Tag Archives: Carbon-based Life

Harvard astrophysicist backs the Rare Earth hypothesis

What is the Rare Earth hypothesis?

It’s the thesis of a recent book written by two scientists at the University of Washington.

Here’s the blurb:

What determines whether complex life will arise on a planet? How frequent is life in the Universe?

In this exciting new book, distinguished paleontologist Peter D. Ward and noted astronomer Donald Brownlee team up to give us a fascinating synthesis of what’s now known about the rise of life on Earth and how it sheds light on possibilities for organic life forms elsewhere in the Universe.

Life, Ward and Brownlee assert, is paradoxically both very common and almost nowhere. The conditions that foster the beginnings of life in our galaxy are plentiful. But contrary to the usual assumption that if alien life exists, it’s bound to be intelligent, the authors contend that the kind of complex life we find on Earth is unlikely to exist anywhere else; indeed it is probably unique to our planet.

With broad expertise and wonderful descriptive imagery, the authors give us a compelling argument, a splendid introduction to the emerging field of astrobiology, and a lively discussion of the remarkable findings that are being generated by new research. We learn not only about the extraordinary creatures living in conditions once though inimical to life and the latest evidence of early life on Earth, but also about the discoveries of extrasolar planets, the parts Jupiter and the Moon have played in our survival, and even the crucial role of continental drift in our existence.

Insightful, well-written, and at the cutting edge of modern scientific investigation, Rare Earth should interest anyone who wants to know about life elsewhere and gain a fresh perspective on life at home which, if the authors are right, is even more precious than we may ever have imagined.

And here’s a review by Library Journal:

“Renowned paleontologist Ward (Univ. of Washington), who has authored numerous books and articles, and Brownlee, a noted astronomer who has also researched extraterrestrial materials, combine their interests, research, and collaborative thoughts to present a startling new hypothesis: bacterial life forms may be in many galaxies, but complex life forms, like those that have evolved on Earth, are rare in the universe. Ward and Brownlee attribute Earth’s evolutionary achievements to the following critical factors: our optimal distance from the sun, the positive effects of the moon’s gravity on our climate, plate tectonics and continental drift, the right types of metals and elements, ample liquid water, maintainance of the correct amount of internal heat to keep surface temperatures within a habitable range, and a gaseous planet the size of Jupiter to shield Earth from catastrophic meteoric bombardment. Arguing that complex life is a rare event in the universe, this compelling book magnifies the significance — and tragedy — of species extinction. Highly recommended for all public and academic libraries.”

Note that Peter Ward is a militant atheist (he has debated against Stephen C. Meyer), and Donald Brownlee is an agnostic. These are not Christians, nor are they even theists. However, I have the book, I have read the book, and I recommend the book. I usually have this book on my shelf at work for show-and-tell.

Now for the latest news about the hypothesis of the book. (H/T Brian Auten of Apologetics 315)

There are always going to be optimistic predictions by scientists who need to attract research funding, but those are hopes and speculations. The data we have today says Earth is rare. The number of conditions required for complex life of any kind is too high for us to be optimistic about alien life in this galaxy, at least. And as the number of requirements for life roll in, the odds of finding alien life that can contact us get slimmer and slimmer.

From the UK Daily Mail. (H/T Peter S. Williams)


Dr Howard Smith, a senior astrophysicist at Harvard University, believes there is very little hope of discovering aliens and, even if we did, it would be almost impossible to make contact.

So far astronomers have discovered a total of 500 planets in distant solar systems – known as extrasolar systems – although they believe billions of others exist.

But Dr Smith points out that many of these planets are either too close to their sun or too far away, meaning their surface temperatures are so extreme they could not support life.

Others have unusual orbits which cause vast temperature variations making it impossible for water to exist as a liquid – an essential element for life.

Dr Smith said: ‘We have found that most other planets and solar systems are wildly different from our own.

‘They are very hostile to life as we know it.’

‘The new information we are getting suggests we could effectively be alone in the universe.

‘There are very few solar systems or planets like ours. It means it is highly unlikely there are any planets with intelligent life close enough for us to make contact.’ But his controversial suggestions contradict other leading scientists – who have claimed aliens almost certainly exist.

