Lessons from Travels: Mayan Civilization

by Carl Strang

As I recall from elementary school history class many decades ago, we were given the impression that Europeans brought civilization to the New World. That may be true if “civilization” is equated with European culture (i.e., circular reasoning). Today I look at such things biologically, and long have regarded civilization as the evolution of any culture that creates the illusion of division between people and nature. In general that means the construction of an architecturally elaborated space in a part of the landscape that has been cleared of its wild vegetation. It also depends upon the previous establishment of agriculture (artificial selection of certain wild plants and animals to the point where they are domesticated), which allows people so to concentrate their populations. By that definition, there were many civilizations in North, Central and South America prior to the arrival of Europeans. Today I want to focus on vestiges of ancient Mayan civilization I saw in Central America.

This is the view from a tall Mayan building at Tikal, in Guatemala. Today the surrounding space is filled with forest. If it looks familiar, it may be because this spectacular scene was included in one of the Star Wars movies.

Over the years, many Mayan towns and cities have been discovered buried in the vegetation.

This building was uncovered at a smaller site in Belize.

By measures of architecture, agriculture, the technology required to shape and move masses of stone, and the social organization needed to accomplish these things, Mayans were thoroughly civilized.

This building alone, one of several enormous structures at Tikal, is a wonder. The climb those people are making is very steep and up huge steps clearly designed to inspire awe.

They had written language and mathematics as well.

Mayan writing, designed to last.

Recent research suggests that the drought which ended this civilization may not have been extreme. All it took was a reduction in summer rainstorms so that the reservoirs dried out. The intensive agriculture needed to support so many people in cities collapsed. Over time, a vast region that had been cleared for civilization was reclaimed by the forest. At least there were remnants of forest sufficient to do the reclaiming.

Do I need to state the lesson plainly? These people did not have an inferior or faulty civilization. In every significant respect it was the equivalent of ours. They no doubt assumed, as we do, that the Universe supported them and their way of living, and it would go on forever (or at least until 2012, small joke there). Their huge concentrated population was balanced upon the climatic conditions that supported their technology. As we can see, that balance was easily upset. They had removed their forests, which in part set up the drought, the climate change, which defeated them. Their descendants survived because they could fall back on an earlier, more dispersed way of living, and they had not completely trashed their soil and landscape. Their population was in the tens of thousands, rather than billions.

Some of the Lessons from Travels are chilling.

Advertisements

On the Move

by Carl Strang

Yesterday morning as I parked my car at the Forest Preserve District’s Danada headquarters, a strikingly marked bird flew to the top of a shrub in front of me.

A northern shrike!

This always is an exciting bird to see, not only because they are uncommon winter visitors from the far North, but because of their dramatic behavior. When a shrike leaves its perch, it does not simply fly away, but rather drops and Accelerates! Going from a state of watchful rest to full speed in two wingbeats, the bird scribes a graceful line through the air as it rises to its next perch and instantly again is alert stillness.

Birds are on the move again, showing signs of shifting out of their winter patterns. This shrike probably had a winter territory somewhere else, or I would expect to have seen it sooner. The first red-winged blackbirds appeared a couple weeks ago. Dark-eyed juncos have moved out of their winter home ranges. Robins are showing up in small groups in places from which they were absent in recent months, and have begun to forage on the ground. The numbers remain small, but all these cases collectively signal the start of a season of change. Canada geese increasingly are in pairs rather than flocks. Great horned owls are well into incubation. Spring is coming.

A Snowy Friday

by Carl Strang

The forecast called for more snow than we got. Instead of a forecast 8 inches we got a wet 3 at Mayslake Forest Preserve, thanks to the overnight temperature’s dropping more slowly than expected.

I had an enjoyable lunchtime walk through the snowy landscape. The only price paid was a zonk on the head by a small icicle that fell from an overhanging branch.

The snow didn’t stop falling until mid-morning, so there was no overnight record of footprints. A coyote was active in the morning, however, in the north savanna near May’s Lake.

This front footprint is fresher than it might seem. The soil was saturated and soft, and the track was collapsing rapidly. The soft mud also makes this track almost dog-like, but that’s an artifact of the conditions. Note how the middle toes remain well in front of the side ones. I also have the advantage of seeing all the other tracks the animal had made.

