Plate tectonics and Life
Posted by sibylle in Science of Dune (Saturday February 23, 2008 at 4:56 pm)

Guest post by Bruno Hache, chemist:

Dune: the possible . . .

2. Plate tectonics and life:
We find the following statements in Sibylle Hechtel blog in the section about her interview of the Second International Convention of the Mars Society:

Chris McKay, of NASA’s Ames Research Center as to whether life existed on Mars:
‘‘Early Mars, when it was thought to have life, was warmer and had liquid water on its surface. The planet lost its atmosphere and became much colder.’’

Diana Valencia of Harvard University also said:
“Plate tectonics are essential to life as we know it, our calculations show that bigger is better when it comes to the habitability of rocky planets.”

Hechtel also says:
‘‘Plate tectonics are crucial to a planet’s habitability because they enable complex chemistry and recycle substances like carbon dioxide, which acts as a thermostat and keeps Earth balmy. Carbon dioxide that was locked into rocks is released when those rocks melt, returning to the atmosphere from volcanoes and oceanic ridges.’’

Chris McKay (see above) also said:
‘‘One hypothesis is that carbon dioxide (CO2) is unstable and forms calcium carbonate (CaCO3).  On Earth, the subduction plates (plate tectonics) take CaCO3 into the interior where the core’s heat releases the CO2 - a prime “greenhouse” gas that helps retain heat - back to the atmosphere’’.

This mechanism for the recycling of CO2 by volcanic activity is explained in “some” details in the Surface Chemistry section:
http://en.wikipedia.org/wiki/Geology_of_Mars

“It is thought that Earth, being hotter, transported much of the iron downwards in the 1800 km deep, 3,200 °C (5,800 °F), lava seas of the early planet, while Mars, with a lower lava temperature of 2,200 °C (4,000 °F) was too cool for this to happen.[5]. While the possibility of carbonates on Mars has been of great interest to exobiologists and geochemists alike, there is little evidence for significant quantities of carbonate deposits on the surface. ”

Also found on the Geology of Mars in the Magnetic Field and Internal Structure – Tectonics section:
“As a result of 1999 observations of the magnetic fields on Mars by the Mars Global Surveyor spacecraft, it was proposed that during the first half billion years after Mars was formed, the mechanisms of plate tectonics may have been active, with the Northern Lowlands equivalent to an ocean basin on Earth. ”

This is supported in more details by the following report:
http://science.nasa.gov/newhome/headlines/ast29apr99_1.htm

Some measurements that have been recorded by the Magnetometer of the Mars Global Surveyor spacecraft in 1999 confirm the absence of a global magnetic field.  The key consequence of the lack of magnetic field is:
“… unlike on Earth, the implied plate tectonic activity on Mars is most likely extinct.”

Confused yet?

I was!  But it caught my attention big time and I was not satisfied with the above explanations and needed to learn more to satisfy my scientist curiosity.  Some important details were overlooked for the eye of the reader, especially for the scientifically-literate readers.  My intention here is to expand on some of those details and propose an additional mechanism on how a rocky planet with oceans can further recycle CO2 from CaCO3.

Bruno expands about Diana Valencia’s comments:
Size matters because smaller planets have a smaller crust that can act as an insulator.  The external crust on a planet like Mars, Venus or Earth is like an egg shell.  But internal pressures do develop underneath the crust that acts like a pressure cooker.  Once in a while, a breach in this crust will trigger a volcanic eruption.  Without this crust and without the extra heat of the bigger planets core, smaller planet will lose the heat of their core faster than bigger ones.  Once the core is no longer in the form of liquid metal, the loss of the magnetic field shut down the plate tectonics and concomitant volcanic activity (temperatures too close to 840 ˚C / 1544 ˚F), no more plate tectonics nor volcanic activity, no CO2 recycling, no Prime ‘‘Greenhouse’’ gas, not enough heat to keep water in a liquid form, no life is possible.