These arguments are actually quite useful, and I include them in my standard list of scientific arguments for theism. (See below) You have to know this stuff cold. Most people believe in aliens because they watched movies made by artists. As a result, they think that humans are nothing special and that God is not interested in us in particular. Which is very convenient for them, because it means they can do whatever they want and not care what God thinks about what they are doing. If you want to defend against the idea that humans are nothing special, and that we were not placed here for a purpose, and that we are not accountable and obligated to seek and know the Creator/Designer, then you’ll need more than feelings. You’ll need science. You’ll need the best science available.

Related posts

What are galactic habitable zones and circumstellar habitable zones?

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.

Is carbon required for complex life? Is the production of carbon fine-tuned?

Here’s an article by Fuz Rana at Reasons to Believe, talking about alternatives to carbon-based life. (H/T Tough Questions Answered)


Life as we know it on Earth consists of carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur (CHONPS). But could other elements constitute life as we don’t know it?

Not merely a discussion topic for science-fiction buffs, this question bears on origin-of-life discussions and on the search for extraterrestrial life. Carbon-based life requires a strict set of conditions. But perhaps life based on an element like silicon can exist under more extreme conditions. Few places in our solar system, and presumably beyond, can conceivably support carbon-based life. But for life built upon silicon, habitable sites may well abound throughout the universe.

However, of the 112 known chemical elements, only carbon possesses sufficiently complex chemical behavior to sustain living systems.  Carbon readily assembles into stable molecules comprised of individual and fused rings and linear and branched chains. It forms single, double, and triple bonds. Carbon also strongly bonds with itself as well as with oxygen, nitrogen, sulfur, and hydrogen.

Carbon serves as the hub of complex molecules. You can join lots of different things to it so that they stay put. But the bonds are not so strong that you can’t break things apart if you really want to. That’s what makes it suitable for making complex life, and why people talk about “carbon-based life”.

The rest of the article explains why other kinds of elements like silicon and phosphorus are not suitable for creating life.

Is carbon synthesis fine-tuned?

Here’s an article by agnostic physicist Paul Davies explaining why people think that the production of carbon in the universe is an example of fine-tuning.


One of the best-known examples of this life-friendly ‘fine-tuning’ of the laws of physics concerns carbon, the element on which all known life is based. The Big Bang that kicked off the universe coughed out plenty of hydrogen and helium, but no carbon. So where did the carbon in our bodies come from? The answer was worked out in the 1950s: most of the chemical elements heavier than helium were manufactured in the cores of stars, as the product of nuclear fusion reactions. It is the energy released by these reactions that makes the Sun and stars shine.

However, while the details of stellar nuclear reactions are fairly straightforward, there is a notable exception: carbon. Most nuclear reactions in stars occur when two atomic nuclei, rushing around at tremendous speed care of the searing temperatures, collide and fuse, forming a heavier element. But carbon cannot be made this way because all the intermediate steps from helium to carbon involve highly unstable nuclei. The solution, spotted by University of Cambridge astronomer Fred Hoyle, is for carbon to form from the simultaneous collision of three helium nuclei.

THERE IS, HOWEVER, a snag. The chances that three helium nuclei will come together at the same moment are tiny. So Hoyle reasoned that a special factor must be at work to boost the rare reaction and lead to our abundance of carbon. If not, then life in general, and Fred Hoyle in particular, would not exist!

Hoyle knew that nuclear reactions can sometimes be greatly amplified by the phenomenon of resonance, similar to the way that an opera singer can shatter a glass by hitting a certain pitch. Carbon nuclei can resonate too, if the masses and energies of the colliding particles that go to form it are just right. Hoyle worked backwards — he knew the particle masses and energies, and he used them to predict the existence of a carbon resonance.

He then pestered Willy Fowler, a nuclear physicist at the California Institute of Technology, to do an experiment to test the prediction. And sure enough, Hoyle was right. Carbon has a resonant state at exactly the right energy to enable stars to manufacture abundant carbon, and thereby seed the universe with this life-encouraging substance.

Hoyle immediately realised just what a close-run thing this mechanism is. Like Baby Bear’s porridge in the story of Goldilocks, the energy of the carbon resonance has to be “just right”. Too high or too low, and the consequences for life would be catastrophic.

So what determines the carbon resonance? Ultimately it depends on the strength of the force that binds protons and neutrons together in the nucleus. That force is one of the unexplained parameters of basic physics — one of the knobs on the Designer Machine if you like. If the strength of the force that determined the carbon resonance was only a fraction stronger or weaker, it is doubtful there would be observers in the universe to worry about the distinct absence of carbon.