If I read this track correctly, the coyote was putting on the brakes slightly while making it. Note how the soil is cliff-like and somewhat elevated at the front edges of the heel and toe marks. Everything looks symmetrical, however, so it appears to be a simple deceleration rather than a turn.

Killdeer Dossier

by Carl Strang

As in past winters I have been sharing my collected observations on various vertebrate species over the years. While this may have some value in providing information, and revealing how there can be a difference between one person’s experienced knowledge and the collective accumulation of information available through references, the main point is to encourage you to pay more attention to the familiar and to build your own knowledge base of personally gained information.

Killdeer

Killdeer

This plover generally occurs in large, short grass fields and pastures. It produces a loud “killdee” call, often repeated in clusters. Small downy young can produce this call at surprisingly loud volume. The parent has broken-wing distraction display. Practically all of them depart from northern Illinois and northern Indiana for the winter, but a few remained through the winter near open streams in pastures in south central Pennsylvania. Mudflats also are frequented for feeding purposes and in migration. Killdeers have a very smooth, rapid run over the ground.

Killdeer nests are simple scrapes in the ground, containing 4 mottled eggs. The nest site generally is chosen such that the eggs are well camouflaged.

4JL86. Jeffersonville, Indiana. A pair on a golf course ran ahead of me. They stopped about 20m away from me, and settled into small depressions in the lawn (small bare soil patches) exactly as though settling onto eggs. If I approached, they quickly got up and ran ahead of me; no eggs or young were there. If I approached very slowly, the bird slightly spread its wings and tail, and went into the broken-wing display.

15MR87. 3 calling killdeers flew high over Meacham Grove, west to east, the first of the year.

4AP99. First killdeer of the year I’ve seen in DuPage County.

1AU99. Swenson’s Road pond, Fermilab. A couple killdeers walked at the water’s edge in an upright posture, only occasionally reaching down to the surface.

Killdeers seldom enter the water.

30OC99. Several killdeers still are at Fermilab.

26DE99. A killdeer was on the shore at Lake Maxinkuckee, Culver, Indiana. Broken ice sheet pieces were floating along the shore, and there was some snow on the ground.

20OC00. Killdeers flew over the Maxinkuckee Wetlands, calling loudly as they flew over the area for an extended period of time. The flight seemed to be a display.

22OC00. Many killdeers were at the marsh in south Blackwell Forest Preserve (and only 1 at McKee Marsh in north Blackwell). Two appeared to be involved in an agonistic display, standing a few inches apart and bowing forward until their breasts nearly touched the ground, calling, holding their tails straight and sometimes fanning them, sometimes pacing around. Once one appeared to bite or peck toward the other.

The killdeer’s long tail, folded here, is largely a bright reddish color.

21JL01. Fermilab. Half a dozen killdeers at the Swenson Road pond are mainly staying well back on the drier mud.

13NO01. A couple killdeers still are at Rice Lake, Danada Forest Preserve.

1AU04. Greene Valley. A shallow large pond at 83rd Street and Rt. 53 has attracted many shorebirds. Pectoral sandpipers nearly all are feeding in the shallowest water with the vertical sewing-machine bill motions. A number of lesser yellowlegs are in slightly deeper water. On the mudflats are many killdeers, a couple spotted sandpipers and a solitary sandpiper. Between mudflats and the very shallowest water, several peeps (appear to be mainly least sandpipers).

The killdeer nest mentioned on April 18, 2009.

18AP09. Killdeer incubating a nest in mulch around a tree in the picnic area, Tri-County State Park.

Ready and Waiting

by Carl Strang

The parking lot marsh at Mayslake Forest Preserve holds many muskrat mound houses this winter.

Two large mounds are plainly visible in the north end.

In each of the past two breeding seasons the only Canada goose nest on the preserve has been on a muskrat mound in this marsh. Thanks to presence and absence of leg bands, I know that it has been a different pair each year. Both nests were successful. Three seasons ago the muskrats had only bank dens, the water was shallower, a pair of geese nested on a low, exposed island, and the preserve’s pair of coyotes waded out and killed the incubating female and got her eggs.

