Tag Archives: Carbon

Is silicon-based life a possible alternative for carbon-based life?

In a recent debate, atheist philosopher Alex Rosenberg responded to the cosmic fine-tuning argument presented by William Lane Craig by asserting that complex life could be other than it is. He specifically mentioned silicon-based life.

Let’s see what scientists think of his speculation, using this article from Scientific American.


Group IV of the Periodic Table of the Elements contains carbon (C), silicon (Si) and several heavy metals. Carbon, of course, is the building block of life as we know it. So is it possible that a planet exists in some other solar system where silicon substitutes for carbon? Several science fiction stories feature silicon-based life-forms–sentient crystals, gruesome golden grains of sand and even a creature whose spoor or scat was bricks of silica left behind. The novellas are good reading, but there are a few problems with the chemistry.

Indeed, carbon and silicon share many characteristics. Each has a so-called valence of four–meaning that individual atoms make four bonds with other elements in forming chemical compounds. Each element bonds to oxygen. Each forms long chains, called polymers, in which it alternates with oxygen. In the simplest case, carbon yields a polymer called poly-acetal, a plastic used in synthetic fibers and equipment. Silicon yields polymeric silicones, which we use to waterproof cloth or lubricate metal and plastic parts.

But when carbon oxidizes–or unites with oxygen say, during burning–it becomes the gas carbon dioxide; silicon oxidizes to the solid silicon dioxide, called silica. The fact that silicon oxidizes to a solid is one basic reason as to why it cannot support life. Silica, or sand is a solid because silicon likes oxygen all too well, and the silicon dioxide forms a lattice in which one silicon atom is surrounded by four oxygen atoms. Silicate compounds that have SiO4-4 units also exist in such minerals as feldspars, micas, zeolites or talcs. And these solid systems pose disposal problems for a living system.

So, first of all, it makes SAND. Second of all, it is so attracted to oxygen that it can’t easily join to make any other polymers that could be used in the chemistry of the minimal functions of a living system.


Also consider that a life-form needs some way to collect, store and utilize energy. The energy must come from the environment. Once absorbed or ingested, the energy must be released exactly where and when it is needed. Otherwise, all of the energy might liberate its heat at once, incinerating the life-form. In a carbon-based world, the basic storage element is a carbohydrate having the formula Cx(HOH)y. This carbohydrate oxidizes to water and carbon dioxide, which are then exchanged with the air; the carbons are connected by single bonds into a chain, a process called catenation. A carbon-based life-form “burns” this fuel in controlled steps using speed regulators called enzymes.

These large, complicated molecules do their job with great precision only because they have a property called “handedness.” When any one enzyme “mates” with compounds it is helping to react, the two molecular shapes fit together like a lock and key, or a shake of hands. In fact, many carbon-based molecules take advantage of right and left-hand forms. For instance, nature chose the same stable six-carbon carbohydrate to store energy both in our livers (in the form of the polymer called glycogen) and in trees (in the form of the polymer cellulose).

Glycogen and cellulose differ mainly in the handedness of a single carbon atom, which forms when the carbohydrate polymerizes, or forms a chain. Cellulose has the most stable form of the two possibilities; glycogen is the next most stable. Because humans don’t have enzymes to break cellulose down into its basic carbohydrate, we cannot utilize it as food. But many lower life-forms, such as bacteria, can.

In short, handedness is the characteristic that provides a variety of biomolecules with their ability to recognize and regulate sundry biological processes. And silicon doesn’t form many compounds having handedness. Thus, it would be difficult for a silicon-based life-form to achieve all of the wonderful regulating and recognition functions that carbon-based enzymes perform for us.

The troubling thing I find about atheists is that they seem to be under the impression that an alternative speculative explanation is a refutation of an argument that is based in evidence.

So it goes like this:

  • origin of the universe? I can speculate about a naturalistic alternative cosmology which is falsified by observations
  • cosmic fine-tuning? I can speculate about an untestable multiverse
  • origin of life? I can speculate about unobservable aliens who seeded the Earth with life
  • Cambrian explosion? I can speculate about intermediary fossils that have not yet been discovered
  • habitability? I can speculate that habitable planets exist just outside the boundary of the observable universe
  • resurrection of Jesus? I can speculate that Jesus had an unknown, identical twin brother who showed up when he died and took his place

I think that if we are going to make a worldview, we should ground it in the evidence we have today. We should not have faith in speculative theories that we heard about on Star Trek. Seriously.