Hypothesis:
Is it also possible that the higher gravity will help retain the greenhouse gases?
I presume yes since the Giant planets such as Uranus and Neptune are quite gaseous in nature.
In http://en.wikipedia.org/wiki/Neptune#Physical_characteristics
“Neptune’s temperature at its cloud tops is usually close to _218 °C… The temperature in Neptune’s center is about 7,000 °C, which is comparable to the Sun’s surface and similar to most other known planets.”

Therefore, the size of those Giant planets is big enough to retain gases by simple gravity as implied by Helium rain on Jupiter:  Rain-like droplets of helium and neon precipitate downward through this layer…”  Also to consider, those planets being far away from the Sun, are so cold, that, some if not most of those gases are in fact  liquid in the upper atmosphere, which helps that those gases do not escape to Space!

For example of that gravity effect when considering a gas giant of our Solar System - Jupiter:  http://en.wikipedia.org/wiki/Jupiter#internal_structure
“The presence of the core is also suggested by models of planetary formation involving initial formation of a rocky or icy core that is massive enough to collect its bulk of hydrogen and helium from the protosolar nebula.  The core may in fact be absent, as gravitational measurements aren’t precise enough to rule that possibility out entirely. Assuming it does exist, it may also be shrinking, as convection currents of hot liquid metallic hydrogen mix with the molten core and carry its contents to higher levels in the planetary interior[22].”

McKay said above:  “…CO2 recycling… and CO2 is unstable…”
Bruno would like to clarify that statement from McKay.
Bruno says:  ‘‘In fact, CO2 is not unstable.  But it is rather more stable at life form temperature when it is in the form of CaCO3.  In turn, CaCO3 is unstable under high heat and when exposed to acids.’’

Let’s explore this hypothesis in more details with what we know about CaCO3 on Earth and having in mind Diana Valencia’s comments (above) about the size of planets and their life-form habitability.

An industrial process for the production of CaO routinely used by the chemical industry is called calcining.  It exploits exposing CaCO3 to high heat, at temperatures above 840 ˚C (above 1544 ˚F).  At this high temperature, the following chemical transformation happens and releases CO2:

CaCO3 + heat ‡ CaO + CO2 (g)

http://en.wikipedia.org/wiki/Calcium_carbonate

Since calcium carbonate is a more stable form of CO2 at life form temperatures, CaCO3 deposits constantly occur on Earth (Chalk, Limestone, and Marble).

On a planet with plate tectonics and volcanic activity, the heat of earthquakes and more specifically volcanic eruptions is sufficient to promote the above decomposition of CaCO3.

Mars having no plate tectonics and no volcanic activity as evidenced by the Mars Global Surveyor (above), CO2 cannot be recycled back in the atmosphere by the extreme heat of volcanic eruptions since plate tectonics have ceased to exist.

Acidic recycling of CO2 under volcanic eruptions:
This is another hypothesis I would like to POSTULATE on our comprehension on the plate tectonics and CO2 recycling.  In planets with large amounts of oceans, plate tectonics and concomitant volcanic activity like we know on Earth, all the ingredients are there for CO2 recycling by an acidic mechanism as well.  During a volcanic eruption, the ejection of SO2 is another one of the main gazes that is liberated besides CO2.  When a volcanic eruption happens in deep sea like the sulfur vents, there is tons of water near the sulfur vents.  This provides the ingredients necessary for the transformation of SO2 into H2SO4, sulfuric acid.

Carbonates in general also have another useful property (besides heat instability) in the context of volcanic activity and CO2 recycling.  Carbonates such as CaCO3 are unstable to acid.  Any volcano will eject tons of SO2, a chemical precursor to sulfuric acid, H2SO4 that we routinely get in acid rain for example.  Acid rain in the form of dissolved H2SO4 OR with surrounding water from a sulfur-vent in deep sea will dissolve CaCO3 into more water-soluble CaSO4 and release CO2 into the atmosphere:

H2SO4 (aq)+ CaCO3 ‡ CaSO4 (aq) + H2CO3 (carbonic acid)

Carbonic acid is unstable and decomposes/dissociates spontaneously in the following manner:

H2CO3 ‡ H2O + CO2 (g)

To recycle the CO2 from CaCO3, the heat of a volcano is required which is probably the main stream mechanism for CO2 release on rocky planets.