Hoyle himself was deeply impressed by this discovery. “It looks like a put-up job,” he quipped. “A commonsense interpretation of the facts suggests that a superintellect has monkeyed with physics,” he later wrote. A similar conclusion was reached by the Princeton physicist Freeman Dyson: “In some sense, the universe knew we were coming.”

He doesn’t accept that God is the fine-tuner though, so the article just concludes with “it could be” speculations, which is all that naturalists can offer against the standard theistic arguments. Still, what he said about the finely-tuned synthesis of carbon is accurate.

Does God exist? Is there any scientific evidence to prove that God exists?

Since I haven’t talked about science in a while, I thought that now would be a good time to list some of the more common arguments for a Creator and Designer of the universe and/or intelligent life. I like to use arguments drawn from mainstream science that do not assume the Bible or inerrancy or anything specifically religious. The arguments below all show that the reality we live in exhibits effects in nature that are not explained by particles in motion, chance and the operation of natural laws.

First, here’s the list of a few of the better-known arguments:

The average knuckle-dragging atheist will not be familiar with any of these arguments, will have never seen them used in academic debates, and will not even click through to read about them. That’s atheism these days – it’s non-cognitive. Atheism is all about escaping from moral values and moral obligations, which are not even rationally grounded by atheism.

The point of being familiar with these arguments is to show that religion and science are virtually identical. Both are trying to explain the external world. Both are bound by the laws of logic. Both use evidence to verify and falsify claims. For example, the discovery of the origin of the universe falsifies Hinduism, Buddhism and Mormonism, but it leaves Christianity, Islam and Judaism unscathed. All religions make truth claims and those claims can be tested against what science tells us about the world.

What is the significance of scientific progress for Christians?

Some general points to know when presenting these arguments.

1. You need to emphasize that atheism is in full flight away from the progress of science. Each of these arguments has gotten stronger as the evidence grew and grew. For example, scientists had to be forced to turn away from the eternal universe as new discoveries arrived, such as the cosmic microwave background radiation measurements. Scientists had to turn away from the view that the cosmological constants are nothing special, as more and more fine-tuned quantities were discovered.

2. Christians need to pay attention in school and score top grades in mathematics and experimental sciences. Science is God-friendly, and we need to have Christians doing cutting edge research in the best labs at the universities. Think of the work done by Doug Axe at Cambridge University in which he was able to publish research showing that very few sequences of amino acids have biological function, so getting functional sequences at random is virtually impossible. One of Doug’s papers is here. We need more people like him.

3. Each of these arguments needs to be studied in the context of polemics and debates. The best way to present each of these arguments is by presenting them as a struggle against opposing forces. For example, when talking about the big bang, emphasize how atheists kept trying to come up with eternal universe speculations. When talking about the fine-tuning, talk about the unobservable multiverse. When talking about irreducible complexity, talk about the co-option fallacy. Don’t preach – teach the controversy.

4. Don’t make lazy excuses about how scientific evidence doesn’t persuade non-Christians. Science is absolutely the core of any argument for Christianity, along with the case for the resurrection of Jesus. Christianity is about knowledge. Christians who refuse to subject their faith to science are probably just trying to make sure that Christianity isn’t so true that it dictates how they should live. They like the uncertainty of blind faith, because it preserves their autonomy to disregard Christian moral teachings when it suits them.

5. The purpose of linking your Christian faith to scientific arguments is to demonstrate to non-Christians that Christianity is real. It is not a personal preference. It is not something you grew up with. It is not something you inherited from your parents. When you link your Christian faith with scientific facts in the external world, you are declaring to non-Christians that Christianity is testable and binding on everyone who shares the objective reality we live in. You can’t expect people to act Christianly without showing that Christianity is objectively true.

6. Scientific arguments are tremendously useful even for believing Christians, because sometimes it is difficult to act in a Christian way when your emotions are telling you not to. When your feelings make it hard for you to behave Christianly, that is when scientific evidence can come into play in order to rationally justify acts of self-denial and self-sacrifice. For example, scientific evidence for the existence of God is a helpful counterbalance to the problem of apparently gratuitous evil, which often discourages Christians.

My complete index of arguments for and against Christian theism is here.