What makes a planet suitable for supporting complex life?

The Circumstellar Habitable Zone (CHZ)

What do you need in order to have a planet that supports complex life? First, you need liquid water at the surface of the planet. But there is only a narrow range of temperatures that can support liquid water. It turns out that the size of the star that your planet orbits around has a lot to do with whether you get liquid water or not. A heavy, metal-rich star allows you to have a habitable planet far enough from the star so  the planet can support liquid water on the planet’s surface while still being able to spin on its axis. The zone where a planet can have liquid water at the surface is called the circumstellar habitable zone (CHZ). A metal-rich star like our Sun is very massive, which moves the habitable zone out further away from the star. If our star were smaller, we would have to orbit much closer to the star in order to have liquid water at the surface. Unfortunately, if you go too close to the star, then your planet becomes tidally locked, like the moon is tidally locked to Earth. Tidally locked planets are inhospitable to life.

Circumstellar Habitable Zone
Circumstellar Habitable Zone

Here, watch a clip from The Privileged Planet: (Clip 4 of 12, full playlist here)

But there’s more.

The Galactic Habitable Zone (GHZ)

So, where do you get the heavy elements you need for your heavy metal-rich star?

You have to get the heavy elements for your star from supernova explosions – explosions that occur when certain types of stars die. That’s where heavy elements come from. But you can’t be TOO CLOSE to the dying stars, because you will get hit by nasty radiation and explosions. So to get the heavy elements from the dying stars, your solar system needs to be in the galactic habitable zone (GHZ) – the zone where you can pickup the heavy elements you need but not get hit by radiation and explosions. The GHZ lies between the spiral arms of a spiral galaxy. Not only do you have to be in between the arms of the spiral galaxy, but you also cannot be too close to the center of the galaxy. The center of the galaxy is too dense and you will get hit with massive radiation that will break down your life chemistry. But you also can’t be too far from the center, because you won’t get enough heavy elements because there are fewer dying stars the further out you go. You need to be in between the spiral arms, a medium distance from the center of the galaxy.

Like this:

Galactic Habitable Zone
Galactic Habitable Zone and Solar Habitable Zone

Here, watch a clip from The Privileged Planet: (Clip 10 of 12, full playlist here)

The GHZ is based on a discovery made by astronomer Guillermo Gonzalez, which made the front cover of Scientific American in 2001. That’s right, the cover of Scientific American. I actually stole the image above of the GHZ and CHZ (aka solar habitable zone) from his Scientific American article (linked above).

These are just a few of the things you need in order to get a planet that supports life.

Here are a few of the more well-known ones:

  • a solar system with a single massive Sun than can serve as a long-lived, stable source of energy
  • a terrestrial planet (non-gaseous)
  • the planet must be the right distance from the sun in order to preserve liquid water at the surface – if it’s too close, the water is burnt off in a runaway greenhouse effect, if it’s too far, the water is permanently frozen in a runaway glaciation
  • the solar system must be placed at the right place in the galaxy – not too near dangerous radiation, but close enough to other stars to be able to absorb heavy elements after neighboring stars die
  • a moon of sufficient mass to stabilize the tilt of the planet’s rotation
  • plate tectonics
  • an oxygen-rich atmosphere
  • a sweeper planet to deflect comets, etc.
  • planetary neighbors must have non-eccentric orbits

By the way, you can watch a lecture with Guillermo Gonzalez explaining his ideas further. This lecture was delivered at UC Davis in 2007. That link has a link to the playlist of the lecture, a bio of the speaker, and a summary of all the topics he discussed in the lecture. An excellent place to learn the requirements for a suitable habitat for life.

How likely is it for blind forces to sequence a functional protein by chance?

How likely is it that you could swish together amino acids randomly and come up with a sequence that would fold up into a functional protein?

Evolution News reports on research performed by Doug Axe at Cambridge University, and published in the peer-reviewed Journal of Molecular Biology.


Doug Axe’s research likewise studies genes that it turns out show great evidence of design. Axe studied the sensitivities of protein function to mutations. In these “mutational sensitivity” tests, Dr. Axe mutated certain amino acids in various proteins, or studied the differences between similar proteins, to see how mutations or changes affected their ability to function properly.10 He found that protein function was highly sensitive to mutation, and that proteins are not very tolerant to changes in their amino acid sequences. In other words, when you mutate, tweak, or change these proteins slightly, they stopped working. In one of his papers, he thus concludes that “functional folds require highly extraordinary sequences,” and that functional protein folds “may be as low as 1 in 10^77.”11 The extreme unlikelihood of finding functional proteins has important implications for intelligent design.