However, this acidic mechanism to release CO2 is probably a minor component compared to the spontaneous high heat decomposition of CaCO3.  This is especially true in early planets that do not yet have oceans, the ingredient necessary for the acidic mechanism to occur.  The kinetics of the heat decomposition is most likely higher than the kinetic of the acid decomposition.  The acid pathway simply needs water to react; there is not much water that will sustain temperatures above 840 °C (above 1544 ˚F)!  But in the Sulfur vents Sibylle Hechtel refers to about the cyanobacterias, both the heat and the acid mechanism probably compete very well; there is plenty of water at depths of 10000 m!

This heat decomposition mechanism that we know on Earth supports that the absence of plate tectonics and volcanic activity on Mars makes CO2 recycling simply not possible on Mars, resulting in the apparently cold, dead planet that we observe today.

The greenhouse effect of CO2:
CO2 is an important greenhouse gas because it reflects IR radiation back to the ground, hence the Global Warming we slowly observe on Earth since the beginning of the industrial revolution. CO2 absorbs in the IR.  Warm CO2 will release this heat back in all directions (3D) and most of that heat is lost to Space.

A portion of that released heat will be returned to the ground.
http://en.wikipedia.org/wiki/Greenhouse_effect

‘‘The molecular vibrations of CO2 (IR) return 5% of that heat back to the ground by [reflectance].  This heat retention eventually results in a temperature at which water is in a liquid form.  Water needs to be liquid so it can act as the universal solvent essential to life.  Water also has several IR wavelengths and will readily absorb heat.

In more details, H2O vapor reflects 36% of IR radiation; CO2 reflects 9% and O3 (ozone) only 3% of the IR radiation.  Water has as a high heat capacity and this heat retention of water is synergistic with CO2.  Both are believed to be essential to maintain temperature favorable for life on Earth.’’

Wikipedia also mentions:
‘‘The Earth’s average surface temperature of 15 ˚C (59 °C) is about 33 ˚C (59 °F) warmer than it would be without the greenhouse effect.’’

In summary, the existence of life on a planet is a succession of planetary scale events and requirements:
Bigger planets will be OR will stay warm enough to generate plate tectonics activity and concomitant volcanic eruptions.
If a planet is big enough, the planet will retain that core heat more efficiently.
Volcanic eruptions will liberate CO2 due to the plate tectonics on bigger planets.
CO2 helps to retain heat on the ground – the greenhouse gas warming effect.
With that heat, water is in a liquid form.
Water is essential to dissolve inorganic and more importantly organic molecules that are essential to life.

Based on those scientific observations and evidences presented in this document/short essay, if those planetary scale events and requirements are met, life as we know it on Earth can exist and flourish!

Bruno Haché
M. Sc. Chemistry
Large-Scale Chemist in the Pharmaceutical/Biotech industry

For comments or for questions, please click on the red number right of the title.

Science of Dune: Worms on Earth
Posted by sibylle in science writing, Science of Dune (Saturday January 26, 2008 at 9:44 pm)

worm.jpg

Bootlace worm - Lineus longissimus

Image: Steve Trewhella (published on the MarLIN Web site)

This animal is among the world’s longest. It may reach a length of more than 50 meters!

I’ve been discussing the fictional sandworm of Dune. So far, the data indicate that the planet Arrakis, or Dune, could exist, but that life could not have evolved on a planet in orbit around Canopus (where Herbert places Arrakis). Even if Dune were terraformed and introduced life existed there, it could not long flourish in the absence of plate tectonics.

