Why I am a Christian (3)

The Dimensions, Properties, Proportions and Situation of the Earth Appear Wisely Chosen

In 2012, I jotted down all the reasons I could think of why I am a Christian. I came up with 26. I then placed them under the categories of cosmological/astrobiological, existential/philosophical, theological, Christological, scriptural and personal/experiential.

The first four reasons (to do with the origins of the universe, the fine tuning of the universe, the life-favouring properties of the Earth and the improbable appearance of organic matter on Earth) are cosmological or astrobiological in nature and they contribute to my understanding as to why I think that my belief in a creator is credible and not unreasonable. 

So this is the third of 26 reasons I am a Christian; the dimensions, properties, proportions and situation of the Earth appear to have been wisely chosen. If there was even a little variation to what we have on Earth, intelligent life as we know it would not be possible at all.

Ever since human beings have realised they live on a spinning planet and looked up to the heavens at other moving spheres they have wondered if we are alone in the universe. Could intelligent life or even microscopic, unicellular life have appeared anywhere else?

Relatively recently, the Kepler telescope has discovered planets in other solar systems and has been able to work out if, due to their size, their distance from their star and their probable elemental constitution, they are the type of planets that might be able to support life. At the 221st meeting of the American Astronomical Society in California earlier this month astronomers speculated that perhaps one in six stars hosts an Earth-sized planet in close orbit. 

I have no more idea whether extraterrestrial life exists than anyone else. But the conditions necessary for complex life forms like human beings appear to be many and varied. Our Earth seems uncannily well suited to provide for us a good home. 

Seven different factors, each very precisely just right, favour the emergence and sustenance of life on Earth. (Bill Bryson, in his excellent book A Short History of Nearly Everything says there are in fact 40 factors but I’m sticking at 7!)

Firstly, our distance from the Sun (about 150 million kilometres or 8 light-minutes away) happens to be just right. Our nearest neighbour towards the sun, Venus, (about 41 million kilometres closer) has a surface temperature of about 450 degrees C. Our nearest neighbour away from the sun, Mars, plunges to -140 degrees C at its coldest. Bill Bryson comments that if the Earth were just 5% nearer the Sun or 15% further away from it, we would no longer be situated in a habitable zone. These are very small distances astronomically speaking. A shade closer to our star (in cosmological terms) and the oceans would boil. A little further away and our good Earth would be an inhospitable ball of rock and ice.

As Goldilocks noted, one bowl of porridge was too hot, one was too cold but one was just right. The Earth’s properties being just right for life, (and not just in the area of surface temperature) it has what some have called the Goldilocks effect.

Secondly, the Earth happens to spin round just the right sort of star. Smaller stars do not have the strength necessary to power life on a planet like Earth. And, though it may seem odd, bigger stars burn their fuel much more quickly. But stars like the Sun have enough hydrogen and helium to last about ten billion years so we’re not even half way through yet. Astronomer Dr. Guillermo Gonzalez and Philosopher of Science Dr. Jay Richards have said it would take a star with the highly unusual properties of our Sun; the right mass, the right light, the right age, the right distance, the right orbit, the right galaxy, the right location in the galaxy - to nurture living organisms on a circling planet. 

Thirdly, the size of the Earth is just right to support a life-sustaining atmosphere. By contrast, the Moon, for example, is too small a sphere so its weaker gravitational attraction fails to hold any gases to its surface. Having an atmosphere is absolutely vital to us, way beyond supplying us with breathable air. It evens out temperature scales between night and day (one reason why the scale is so wide-ranging on Mars is that its atmosphere is much thinner), it warms the surface of the planet through the greenhouse effect, it filters out harmful solar radiation and it burns up all but the largest (and rarest) asteroids heading our way.

Fourthly, our Earth has just the right mix of key elements in just the right quantities, especially an abundance of liquid water at the surface. By contrast Venus, for example, is largely sulphurous at the surface and with a dense atmosphere of carbon dioxide and clouds of sulphuric acid. Only 0.05% of the earth’s crust is carbon but that’s enough – in fact, just enough. Life is not possible without carbon but even slightly too much of it is a very bad thing – that’s why Venus has a runaway greenhouse effect and an atmosphere hot enough to melt lead.

Fifthly, our Earth has just the right foundation at its core; a vast iron centre. The ferric interior of our planet gives the Earth a magnetic field arising from convection currents in the liquid outer core. Without our magnetic field, our atmosphere would slowly erode altogether through solar wind (sudden and massive bursts of energy from the Sun’s atmosphere). As Chris Wickham writes: “The only thing stopping Earth having a lifeless environment like Mars is the magnetic field that shields us from deadly solar radiation."

Those pretty Northern Lights we admire in the Arctic Circle are in fact a massive solar radiation attack in which our magnetic shield is saving us from being fried alive in our beds.

Sixthly, our Earth has just the right conditions on its crust; plate tectonics. Our planet’s surface is constantly shifting. The outer crust is made up of vast slabs of land that move towards and away from each other. There is a growing conviction among planetary scientists that plate tectonics are necessary for life because they replenish the nutrition that primitive life depends on and recycle carbon around the planet. Not only that, but plate tectonics, over many, many years, elevate landmasses and produce mountainous regions. This is vital to us because if the land on our planet were uniformly flat, it would all be submerged under about 4 kilometers of sea.

Seventhly, our Earth has a Moon; the largest in the solar system in relation to its host planet. The Moon is just right in terms of size and distance from Earth to stabilize our planet’s axial tilt so avoiding significant, rapid and life-threatening climate changes. The absence of a moon for Mars has been the other main cause of fluctuations in temperature spanning 180 degrees C.  Our Moon is big enough and close enough to command tidal flows around our coasts but not so big or so near that it completely engulfs our landmasses with tsunami-like tides every time it passes above us.

Of course, some argue that this view is the wrong way round and that life has simply adapted and tuned itself to the conditions available on earth. But if that were true wouldn't we have discovered abundant life elsewhere in space?

In short, I marvel that our planet pulsates with life because it is, in every way, just right for life to thrive. We take for granted how well life flourishes on Earth. But if any of the features listed above were a fraction different from the way they are, life as we know it would not be possible here. Like the instantaneous creation of everything from nothing (Reason 1) and the incredibly precise physics necessary for it all to happen (Reason 2) it all appears to have been carefully arranged.

For this is what the Lord says—
he who created the heavens, he is God;
he who fashioned and made the earth,
he founded it; he did not create it to be empty,
but formed it to be inhabited—
he says: “I am the Lord, and there is no other."

(Isaiah 45.18)

On its own, Reason 3 would certainly never be anywhere near enough to convince me that God exists, let alone that Christianity is true.

As former Professor of Mathematical Physics at the University of Cambridge (and Anglican clergyman) John Polkinghorne put it: “A big, fundamental question, like belief in God (or disbelief), is not settled by a single argument. It’s too complicated for that. What one has to do is to consider lots of different issues and see whether or not the answers one gets add up to a total picture that makes sense.”

I agree. I have 26 reasons that incline me to believe that it is true and that he does exist. This is only number 3.

But, though it is an improbable marvel that any planet with exactly the right conditions for flourishing life exists at all, the greater wonder by far is how even the very simplest life forms could just create themselves from nonliving components. We're back to probabilities in numbers with lots and lots and lots of zeroes. That’s what I’ll muse about in two weeks’ time.