Here are 3 more mounds in the center of the marsh.

With so many potential platforms this year, there is the possibility that more than one pair will nest there.

Add one more in the south end.

It’s not a big marsh, though, and an aggressive pair of geese may be able to keep others out. I’ll be interested in seeing what develops.

For the moment, Canada geese still are in their winter pattern. I have not followed them as closely this winter as in past years, but clearly more roosts have stayed active and more birds have hung around in this milder season. I checked out the Blackwell roost earlier this week, and found that though the geese continue to use it, the water has been drawn down.

Most of the roost area is in mudflats.

This is not simply the result of low precipitation.

The gate has been removed from the dam. There are plans to enlarge the zone of marsh-edge vegetation.

This could be a good place to see migrant shorebirds later in the spring.

Wool Grass in Winter

by Carl Strang

Sometimes winter botany is challenging, but not always. Last year I put some effort into learning to recognize the more common grasses, sedges and rushes at Mayslake Forest Preserve. On Friday I spent some time seeing what was still recognizable in late winter. Many were, to my eye, a matted uniform carpet of flattened brown leaf blades, but a few stood out. One of these was wool grass.

“Wool grass” is not in fact a grass, but one of the bulrushes.

Even the fruiting head retained much of its structure.

Some winter plants qualify as sculpture, as “found art.”

When I found this plant last summer, it impressed me.

For one thing, it towered above the other plants in its vicinity.

The flower heads were complex, and white mixed with green added interest.

You can see how the winter version in the above photo still reflects this structure.

I had hoped to do more winter plant photography this year, but the way it is going I will have to wait for another, snowier year.

Literature Review: Archean and Proterozoic

by Carl Strang

The Archean and Proterozoic Eons were immense periods of time in which the Earth cooled enough to form rocks and begin its Wilson Cycle of plate tectonic activity, the continents coming together and drifting apart in a Maypole Dance that goes on to this day. Life emerged from inorganic matter in the Archean, and achieved its first multicellular forms in the Proterozoic. We so often forget these eons in our rush to the Paleozoic, but research continues to fill the gaps in our knowledge and make more interesting these billions of years that constitute most of Earth’s (and life’s) history. Today I’ll share notes on some of the research that particularly struck me last year.

Chicken Islands, Georgian Bay. The Canadian Shield formed during the Proterozoic, but the plants and the glacier-rounded forms of the rocks tell how much has happened since.

S. Pizzarello, L. B. Williams, J. Lehman, G. P. Holland, J. L. Yarger. Abundant ammonia in primitive asteroids and the case for a possible exobiology. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1014961108     One problem in understanding the origin of life is the contradiction between the need for quantities of reduced nitrogen (e.g., ammonia) and evidence that the early atmosphere was neutral rather than reducing in its chemical activity. This group found that ammonia is carried in high concentrations to Earth within asteroidal meteorites, and this is a potential source of the material.

Anand Bala Subramaniam, Jiandi Wan, Arvind Gopinath, Howard A. Stone. Semi-permeable vesicles composed of natural clay. Soft Matter, 2011; DOI: 10.1039/C0SM01354D     They have mapped out some plausible steps for early cell formation. Montmorillonite clay, an abundant mineral, spontaneously can form spherical vesicles around air bubbles in water. The vesicles hold their structure as fluids and organics flow in through semipermeable pores in the vesicles and the air bubbles dissolve. Montmorillonite is known to act as a catalyst for the assembly of lipid membranes and RNA strands.

Shirey, Steven B., and Stephen H. Richardson. 2011. Start of the Wilson cycle at 3 Ga shown by diamonds from subcontinental mantle. Science 333:434-436. The mineral composition of inclusions within diamonds of different ages points to plate tectonics starting up 3 billion years ago. They argue that claims for earlier recycling of crust into the mantle need to be revised.