Now let’s look at what types of worms exist on Earth, where we enjoy abundant water and oxygen, and plate tectonics regularly causes earthquakes and volcanoes that recycle our carbon dioxide (among other things).

The Bootlace Worm, Lineus longissimus, grows over 50 meters long! That’s over 150 feet, and while not quite reaching the proportions of Herbert’s sandworms, it comes pretty close!

This lowly animal won the title of World’s longest animal, when a specimen measuring 180 feet beat out the longest dinosaur and the Blue Whale.

Along the coast of Norway, scientists found 30-meter long individuals and estimate that they can reach 60 meters when they stretch their body to its full length.

So why can’t Dune’s sandworm be this big?

The Bootlace Worm lives in the ocean, with certain problems like nutrient exchange, water balance, excretion, and mobility taken care of since it’s immersed in water. A terrestrial animal faces numerous challenges, such as water balance and thermoregulation that marine organisms don’t have to deal with.

And then, Dune has no oceans and Herbert said that water is poisonous to the sandworm. So we won’t find Lineus longissimus or other animals like it on Dune.

worm1.jpg

worm2.jpg

Giant ribbon worm

Dune: the possible . . .
Posted by sibylle in science writing, Science of Dune (Wednesday January 23, 2008 at 8:53 am)

and the implausible, less possible, or improbable.

Let’s look again at how much of Frank Herbert’s Duniverse is realistically possible based on known science, and how much is highly unlikely (in terrestrial science).

1. Arrakis and indigenous life.

When Herbert wrote Dune, we did not yet have the ability to see or find other planets. We assumed they existed—after all, if our sun has a bunch of planets, why wouldn’t other stars have them also? But we had no observed data of other planetary systems. Now we’ve observed over 100 planets and are actively searching for more.

Herbert places Arrakis around Canopus, a yellowish-white supergiant star. Kevin Grazier, on pages 96 – 98 in the Science of Dune, puts the lifetime of supergiants at only a few hundred million years. He concludes that life (as we know it) couldn’t have evolved on Arrakis (life on Earth took 800 my) and that Arrakis would have been terraformed!
tect.jpg
Plate tectonics: Heat from the Earth’s interior drives plate tectonics. Credit: World Book illustration by Raymond Perlman and Steven Brayfield, Artisan-Chicago

2. Plate tectonics and life.

In 1999, I attended the Second International Convention of the Mars Society (see my article) and interviewed Chris McKay, of NASA’s Ames Research Center as to whether life existed on Mars.

Early Mars, when some scientists think it could have had life, was warmer and had liquid water on its surface. The planet lost its atmosphere and became much colder. One hypothesis is that carbon dioxide (CO2) is unstable and forms calcium carbonate (CaCO3). On Earth, the subduction plates (plate tectonics) take CaCO3 into the interior where the core’s heat releases the CO2 - a “greenhouse” gas that helps retain heat - back into the atmosphere.

Mars has no plate tectonics and no CO2 recycling occurs. The binding of atmospheric CO2 into CaCO3 may have led to the loss of Mars’ atmosphere and its consequent transformation into a cold, dry, dead planet. When I interviewed McKay he did not think that planets without plate tectonics would long sustain life. Astrobiology Magazine discusses the role of plate tectonics in maintaining Earth’s climate and the nature and distribution of habitable environments in the Universe.
If Dune has no plate tectonics, this could make the persistence of (terrestrial-type) life less likely.

Diana Valencia of Harvard University said, “Plate tectonics are essential to life as we know it.”

Dune: science versus fiction
Posted by sibylle in Science of Dune (Thursday January 17, 2008 at 8:39 pm)

scienceofdune.jpg

I want to explain and clarify several points in my essay, ‘The Biology of the Sandworm’ in The Science of Dune. When possible, I will include pictures or diagrams in coming posts.

Scientific method

I made some basic assumptions in my essay, which I list below. When I use the term ‘assumptions’, I’m using this term in the mathematical or scientific sense of ‘postulate’ or ‘hypothesize’.

