2010 manuscript (Evolution Insights) I note that, after discussing the end of the dinosaurs, "Other mass extinction events have been documented marking the end of the Devonian, Permian, and other periods.  The transitions from the end of one unit of geological time to another usually show an unconformity of rocks, perhaps caused by the physical disruption due to a major collision.  The demise of species may be more severe after a prolonged period having no disruption.  The interlude may enable many to become so specialized to constant conditions that they cannot survive major disruption of those conditions."

"After the extinction event, the survivors again specialize into additional new species that fill the vacant jobs of top predators and many smaller special niches  The survivors that provided the ancestral material for new species were likely to have been generalists or specialized in some way that may have contributed to their survival.  As food supplies become diminished, small animals may be favored over large animals in finding adequate food to survive."

NUMBERS OF SPECIES

Once the terrestrial flora and fauna was well established in the Paleozoic, the numbers of species are thought to have peaked at somewhat comparable levels prior to major extinction events.  Once the approximate maximum was reached following an extinction event, the numbers of species may have hovered near the maximum as old species die off in competition with new and better adapted species.  Others have speculated, on limited available data, that the average species survives for about a million years, with great variability of extremes in both directions.  The fossil record would seem to support the idea that there have been hundreds of time more species that have lived on earth than the maximum at any one time.


THE ORIGIN OF SEX

A time of more frequent asteroid bombardment during Precambrian times played a crucial role in evolution.  The role the evolution of the Pogonophora from early annelid stock has been discussed earlier in this blog site.  The possible role of the same type of rigors had an even earlier role in evolution of major aspects of the origin of sex. Found in the manuscript mentioned above, are the following quotations from the chapter eight section titled, "The early roots of sex, fusion for survival".

"The starvation of protists during the early life extinction events meant degrowth to eventual fatal levels if they could not eat another protist or, better yet, fuse with another to make a viable mass.  Perhaps the reductions during degrowth resulted in a reduced genome lacking essential genes.  Or continued reduction after fusion made the survival of only the normal single gene genome an outcome that over time developed the needed stable genetic controls."

"The things that chance genetic changes did to help the process occur over millennia may have been rapidly selected as those not fusing died or were eaten before the resumption of hospitable conditions.  Eventually the process was fine tuned as it became the gamete union restoring the appropriate number of pairs of chromosomes as we see in sexual reproduction today.  The reduction division of meiosis may have been selected for maintaining the proper gene numbers in fusion of ancestors over a billion years ago."

Supporting evidence from simple organisms included fusion of amoeboid stages in cellular slime molds, suctorian ciliate's abilities to directly incorporate the protoplasm of prey species of ciliates into their own protoplasm without formation of food vacuoles, and a presumed lack of immune rejection in simple organisms, evidenced by the symbiotic origin of mitochondria and cilia.

Extinctions events may also have caused release of abundant nutrients from dead and decaying organisms.  The nutrients could be in solution as absorbable compounds most organisms could utilize, or as particulate matter available to filter-feeders.  Species able to utilize those mechanisms effectively may not have been the ones fusing in the early development of sex, the stage of the process discussed occurred a billion or more years ago.

EXTINCTION PEAKS

The most outstanding research I am familiar with about the history of prior extinctions is:
Raup, David M., and J. John Sepkoski, Jr.  1986. Periodic extinction of families and genera.  Science, 300:1734-1737.
I measured their graph of extinction rate peaks and found that a regression line of the peaks reached 100% for extinction rates at the end of the Precambrian.  [I know that percentages aren't appropriate in calculating regressions, but I thought the use of the number as a proxy for actual numbers was informative.]  Far greater species numbers presumably go to zero in each genus or family that goes extinct.  Their data only cover groups that fossilize and are found in rocks of known ages.


Joseph G. Engemann           March 6, 2014

EVOLUTION

Evolution and Asteroid Strikes

ASTEROID STRIKES HELPED SHAPE OUR EVOLUTION

Where would we be without asteroid strikes? 
                                   

We might still be here, but we would look entirely different.  Bombardment with asteroids and other space debris was much more common a billion years ago.  At that time life in our ancestral line had reached a worm-like stage that also gave rise to some other forms less like our egocentric selves.  The bombardment had an enormous impact on the course of evolution.

When God created the universe it began as a speck over twelve billion years ago as we measure time.  That speck was endowed with the properties that would spawn several generations of stars and the galaxies we see today.  It had all the potential for the formation of elements and star systems with associated planets as well as the evolution of life as we know it.  Darwin realized this as the work of the Creator before events sped his drift into agnosticism.

I know, from the things science has discovered, some major things that answer a few major evolutionary questions.  It is not because of personal brilliance or planning that I know them.  It is not because of some revelation that I know them.  It is the result of an unusual set of circumstances which I, have blundered into and, now view as God’s direction of the chance events that made it possible for me to put the bits of the puzzle together.

In 1987 two paleontologists (Raup and Sepkoski) published a study of extinction rates that showed high peaks associated with major asteroid impacts.  A regression line, which I calculated from their data, projected back over half a billion years to the beginning of the Cambrian where it reached a 100% extinction rate.  That obviously did not occur because there are Pre-Cambrian fossils, some of which had remains looking much like tubes of pogonophorans, which still live in the abyssal regions of the ocean bottom.