Lawrence A. David, Eric J. Alm. Rapid evolutionary innovation during an Archaean genetic expansion. Nature, 2010; DOI: 10.1038/nature09649     As described in a ScienceDaily article. They looked at the genomes of present-day organisms to trace innovative genetic events of the past. Their results indicate an event they call the Archean Explosion, a time 3.3-2.8 billion years ago when 27% of present-day gene families first appeared. The genes involved are mainly connected to electron transport in membranes, associated with oxygenic photosynthesis and respiration. Genes directly associated with the utilization of oxygen appear at the end of that period, connecting to geological evidence for the accumulation of oxygen in the atmosphere (the “Great Oxidation Event” of 2.5 billion years ago). This must have been a disastrous time for life, the oxygen leading to the death of then-dominant anaerobic forms. The researchers are hopeful that continued study can lead to the uncovering of still earlier genetic steps in the evolution of life.

T. Bosak, D.J.G. Lahr, S.B. Pruss, F.A. Macdonald, L. Dalton, E. Matys. Agglutinated tests in post-Sturtian cap carbonates of Namibia and Mongolia. Earth and Planetary Science Letters, 14 June 2011 DOI: 10.1016/j.epsl.2011.05.030     As described in ScienceDaily. The Snowball Earth glaciation was actually two separate periods when glaciers were pole to pole or nearly so, at 710 and 635 million years ago. This paper describes fossil shells, the first known, of microorganisms, possibly early shelled amebae, that lived soon after the first of these glacial episodes.

Biotechnology and Biological Sciences Research Council (2010, December 18). Rise in oxygen drove evolution of animal life 550 million years ago. ScienceDaily. Retrieved December 20, 2010, from http://www.sciencedaily.com­ /releases/2010/12/101217145647.htm     While describing research connecting oxygen detection mechanisms in humans with those in the simplest animal (Trichoplax adhaerens), the article points out that the rise of multicellular life 550 million years ago (late Proterozoic) coincides with an abrupt rise in atmospheric oxygen from 3% to 21%. Body size correlates with oxygen availability in multicellular animals.

Lessons from Travels: Big Trees

by Carl Strang

Northeast Illinois would have been intrinsically forested under recent climatic conditions, but was mainly prairie because fire prevented the forest from manifesting itself until European-Americans moved in and stopped it. Until then trees grew in fire shadows, small areas where wetlands or topographic breaks blocked fires pushed by the prevailing westerlies. A few of our trees, notably oaks and cottonwoods, reach sizes that arguably can be called “large,” but to appreciate how big trees (and therefore living things) can get, we need to travel. In North America, that means California. I haven’t experienced giant sequoias yet, but I found the coastal redwoods to be plenty impressive on a brief conference trip out there a few years ago.

Right away, as you pull into the parking lot at Muir Woods, just north of San Francisco, you get a sense of eye-popping bigness.

The trail there was quiet, I would have to say “hushed,” despite the presence of plenty of people. In part that no doubt was because of inspired awe, but the structure of the place absorbed sounds efficiently.

There was, however, a sense of spaciousness among the large trees.

The place didn’t seem hugely diverse, but as in the tropics some of that diversity was in the form of epiphyte communities.

Epiphytes are plants that live on another plant, not as parasites but using their host as a platform that elevates them into the light.

There is no shame in being the rube who gawks upward in such a place.

They are really really tall.

The biggest of them are amazing in their girth as well.

This perhaps gives the best sense of how huge these things really are.

Redwood forests can burn, though fire is not the frequent presence it was in Illinois. The trees have some resistance to it, and they also have the advantage of living in the coastal fog zone, much moister than northeast Illinois. Now we shift to Tasmania, to Mount Field National Park, to take a look at another big tree, the swamp gum.

Again, the diameter of these things impresses.

A rainforest climate again makes possible this kind of growth. And again, one plays the rube.

Swamp gums, the tallest hardwoods in the world, are very close to the coniferous redwoods’ height (more than 100 yards).

As with the whales I featured recently, the contrast in size provides perspective on our place. It encourages us to think about how large size is itself an adaptation that is advantageous in some environments or conditions, but size, whether large or small, results from a balance of selective factors that must fit a species into its community. Each organism succeeds in part because it is just the right size. It is somewhat mind boggling to realize that every species always displays a range of sizes, selective factors constantly are pushing and pulling to influence what the right size for each species is at a given time, the species all are balancing against one another simultaneously, and size is only one of many such characteristics.