UPDATE: I notice that in the popular culture, people are not really aware of these arguments, and are still arguing for religious faith based on pragmatism and personal experience, not on evidence. Using reason and evidence is much better, and it’s what the Bible teaches, too.

What conditions are needed to create a habitable planet?

UPDATE: Welcome, visitors from Post-Darwinist! Thanks for the link Denyse! New visitors may be interested in this post, which is a jumping off point for all of posts on science and faith issues.

Everyone who isn’t Christopher Hitchens or Richard Dawkins already knows about the standard fine-tuning argument. But have you ever considered what it takes to make a planet that is capable of supporting the minimal requirements of living systems? The area of science that specializes in answering this question is called astrobiology. Let’s take a look!

I will be working from a lecture (with Q&A) delivered in October 2007 at California State University – Fresno, by two of my favorite scholars, Jay Wesley Richards and Guillermo Gonzalez.

The Copernican Principle

Richards introduces the idea of the Copernican Principle. This principle states that the progress of science will show that there is nothing special (designed) about man’s place in the universe.

The minimal requirements for life

I’ve written about this before here, but basically life requires a minimum amount of encoded biological information to allow it to replicate itself. The only element in the periodic table that allows you to encode information is carbon. Carbon is the hub of large molecules which form the paper and text of biological information. No carbon = no life.

Secondly, you need some environment in which to form molecules around the carbon, such as amino acids and proteins. That environment is liquid water. And you need the liquid water to be at the surface the planet where you want life to exist.

The requirements of a habitable planet

Here are just a few of the requirements mentioned in the lecture.

  • 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

Note that these requirements are connected. If you mess with one, some of the others will be thrown out of tune. For more habitability requirements, see this article by Gonzalez and Richards.

What are the probabilities that we will get these conditions?

Richards explains that the question of whether this is designed is like winning the lottery. Your chance of winning depends on two things:

  1. the odds of getting all the conditions correct
  2. the number of tries that you get

If the odds of winning are 1 in a million, you could still win by buying a million tickets with all the different numbers. In the universe, there are only about 10^22 possible solar systems. So if the odds of getting a habitable planet are 1 in 10^9, you’ll get tons of life. But what if the odds are 1 in 10^40? Then you’re not likely to win.

But this is not the argument that these two are making, because even though there are a lot of factors needed for a habitable planet, we still can’t say for certain how likely it is that each of these conditions will obtain. Therefore, we can’t make the argument except by estimating the odds of getting each condition.

Although you could use very generous estimates, it would still be guessing, and you can win a debate by guessing. So are we stuck?

How to make a design argument using habitability

Gonzalez explains why you can still make an argument for design by arguing that the coorelation between habitability and measurabiliy is intentional. (By measurability, he really means the ease of making scientific discoveries). And you do this by correlating the conditions for sustaining life with the conditions for allowing scientific discoveries.

Gonzalez gives two examples:

  1. Solar eclipses require that the sun and moon have certain sizes and certain distances from the sun. The surface of the Earth is the optimal location in our solar system for observing solar eclipses. We were able to make many valuable discoveries due to this fine-tuning, not the least of which was confirming the theory of general relativity, which was cruicial to the science of cosmology.
  2. The location of our solar system is fine-tuned within two spiral arms of a spiral galaxy. We escape from radiation and other dangers, but to also allow use to capture heavy elements that are needed to make a suitable Sun and humans bodies, too. But the same conditions that allow life also allow us to make scientific discoveries, such as star formation theory and cosmic microwave background radiation measurements, which was needed in order to confirm the creation of the universe out of nothing (the big bang).

Spooky. And what until they list off a half-dozen more examples in their book “The Privileged Planet”. It’s downright terrifying!


Richards sums up the argument with an illustration. He asks why scientists construct observatories high up on mountains. The answer is in order to avoid “light pollution” from nearby cities, which ruin the ability of scientists to observe the stars and make discoveries. And this is what we see with our planet and solar system. No one builds a planet that can be used to make scientific discoveries in a place that doesn’t support life. It turns out that the very places in the universe that are good for making observations are also the best places for supporting life.

Further study

I would recommend checking out the documentary DVD, if you find the book too scary. There is also a university lecture DVD with both authors, filmed at Biola University. If you want to see the DVD online for FREE, then click here (narrated by John-Rhys Davies). Awesome! Go science!