I assumed that Dune obeys the physical, chemical, and other laws of science as we know them from Earth.

My essay, and the other essays in the book, discusses the science of Dune, and I observed known terrestrial scientific laws in my attempt to explain which elements of Herbert’s Duniverse could possibly exist. Science consists of developing testable hypotheses, experimentally testing these hypotheses, and evaluating the experimental results to determine whether these support our hypothesis, or if we must reject it and generate a new hypothesis.

Since we are (so far) limited to performing experiments on Earth (and a very few in space) and have not yet visited any other planets to observe and measure conditions there, we can test hypotheses only under terrestrial conditions.

If we postulate that a planet or organism does not follow known laws, but instead follows another set of to us, unknowable and untestable laws, then we have left the realm of science and entered the realm of science fiction. Herbert, as a science fiction author, presents a planet, Dune, that violates terrestrial laws in several instances. I’ll mention which of his creations and speculations are impossible on Earth, and why.
In future posts I’ll try to address:

oxygen production, plate tectonics and volcanic activity, and sandworm biology in greater depth.

To comment, click the red number to the right of the blog’s title.
Further reading:

George Santayana, Reason in Science Volume 5 of the Life of Reason, Collier Books.

Carl Sagan, The Demon-Haunted World: Science as a Candle in the Dark, Random House, (1996).

Stephen S. Carey, A Beginner’s Guide to Scientific Method, Wadsworth Publishing; 3 edition (2003).

Robert M. Martin, Scientific Thinking, Broadview Press (1997).

Hugh G. Gauch Jr., Scientific Method in Practice, Cambridge U. Press (2002).

Barry Gower, Scientific Method: A Historical and Philosophical Introduction, Routledge (1996).

Peter Achinstein, Science Rules: A Historical Introduction to Scientific Methods, Johns Hopkins U. Press (2004).

M. Taper, S. Lele (Eds.), The Nature of Scientific Evidence: Statistical, Philosophical, and Empirical Considerations, U. Of Chicago Press (2004).

H. Bauer, Scientific Literacy and the Myth of the Scientific Method, University of Illinois Press (1994).

W. I. Beveridge, The Art of Scientific Investigation, Blackburn Press (2004).

M. Cohen, An Introduction To Logic And Scientific Method, Hughes Press (2007).

Dune: Biology of the Sandworm
Posted by sibylle in books, films, photography, Science of Dune (Wednesday January 9, 2008 at 8:40 pm)

Dune.jpg

This month, BenBella Books published The Science of Dune: An Unauthorized Exploration into the Real Science Behind Frank Herbert’s Fictional Universe, which contains my essay, “The Biology of the Sandworm”. In the essay, I speculate about what would be the characteristics of a 200-meter long sandworm living on a dry, desert planet like Frank Herbert’s Dune. How large can an animal get? And what would the sandworm eat on Dune? How does an animal that large move? And what’s its lifecycle? Where does the oxygen come from, since few to no photosynthetic plants grow on Dune’s surface?

I can hardly claim to answer all, or even most of these questions, but I do postulate several possibilities never envisioned by Herbert (after all, this book is unauthorized). Also, biology has advanced considerably since Herbert first created Dune in 1965, and I rely on new scientific findings to explain how the sandworm could possibly survive and flourish on Dune.

While I’ve been writing about science for years, I generally write about scientific meetings and interview speakers about their latest research. Such work appeared in New Scientist, Red Herring, HMS Beagle, Reuters Health, and other magazines and websites. This, my first foray into the science of fictional creatures on imaginary planets, has proven to be surprisingly controversial. I hope to respond to some of the questions posed in the coming weeks, once I either start another blog to deal with science writing, or metamorphose this one into a biology blog for a time.

Please leave your comments as to whether you’d like to hear about sandworm biology on this blog. To comment, click the red number to the right of the blog’s title.

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