Raccoon Species Dossier

by Carl Strang

I am overdue to share one of my mammal dossiers. This one is relatively large. As always, the dossier is limited to my own experience. I established it in the mid-1980’s, and since have added dated notes.

Raccoon

Raccoon, Aransas NWR picnic area, Texas

Raccoons occur in a fairly wide range of habitats, though they usually live in areas with some trees and wetlands. They can be abundant in residential areas. Raccoons are nocturnal, spending the day in a hollow tree or a woodchuck burrow (alternatively, in shed, attic, or chimney). They are active all year round, though somewhat less so in winter. They avoid activity in storms or extremely cold temperatures. Sometimes they sun themselves on a branch in summer. Centers of foraging activity are garbage cans in residential areas, and ponds, streams or marshes elsewhere. Their diet is extremely broad, but features small aquatic invertebrates and vertebrates (crayfish especially favored), also fruits and insects from terrestrial areas.

Females have 1 litter of young per year, born mostly in April or early May in northeast Illinois. Young remain in the nest several weeks, then begin following the mother (father doesn’t participate in rearing). Separation begins around September. Young often remain together in 2’s or more through their first winter. The young are especially vocal, uttering a rolling chatter when interacting with one another, giving loud cries when picked up, and occasionally giving a distinctive rising whimper which may be a call for mother. In play, young bounce around with shoulders humped above stiff front legs and hair raised. This probably leads into an aggressive display of adulthood.

21DE86. A well-established trail leads from a bur oak den tree for 20m, then splits 3 ways into fainter paths. All sets of tracks visible on that trunk led away from the den tree.

Raccoons, creatures of habit with a heavy walk on flat feet, produce clear trails in winter.

15JA87. Raccoon tracks in Willowbrook Back 40 are the first sign of that species I have seen on several preserves since heavy snow fell almost a week ago. This one seemed to be trying to minimize contact with the snow by walking on logs, walking on melted patches, and bounding in open stretches where deeper snow couldn’t be avoided.

20JA87. No raccoon signs in 3 days since new snow.

9FE87. Raccoon were active in the center of the Willowbrook Back 40 last night.

3JE87. A raccoon gnawed on a rabbit hind foot in brush near the great horned owl nest, Willowbrook Forest Preserve, at mid-day. It ran off quietly as I passed, at a fast diagonal walk or a trot.

22AU87. Photo and sketch of raccoon gallop, lope. 15 inches up to next set, 16.5 inches back to previous set, which was 14 x 5.5″ and looked a little more gallop-like. The set before that (19 inches back) was a gallop, borderline bound.

Sketch of raccoon gallop

Sketch of raccoon lope

14NO87. A raccoon was dying of distemper at Winfield Mounds Forest Preserve. It was on its back, eyes crusted shut.

Canine distemper is one of the most important causes of death in northeast Illinois raccoons.

10DE87. Lots of fresh raccoon tracks are all over Willowbrook Back 40 trails, compared to only 1 fresh set of opossum tracks.

23DE87. There has been some raccoon activity in recent nights, and much opossum activity.

16JA88. Considerable raccoon action last night, which was warm. No opossum tracks.

20JA88. Lots of raccoon and opossum activity last 2 warm nights, Willowbrook. The stream was high, no crossings observed.

The flat-footed, 5-fingered raccoon footprint is distinctive.

17MY88. A raccoon was resting, perhaps sleeping, on an exposed horizontal branch near the top of a big willow, at midday.

12OC88. A raccoon was out at midday, Willowbrook Back 40 (I made several daytime observations of this animal in the rest of this month).

19DE88. 2 raccoons but no opossums were active the last 2 nights around the Back 40 Nature Trail.

Raccoons normally walk in the pace gait.

9MR89. Despite increased warmth over past 2 nights, there has been no use of trails by raccoons.

2AP89. Photos of 2 raccoons asleep in the 29-inch pin oak near the NE corner of Cactus Camp, near Hartz Lake, in Indiana. I saw the one in the hole first, didn’t see the other (in the crotch of a fork just above hole) until I looked with binoculars.