Pogonophorans were able to survive the Precambrian bombardment because they had evolved by natural selection to survive by absorbing nutrients from sediment and lost many of the typical annelid worm features of their ancestors.  They even lost the mouth and rigid early embryological features of their ancestral annelids.  Some changes now evident in their descendants led to, among other things- our systems being upside down as compared to most worms, our fertilized egg’s ability to have each of the early cells survive as twins or multiple births instead of dying when separated, and our pituitary to have its peculiar blend of hormones (the endodermal and ectodermal tissues that form the pituitary couldn't have joined if the pogonophoran pharyngeal region had not been suppressed during the period the former circumesophageal nerves were fusing).

Biologists think ancestral forms are replaced by new forms and cannot be found unchanged today.  But pogonophorans, because of the peculiar features of the deep sea have extremely long lives as individuals and thus those that stayed there evolved very slowly.

Many astronomers have come to believe the moon (Wikipedia, moon formation) started as a result of a collision of the earth with another heavenly body.  They believe the probability is very minuscule, but why bother when it is obvious that the following is much more likely.  The asteroid belt consists of orbiting fragments from a collision of two or more planets, or a planet and another major object, in that region between the orbits of Mars and Jupiter.  The scars on the moon, other planets, and large asteroids show the evidence of past impacts.  This immense accumulation of space debris was sufficient to slow the moon’s rotation so gravity’s effect could bring it to zero rotation with respect to the earth.  The earth’s greater mass was sufficient to keep it rotating even though we probably received more mass from space than did the moon, slowing us from 400 plus rotations per year to 365.  Tidal friction is used to explain the slowing of rotation for both the moon and the earth; but, shouldn't it have been more dramatically slowed for the earth with its oceans if that were true?

So we have cleaned out most of the fragments in earth’s orbital path and have a much reduced probability of an earth shattering strike from outer space than in prehistoric times.  The relative peace with the reduction or cessation of celestial bombardment, the last really major event being the strike that helped end the dinosaurs at the end of the Mesozoic about sixty-five million years ago, left a partial void that was repopulated in part by survivors from the deep sea.  The process of re-population from the deep-sea was much more important as the Cambrian began.

Incidentally, the idea of annelid worms being in our ancestral line was much more popular a hundred years ago.  Our annelid ancestry was rejected because of the great differences in embryology of annelids as compared to the vertebrates and invertebrates sharing our ancestral line starting with the pogonophorans.  When genetic information helped us see that the embryological differences were not the complete answer, the old annelid origin theory was not restored.  DNA/RNA studies are excellent for determining the relationships of closely related organisms.  Nucleic acid studies, as currently performed, have not yet been refined enough to project distant relationships. We know more about distant relationships from other data for widely different groups.

Almost anybody can write a book.  I've written a manuscript for one explaining some of the above.  But it runs counter to popular opinion of most students of evolution.  Why?  Probably because few biologists today have time for the range of course work common in my generation.  I had to dig into the literature on pogonophorans to revise an invertebrate zoology text for a second edition that was published in 1968.  I found that they must live for several thousand or more years, thanks, in part, to my knowledge of marine biology.  I might not have realized that if I hadn't developed an interest in causes of longevity during my doctoral studies (at MSU) comparing Michigan and Tasmanian isopod crustaceans (thanks to a 1956 Fulbright Grant for study at the University of Tasmania).

So the obscure pogonophorans that weren't even known about a hundred years ago provide important clues.  They show up in odd places in molecular studies of evolution because they have changed only slightly genetically while more recent groups have changed greatly.  Thus the great differences between the extremes of more recent groups are greater than the difference between either of the extremes and the pogonophorans.  I know it is due to the ancestral position of the pogonophorans and their extreme length of life.  My evolutionary colleagues think it can be explained away as an anomaly called “long-branch attraction”.

If my argument that major asteroid strikes are remarkably less likely in the future than in the past does not comfort you, consider the following.  If strikes are random, the likelihood of a strike is directly proportional to the area considered.  The mid-February one exploded above Chelyabinsk, Russia. On average, for every 63 that hit Russia, the largest country in the world, only 36 would hit the United States; about 100 would hit Russia while 1 is hitting Michigan; Liechtenstein would get about one strike for every 100,000 to hit Russia.  Kalamazoo is smaller than Liechtenstein, so sleep well tonight.  If you are still worried, remember that the one hitting Russia is only about the second big one to hit in the past one hundred and five years, the other knocked down trees over a large area in Siberia.

Oh, by the way, the regression line that I calculated hit 100% extinction rate at the beginning of the Cambrian, if I remember correctly, projecting forward, it did not hit zero anytime soon.  But with strikes in our area likely to be about once every twenty million years there doesn't seem to be much to worry about if the injuries are no worse than in Chelyabinsk.

Joseph G. Engemann, Kalamazoo, Michigan, Emeritus Professor of Biological Science, Western Michigan University. 

This was written for, but not sent, to the Kalamazoo Gazette letters editor in late February. Edited 5/11/13.