Crowlspace

In science there’s always a second opinion - some better informed than others. I can’t fault anything that John Hawks, anthropologist, has to say on his speciality, so check out his corrective to the claim humans went through a bottleneck some 70,000 years ago…

Sub-Saharan Population Size

…basically some questionable assumptions have to be made to produce the proposed bottleneck at 70,000 bp. As John explains somebody hasn’t done their maths or the science media has jumped on ambiguous statements without checking a bit harder. The bottleneck can be produced by a higher mutation rate, but it would have to turn-off before the move Out-of-Africa, some 60,000 years ago, else some weird results would arise (like American Indians originating 7,000 years ago, not 14,000, or modern Asian/Australasian groups appearing 30,000 years ago, some 20,000 years too late for the Australian Aborigines.)

Assumptions about populations and isolation between them might change the picture, so only better data can bring that time period into more definite focus.

Human beings are a lucky species and just how lucky is coming clear through population genetic analyses. One scary finding is the confirmation of a population “bottleneck” - we were reduced in numbers to a mere 2,000 people some 70,000 years ago (70 kya.) Our species had a common female ancestor ~200 kya (traced by mitochondrial DNA) and a common male ancestor ~100 kya (traced by Y-chromosomal genes), and in the time since “Eve” we broke apart into small groups and remerged just prior to the bottleneck according to this recent news report.

Consider the fate of our near kin:

and ponder just how lucky we were.

POST SCRIPTUM the original research the news bite was based on is available online at the American Journal of Human Genetics here: The Dawn of Human Matrilineal Diversity

Humans are bipedal apes. Yet we find that rather odd because our ape kin aren’t usually bipedal on the ground. Did we get bipedal on the ground too, or did some other environment suit that peculiar locomotive style better? A sextet of pictures from a Public Library of Science article….

Gorilla female plucks a stick from a swamp floor

…which evokes so many resonances for me. Look at how she walks clutching that stick.

At the other end of our journey, as a species, is the prospect of Interstellar Migration. The Ultimate Project is a plausible plan for an Interstellar colonization mission, but of World-Ship proportions. The basic plan is for a vast million-person “Star City” to traverse 20 light years at 0.002c (600 km/s) on a ten millennial journey to a new star system for humanity. For propulsion the Star City will use immense D-He3 fusion rockets, taking a century or so to build up speed.

Such fusion drives have exhaust velocities of ~ 15,000 km/s, so I wonder why the Star City isn’t going faster? To avoid interstellar debris, which is pretty lethal at speeds over ~ 0.01c, and to spend as much time between the stars as seems reasonable, I suspect. Such a Star City would allow for incredible astronomical collaborations between it and our Solar System, for example measuring the nearby Galaxies with stunning precision - imagine parallaxes out to the Virgo Super-Cluster. Thus why I call it “Star City” as it seems more like a mobile Observatory than a colonizing mission.

Read more, check it out, and best of all any contribution you make now will, possibly, shape events 500 years from now when the Project launches.

With the New Horizons probe rushing to Pluto, this is a good time to ponder just what we might find. Spectroscopes have told us that Pluto has a wispy methane atmosphere, probably with a dash of nitrogen thrown in - but just how much? Pluto has undergone quite a few occultations - passages in front of distant stars, which causes Pluto’s shadow to pass our way every few years. This technique has told us how big Pluto’s largest moon, Charon, is i.e. about 606 km in radius. But Pluto’s atmosphere refracts the starlight and so we can’t directly measure Pluto’s shadow, merely the shadow of his atmosphere and surface combined.

What might be possible within the bounds of current data? Here’s a study from MIT’s Planetary Astronomy Laboratory…

Changes in Pluto’s Atmosphere: 1988-2006

…a couple of possibilities might be encountered by New Horizons in 2015. Firstly a cold surface at ~35 K with 3.3 microbar of 99% N2 atmosphere - this means a solid radius for Pluto at about ~ 1168 km. Or a hazy troposphere and a surface at 1120 km radius, 43 K and 310 microbar of 99% N2. Both are cold, but the last means more gas, warmer surface and less crustal ices. If the crust is frozen N2/CH4 coated water-ice (density ~ 0.94 at those temperatures), then it might be about 114 km thick over a core of muddy silicates (density ~ 2.7.) Assuming the radioactive isotope levels seen in chondritic rock (i.e. stony meteorites) the global heat flow is ~100 GW. This is not quite enough to produce liquid water beneath the icy crust unless the frozen surface gases slow down conduction, or the liquid isn’t water. A eutectic mix of ammonia/water freezes at 176 K, while a eutectic mix of sulfuric acid/water melts at 211 K. Both sound nasty, but they’re conceivable media for some kind of biochemistry.

But a pure ice Ih crust is unlikely on Pluto - it’s more likely to be, at least partly, methane clathrate, with a much lower conductivity (0.4 W/mK vs 7 W/mK for H2O at 95 K) and thus an ocean might be feasible if there’s enough heat from Pluto’s core. Will it be water? Cloudy ammonia? Dilute acid? Or ammonium sulfate in solution? According to a study by Dominic Fortes and colleagues ( Ammonium sulfate on Titan: Possible origin and role in cryovolcanism, Icarus 188 (2007) 139–153 ) the ammonium sulfate should allow rapid transport of clathrate towards the surface and quite explosive volcanism should result as the clathrate decomposes with a large release of pressurised gas.

So will we see splashes of ammonium sulfate across the surface of Pluto? And will New Horizons detect it? Perhaps… and in doing so we might get a glimpse of Titan’s own cryovolcanic processes too.

Uber science-writer Carl Zimmer muses on some utterly fascinating research on rewiring E.coli’s gene networks…

The More We Know About Genes, the Less We Understand

In the latest issue of Nature, scientists reported an experiment in which they wreaked havoc with E. coli’s network. They randomly added new links between the transcription factors at the top of the microbe’s hierarchy. Now a transcription factor could turn on another one that it never had before. The scientists randomly rewired the network in 598 different ways and then stepped back to see what happened to the bacteria.

You might expect that they all died. After all, if you were to pop open the back of an iPod and start linking its components together in random ways, you’d expect it to crash. But that’s not what happened.

About 95 percent of the rewired bacteria did just fine with their new networks. They went on with their lives, feeding, growing and dividing. Some even performed better than microbes with the original wiring, under some conditions.

…which is an incredible result. Carl muses there’s “something about gene networks” - gene networks being the program that controls an organism’s DNA activities - which lets them handle massive perturbations like a total rewiring. The puzzle is profound, but it indicates a great truth in biology - the whole, the organism, is greater than the sum of its parts, the genes, proteins and so forth that make it. They work together in a harmony that may have a higher-level abstract structure that allows great stability.

Here’s the Nature paper in abstract… Evolvability and hierarchy in rewired bacterial gene networks Ref: Nature 452, 840-845 (17 April 2008) | doi:10.1038/nature06847

…and it’s truly an amazing result. But just what does it mean? I think it means that genetic mutation - via gene changes or changes to regulator sequences - is just one step in the process leading from genome to living thing. The whole of an organism acts as an “editor” that decides if a DNA change makes sense - that’s the first level of “natural selection” and it seems a lot more able than the old “random mechanism” view that treated cells as intricate clockwork. Instead the cellular system is much more responsive and dynamic in a way we have trouble grasping because so much collective molecular behaviour is involved.

At the edge of our Solar System is a Belt of small ice-worlds - the well-known Pluto and Charon, the unofficial Tenth Planet, Eris, and several other largish objects that the media doesn’t say much about. One of the latter is 2003 EL61, which is yet to get a real name, as the discovery code-name makes clear. It’s roughly Pluto-sized, but flattened into a football shape due to a very high rotation rate. It’s also much denser than its fellow ice-worlds, which led its discoverers to conclude it had formed in a violent collision with another ice-world. Supporting that theory are small objects in the Belt that have the same spectroscopic colour as 2003 EL61. In the Main Belt of asteroids that ALWAYS means the objects are related - for example, we have pieces of the asteroid Vesta that came to Earth as meteorites so we could check.

Computer simulations of the big smash-up support the idea, but there seemed to be no way of dating just when it occurred - bar one. Ice mixed with methane changes colour over millions of years as the methane is broken down by cosmic-rays and its break-down products recombine as “tholins” - pinkish organic material. Older ice-worlds in the Belt show these colours, indicating their icy crust once contained methane and now is diluted with a layer of tholins.

BUT 2003 EL61, and the orbitting bits of it, don’t show those tholin colours….

The Youthful Appearance of the 2003 EL61 Collisional Family

…which basically concludes that the whole group of parent body and fragments either have an anomalously low level of methane or their collision occurred less than 100 million years ago. Either conclusion is quite startling, as ice-worlds everywhere else in the Belt seem to have methane. Either the smash-up was so violent and hot that all the methane was driven off - but why didn’t the water explode as a great cloud of steam? Or the methane is there and the smash-up occurred, at the earliest, in the days of the dinosaurs. In which case a rogue dwarf-planet careened through the Belt in what is “recent time” for big planetary collisions.

Here in Oz I’ve vague ideas as to who Ben Stein is, but I can only smell bullshit with his current doco. Here’s a web-site that reveals the truth and exposes the lies…

Expelled Exposed

…read it, be educated and get really pissed off at the self-righteousness that poses as Judaism/Christianity. If people want to claim to be believers in the Truth, then they should get informed and stop spouting old bullshit. God’s bigger and better than such garbage, and it’s time people believed Him with integrity.

Young Earth Creationism is a belief in Biblical Inerrancy inspired delusion, nothing more, as it has no real evidence in its favour, bar a very particular school of interpretation of the Bible. And now we have direct proof that the world is more than a mere 6,000 years old…

World’s oldest living tree discovered in Sweden

The world’s oldest recorded tree is a 9,550 year old spruce in the Dalarna province of Sweden.

The spruce tree has shown to be a tenacious survivor that has endured by growing between erect trees and smaller bushes in pace with the dramatic climate changes over time.

For many years the spruce tree has been regarded as a relative newcomer in the Swedish mountain region.

”Our results have shown the complete opposite, that the spruce is one of the oldest known trees in the mountain range,” says Leif Kullman, Professor of Physical Geography at Umeå University.

A fascinating discovery was made under the crown of a spruce in Fulu Mountain in Dalarna. Scientists found four “generations” of spruce remains in the form of cones and wood produced from the highest grounds.

The discovery showed trees of 375, 5,660, 9,000 and 9,550 years old and everything displayed clear signs that they have the same genetic makeup as the trees above them. Since spruce trees can multiply with root penetrating braches, they can produce exact copies, or clones.

The tree now growing above the finding place and the wood pieces dating 9,550 years have the same genetic material. The actual has been tested by carbon-14 dating at a laboratory in Miami, Florida, USA.

…thus any global Flood of Noah dates to before c.7,550 BC, at the very latest. So either Noah’s Flood wasn’t global, or else it was a lot further back in time than a narrow reading of the Bible allows. Of course for a lot of Fundamentalists there is no great drama in a Flood long, long ago. A geophysicist friend of mine, Glenn Morton, believes the Bible and based on his geological knowledge places the Flood at the Messinian - c. 5.5 million BC.

In the early 1970s John Lewis modelled the interiors of the outer planet satellites and discovered they might have sub-surface oceans of ammonia/water…

Lewis, J.S. (1971) Science, Volume 172, Issue 3988, pp. 1127-1128

Lewis, J.S. Icarus, Volume 15, Issue 2, October 1971, Pages 174-185

Abstract
Steady-state thermal models for the icy satellites are constructed in which the energy released by radioactive decay in the interiors of the satellites is exactly balanced by the net radiative loss from their surfaces. It is shown that the Galilean satellites of Jupiter and the larger satellites of Saturn, Uranus, and Neptune very likely have extensively melted interiors, and most probably contain a core of hydrous silicates, an extensive mantle of ammonia-rich liquid water, and a relatively thin crust of ices. Consequences of this model relating to the Galilean satellites and the rings of Saturn are briefly described.

The atmospheric compositions and densities of the large icy satellites and certain features of the retention of volatiles during accretion are discussed.

Thus we’ve known about these dark, inner Oceans for over 3 decades or so. Opinion, in science, is never constant without data, and some estimates of the heat-transfer via solid-state convection of ice has meant the liquid interior models have fallen out of favour - at least until more data for the oceans came to hand from Galileo and Cassini. Galileo discovered that Ganymede, Callisto and Io had detectable magnetic fields - the case of Callisto, the field seemed localised to a thin layer of salt-containing fluid just under the outer ice, enwrapping the ‘mud’ mantle below. Cassini has discovered that Titan’s outer crust is decoupled from the inner layers, probably because of a liquid mantle of ammonia/water or ammonium sulfate.

But what about other moons? Europa very probably has an ocean as its crust looks like Arctic sea-ice, and Enceladus’s geysers are hard to explain via any other cause. Further afield? Here’s an interesting paper from Paul Schenk and Kevin Zahnle…

Schenk & Zahnle, Icarus, Volume 192, Issue 1, 1 December 2007, Pages 135-149

Abstract
New mapping reveals 100 probable impact craters on Triton wider than 5 km diameter. All of the probable craters are within 90° of the apex of Triton’s orbital motion (i.e., all are on the leading hemisphere) and have a cosine density distribution with respect to the apex. This spatial distribution is difficult to reconcile with a heliocentric (Sun-orbiting) source of impactors, be it ecliptic comets, the Kuiper Belt, the scattered disk, or tidally-disrupted temporary satellites in the style of Shoemaker–Levy 9, but it is consistent with head-on collisions, as would be produced if a prograde population of planetocentric (Neptune-orbiting) debris were swept up by retrograde Triton. Plausible sources include ejecta from impact on or disruption of inner/outer moons of Neptune. If Triton’s small craters are mostly of planetocentric origin, Triton offers no evidence for or against the existence of small comets in the Kuiper Belt, and New Horizons observations of Pluto must fill this role. The possibility that the distribution of impact craters is an artifact caused by difficulty in identifying impact craters on the cantaloupe terrain is considered and rejected. The possibility that capricious resurfacing has mimicked the effect of head-on collisions is considered and shown to be unlikely given current geologic constraints, and is no more probable than planetocentrogenesis. The estimated cratering rate on Triton by ecliptic comets is used to put an upper limit of 50 Myr on the age of the more heavily cratered terrains, and of 6 Myr for the Neptune-facing cantaloupe terrain. If the vast majority of cratering is by planetocentric debris, as we propose, then the surface everywhere is probably less than 10 Myr old. Although the uncertainty in these cratering ages is at least a factor ten, it seems likely that Triton’s is among the youngest surfaces in the Solar System, a candidate ocean moon, and an important target for future exploration.

…which seems to indicate a very dramatic thermal history for Triton, with a more global melting of its crust than the apparently localised melt on Enceladus’s south pole. If so, then the sub-surface ocean is potentially very close to the surface and liable to burst through in cryovolcanic events, making the moon a very interesting target for future investigation.

A new super-Earth has been announced around M-dwarf Gliese 436…

Scientists Find Smallest Exoplanet

…now the radius quoted is ~ 1.5 Earth radii. Different mixes of silicates and iron give slightly different indexes (0.272-0.268) for a power-law fit to the mass-radius curve - in this case lets take the average ~0.27, which means the planet is ~ 1.544 Earth radii. Seems the media was listening, which is unusual for a space-science story. Surface gravity would be 2.1 gee so it’s not a long-term habitable planet, but alright for visits in exoskeletons. Just 30 light-years away, so a laser-sail could reach it in ~ 100 years at 0.3 c.

Could humans get there? Another recent news item is further results from earlier studies on H2S gas induced suspended animation (SA) in mice… Rotten egg gas to Save Mars Mission …though that item doesn’t discuss further possibilities of inducing the effect via its metabolites so there’s no direct poisoning via the hydrogen sulphide itself. The research is still too basic to say what the effect on humans will be. Mice are a good start.

Let’s imagine - say the SA effect is like time-slowdown that some writers have imagined. What would that imply? Perhaps a crew could be augmented by smart AI that responds to circumstances faster than the ~ 100-fold slower crew. And what would 1 subjective year be like in induced torpor? Could muscles be used at all, or would that be too fast? Imagine crew in power-chairs controlled purely by (very slow) thoughts, with robotic arms. A normal speed person would be witness to some very strange effects, and would be a blurry figure to a time-slow crew person.

Would you go, if you could? Or some place closer, like Alpha Centauri B’s putative rocky world? That would be at least 30 years round-trip at 0.3 c. Would you risk being cut-off from the rest of humanity for so long? Good telecommunications, via laser, would allow you to keep track, but you wouldn’t be able to contribute to it without a multiyear time-lag. Could you stand the separation? Could you tolerate the same faces nearby for +30 years?