The raccoons described on April 2, 1989. These probably were siblings from the previous year, not yet breeding.

13MY89. 2 raccoons in the same sleeping places as on 2AP.

10JE90. Warrenville Grove Forest Preserve. A raccoon was active in the woods not far from the river (though at least 30 yards from it), half an hour after sunrise, foraging among Solomon’s plume in the forest. When I, standing still 15 yards away, shifted, it jumped onto a tree trunk, but I kept still in my camo sweatshirt and the raccoon resumed its foraging. Later I looked at the area. The vegetation was stepped on and disrupted, with common 2-3-inch holes, scrapes.

26JA92. Hidden Lake Forest Preserve. Raccoons were active last night (fresh snow yesterday, overnight low around 20F). I found a raccoon inside a hollow oak, at ground level, sheltered by the overhang of the leaning trunk. It looked back at me, but did nothing more.

JE99. Tracks seen at Horsethief Canyon, central Kansas.

19JA99. Willowbrook. Raccoons came out for the first time since the major snowstorm of 2JA, sometime between the 15th and today.

26JA00. In spite of the very cold previous night (subzero F), raccoons were out, at least 2 individuals moving together. This winter a group of raccoons is moving back and forth between a den high up in a dead willow near the Willowbrook bridge, and a den along the nature trail in a smaller dying willow. On the coldest nights they tend not to use the bridge willow den, which is higher up and has a larger hole which goes practically down to the bottom of the den. The trail willow den has a smaller hole, is not so exposed, and at least one animal can fit below the bottom edge of the hole. On the warmer nights, though, they seem to prefer the more spacious bridge willow den.

Raccoon skeleton. Raccoon and deer bones are the ones most frequently encountered in the field.

31JA00. A raccoon was out last night in the newly added 6 inches of snow, gait in the deep snow entirely a diagonal walk for a long distance.

4MR00. Hemlock Hill, Morton Arboretum. After a night that dropped into the 20’s, a raccoon slept in the open crotch of a large red oak, 10 feet off the ground. Now sunny, 30’s.

1AP00. While running on the Prairie Path between Butterfield and Kirk Roads, I spotted a raccoon sleeping on a large, open branch of an oak in a small wooded area beside the trail. A warm, sunny day.

30AP00. Raccoon snoozing in a dead tree trunk, largely hidden in a rotted out cavity 12 feet up and only about 20 feet from the busy main trail at Waterfall Glen (section parallel to S railroad tracks).

The raccoon skull is distinctive in its size, rounded form, and mix of canine and flattened molar teeth.

9AU00. Last night at 3am, loud cries eventually got me out of a deep sleep. Going to the window I saw a raccoon below, uttering the last of the cries. They were loud, and different from other raccoon vocalizations I have heard. The sound was sniffing or snorting, even whinnying in quality but very high pitched and sounding like a conflict or fear-driven vocalization.

28DE00. At 1:30 p.m., a raccoon was eating snow from the large upper limbs of the big, largely dead tree 40‑50 yards NNE of the Willowbrook office building (visible from the north office window). It then turned around and climbed down into the large crack on the SE corner of the trunk. This marks the 4th confirmed den on the preserve, and the 3rd winter den (the hollow catalpa behind the opossum cage in the outdoor animal exhibit is known only to have been used by a female to keep her tiny cubs in spring of this year). The deep snow that fell in mid-December has kept raccoons in their dens for more than 2 weeks.

Raccoons create communal toilets, often on elevated tree branches. This one, at the base of several joined tree trunks, shows a heavy recent diet of mulberries by the local raccoons.

13JA01. At 10:30 a.m., a large raccoon was walking a deer trail near the place where the regional trail crosses the back marsh at Herrick Lake. It seemed perfectly healthy. After a short time it left the deer trail and, with some effort, forged its own path through the still-deep snow.

26AP01. Sounds of baby raccoons coming from the same catalpa as last year at Willowbrook. (Last year she moved the 2 young to another tree when they were old enough to walk; this one has a very small entrance).

Older youngsters peek out from their den.

19MY01. A large raccoon was well exposed on the open branches of a dying oak at the Arboretum, grooming itself at 9 a.m.