Just so you know, those footnotes say this:

[10.] Douglas D. Axe, “Estimating the Prevalence of Protein Sequences Adopting Functional Enzyme Folds,” Journal of Molecular Biology, 1-21 (2004); Douglas D. Axe, “Extreme Functional Sensitivity to Conservative Amino Acid Changes on Enzyme Exteriors,” Journal of Molecular Biology, Vol. 301:585-595 (2000).

[11.] Douglas D. Axe, “Estimating the Prevalence of Protein Sequences Adopting Functional Enzyme Folds,” Journal of Molecular Biology, 1-21 (2004).

And remember, you need a lot more than just 1 protein in order to create even the simplest living system. Can you generate that many proteins in the short time between when the Earth cools and the first living cells appear? Even if we spot the naturalist a prebiotic soup as big as the universe, and try to make sequences as fast as possible, it’s unlikely to generate even one protein in the time before first life appears.

Here’s Doug Axe to explain his research:

If you are building a protein for the FIRST TIME, you have to get it right all at once – not by building up to it gradually using supposed Darwinian mechanisms. That’s because there is no replication before you have the first replicator. The first replicator cannot rely on explanations that require replication to already be in place.

Study: the early Earth’s atmosphere contained oxygen

Here’s a paper published in the prestigious peer-reviewed science journal Nature, entitled “The oxidation state of Hadean magmas and implications for early Earth’s atmosphere”. This paper is significant because it undermines naturalistic scenarios for the origin of life.

Evolution News explains what the paper is about.


A recent Nature publication reports a new technique for measuring the oxygen levels in Earth’s atmosphere some 4.4 billion years ago. The authors found that by studying cerium oxidation states in zircon, a compound formed from volcanic magma, they could ascertain the oxidation levels in the early earth. Their findings suggest that the early Earth’s oxygen levels were very close to current levels.

[…]Miller and Urey conducted experiments to show that under certain atmospheric conditions and with the right kind of electrical charge, several amino acids could form from inorganic compounds such as methane, ammonia, and water. Several experiments have been done using various inorganic starting materials, all yielding a few amino acids; however, one key aspect of all of these experiments was the lack of oxygen.

If the atmosphere has oxygen (or other oxidants) in it, then it is an oxidizing atmosphere. If the atmosphere lacks oxygen, then it is either inert or a reducing atmosphere. Think of a metal that has been left outside, maybe a piece of iron. That metal will eventually rust. Rusting is the result of the metal being oxidized. With organic reactions, such as the ones that produce amino acids, it is very important that no oxygen be present, or it will quench the reaction. Scientists, therefore, concluded that the early Earth must have been a reducing environment when life first formed (or the building blocks of life first formed) because that was the best environment for producing amino acids. The atmosphere eventually accumulated oxygen, but life did not form in an oxidative environment.

The problem with this hypothesis is that it is based on the assumption that organic life must have formed from inorganic materials. That is why the early Earth must have been a reducing atmosphere. Research has been accumulating for more than thirty years, however, suggesting that the early Earth likely did have oxygen present.

[…]Their findings not only showed that oxygen was present in the early Earth atmosphere, something that has been shown in other studies, but that oxygen was present as early as 4.4 billion years ago. This takes the window of time available for life to have begun, by an origin-of-life scenario like the RNA-first world, and reduces it to an incredibly short amount of time. Several factors need to coincide in order for nucleotides or amino acids to form from purely naturalistic circumstances (chance and chemistry). The specific conditions required already made purely naturalist origin-of-life scenarios highly unlikely. Drastically reducing the amount of time available, adding that to the other conditions needing to be fulfilled, makes the RNA world hypothesis or a Miller-Urey-like synthesis of amino acids simply impossible.

So here’s where we stand. If you are a materialist, then you need a reducing environment on the early Earth in order to get organic building blocks (amino acids) from inorganic materials. However, the production of these organic building blocks (amino acids) requires that the early Earth atmosphere be oxygen-free. And the problem with this new research, which confirms previous research, is that the early Earth contained huge amounts of oxygen – the same amount of oxygen as we have today. This is lethal to naturalistic scenarios for creating the building blocks of life on the Earth’s surface.

Other problems

If you would like to read a helpful overview of the problems with a naturalistic scenario for the origin of life, check out this article by Casey Luskin.


The “origin of life” (OOL) is best described as the chemical and physical processes that brought into existence the first self-replicating molecule. It differs from the “evolution of life” because Darwinian evolution employs mutation and natural selection to change organisms, which requires reproduction. Since there was no reproduction before the first life, no “mutation – selection” mechanism was operating to build complexity. Hence, OOL theories cannot rely upon natural selection to increase complexity and must create the first life using only the laws of chemistry and physics.

There are so many problems with purely natural explanations for the chemical origin of life on earth that many scientists have already abandoned all hopes that life had a natural origin on earth. Skeptical scientists include Francis Crick (solved the 3-dimensional structure of DNA) and Fred Hoyle (famous British cosmologist and mathematician), who, in an attempt to retain their atheistic worldviews, then propose outrageously untestable cosmological models or easily falsifiable extra-terrestrial-origin-of-life / panspermia scenarios which still do not account for the natural origin of life. So drastic is the evidence that Scientific American editor John Horgan wrote, “[i]f I were a creationist, I would cease attacking the theory of evolution … and focus instead on the origin of life. This is by far the weakest strut of the chassis of modern biology.”3

The article goes over the standard problems with naturalistic scenarios of the origin of life: wrong atmosphere, harmful UV radiation, interfering cross-reactions, oxygen levels, meteorite impacts, chirality, etc.

Most people who are talking about intelligent design at the origin of life talk about the information problem – how do you get the amino acids to form proteins and how do you get nucleotide bases to code for amino acids? But the starting point for solving the sequencing problem is the construction of the amino acids – there has to be a plausible naturalistic scenario to form them.

Scientists troubled by lack of simple explanation for our life-permitting moon

This entire article from Evolution News is a must-read. It talks about a recent paper by a naturalist named Robin Canup which appeared in Nature, the most prestigious peer-reviewed science journal.

So, there’s too much to quote here. I’ll grab a few snippets to give you the gist of it, then you click through and read the whole thing. 

The moon is important for the existence of a life permitting planet:

Canup knows our moon is important for life:

The Moon is more than just a familiar sight in our skies. It dictates conditions on Earth. The Moon is large enough to stabilize our planet’s rotation, holding Earth’s polar axis steady to within a few degrees. Without it, the current Earth’s tilt would vary chaotically by tens of degrees. Such large variationsmight not preclude life, but would lead to a vastly different climate.

The moon requires an improbable sequence of events:

Canup states that “No current impact model stands out as more compelling than the rest.” All are equally improbable, in other words. Indeed, they are:

It remains troubling that all of the current impact models invoke a process after the impact to effectively erase a primary outcome of the event — either by changing the disk’s composition through mixing for the canonical impact, or by changing Earth’s spin rate for the high-angular-momentum narratives.

Sequences of events do occur in nature, and yet we strive to avoid such complexity in our models. We seek the simplest possible solution, as a matter of scientific aesthetics and because simple solutions are often more probable. As the number of steps increases, the likelihood of a particular sequence decreases. Current impact models are more complex and seem less probable than the original giant-impact concept.

This is a good challenge to naturalism, but it lends support to one part of the habitability argument.

Previously, I blogged about a few of the minimum requirements that a planet must satisfy in order to support complex life.

Here they are:

  • a solar system with a single massive Sun than can serve as a long-lived, stable source of energy
  • a terrestrial planet (non-gaseous)
  • the planet must be the right distance from the sun in order to preserve liquid water at the surface – if it’s too close, the water is burnt off in a runaway greenhouse effect, if it’s too far, the water is permanently frozen in a runaway glaciation
  • the solar system must be placed at the right place in the galaxy – not too near dangerous radiation, but close enough to other stars to be able to absorb heavy elements after neighboring stars die
  • a moon of sufficient mass to stabilize the tilt of the planet’s rotation
  • plate tectonics
  • an oxygen-rich atmosphere
  • a sweeper planet to deflect comets, etc.
  • planetary neighbors must have non-eccentric orbits

This is a good argument, so if you want to learn more about it, get the “The Privileged Planet” DVD, or the book of the same name.