21MR02. A raccoon shifted into a diagonal walk on a wet-snow hillside. Better traction? No overlap-separation between the tracks of each side. Elsewhere in flat areas, it used the pace gait.

14AP02. A female raccoon carrying a baby smaller than her head, more than 250 yards along the edge of the east side of Lake Maxinkuckee (Indiana), between 2:30 and 3:00 p.m.

2012. My notes since 2002 have been logged mainly in my natural history survey records at Willowbrook, Fullersburg and Mayslake. At Willowbrook it seemed that every year a female had her litter in a smaller den (warmer? more secure from males?), and at some point shifted them to a larger more open one. At Fullersburg I was impressed by the raccoons’ willingness to go out on very cold nights that elsewhere usually would keep them in. Even on single digit (F) nights, they routinely swam across Salt Creek rather than going the long way and taking a bridge. I started this blog at the same time my office shifted to Mayslake, and any significant observations from November 2008 on could be found by searching on “raccoon.”

Literature Review: Hadean Update

by Carl Strang

Last year’s winter series was a review of the prehistoric life and geological history of northeast Illinois (if you are interested, access it through “Prehistoric Life series” under “Categories” in the left sidebar). Paleontology as a field of research has the advantage that it is covering billions of years of time, and so there is always much to learn each year from newly published findings. The remainder of this season’s reviews of last year’s literature will focus on this subject. It makes sense to go chronologically, so I’ll begin with the Hadean Eon, the time when Earth formed but before it cooled enough for the first rocks to crystallize that have survived to the present day.

Moon over Georgian Bay

Bottke, William F., et al. Stochastic Late Accretion to Earth, the Moon, and Mars. Science, 10 December 2010: 1527-1530 DOI: 10.1126/science.1196874     They studied the composition of mantle-derived rocks on Earth, Moon and Mars to test the degree to which these bodies were struck by large impactor bodies after their basic structures were established. Such bodies weren’t so large that they completely restructured the planets (as did Theia on Earth), and so their contents became added to the more surface portions rather than the cores. In particular the presence of “siderophile” metals (gold, platinum, palladium, osmium and iridium for example) is indicative of such impacts, and would not be present in the usable amounts we see on Earth without such additions. The time frame is a few tens of millions of years after the Theia impact. The largest of these hitting Earth is estimated to have been the size of Pluto, 1500-2000 miles in diameter. It may be responsible for as much as a 10° adjustment of the Earth’s tilt from its previous orientation. The largest Moon impactors are estimated in the 150-200 mile diameter range, and are the likely source of water there.

Kerr, Richard A. 2011. Planetary two-step reshaped solar system, saved Earth? Science 332:1255. This news article described a new model, published in Nature, of planetary dynamics in the developing Solar System. The model, which focuses on gravitational interactions of the sun, developing planets, planetesimals and gases explains today’s endpoint better than earlier ones, and answers a lot of puzzles. Earlier work suggested that Jupiter should have swept in close enough to the Sun to wipe out the inner planets, including the Earth. This model shows that Jupiter came to within 1.5 Earth orbits of the sun, but then was drawn back out by a combination of factors, particularly the draw of Saturn. That close approach kept Mars small, as Jupiter limited the planetesimals available to the fourth planet. The model also accounts well for the asteroid belt and aspects of its structure (mainly dry, rocky asteroids inward and others rich in ice and organic compounds dominating the outer belt). All of this happened over a relatively brief period of 5 million years, 4.6 billion years ago.

Dustin Trail, E. Bruce Watson, Nicholas D. Tailby. The oxidation state of Hadean magmas and implications for early Earth’s atmosphere. Nature, 2011; 480 (7375): 79 DOI: 10.1038/nature10655     As described in a ScienceDaily article. They looked at the oxidation state of elements in zircon minerals from the earliest rocks, and found that these indicate an early atmosphere high in oxygen-containing gases such as carbon dioxide, water and sulfur dioxide (though not, of course, free oxygen). This contradicts the current understanding that the early atmosphere (in which life arose) was a reducing atmosphere with ammonia, methane, carbon monoxide and hydrogen sulfide as dominant gases.

« Older entries

%d bloggers like this: