Life on Earth: Is our planet special?
Far from being unique, many now regard Earth as an ordinary lump of space rock and believe that life “out there” is almost inevitable. But could the truth be somewhat more complex?
On Friday, top scientists are meeting at the Geological Society in London to debate this very issue, posing the question: “Is the Earth special?”. What emerges is that aspects of our planet and its evolution are remarkably strange.
“Well, there are several unusual aspects of our planet,” she said. “First is our strong magnetic field. No one is exactly sure how it works, but it’s something to do with the turbulent motion that occurs in the Earth’s liquid outer core. Without it, we would be bombarded by harmful radiation from the Sun.”
“The next thing is our big Moon,” continued Prof Grady. “As the Earth rotates, it wobbles on its axis like a child’s spinning top. What the Moon does is dampen down that wobble… and that helps to prevent extreme climate fluctuations” - which would be detrimental to life.
“Finally, there’s plate tectonics,” she added. “We live on a planet that is constantly recycling its crust. That’s another way that the Earth stabilises its climate.” This works because plate tectonics limits the amount of carbon dioxide escaping into the atmosphere - a natural way of controlling the greenhouse effect.
Too bad humans in power are currently doing everything they can to mess that up :( The more you learn about the wondrous natural coincidences that led to life on Earth, the more maddening the human race’s reckless disregard for this gift becomes. Just compare it with the alternatives:
Dr Richard Ghail, an expert on Venus at Imperial College London, is highly sceptical of this Goldilocks theory, however.
“For me, the key thing is that Venus has a lower density than the Earth,” he told the BBC. “That difference was fixed early on in the formation of the Solar System when there were lots of planetary collisions.” In the case of Venus, collisions led to accretion into a single planet, but with Earth, the lighter material was flung off to form the Moon.
One effect of Venus’s lower density is that its interior melts more easily. So, whereas the Earth has a swirling core that is part solid and part liquid, the core of Venus is entirely liquid - and strangely calm.
In Dr Ghail’s opinion, this has led to a spiral of doom for Venus. Without a turbulent core, no magnetic field was generated. And no magnetic field meant that Venus was mercilessly battered by solar radiation, causing it to lose all its water.
Because water is needed to “lubricate” plate tectonics, the crust stopped recycling. Consequently, carbon dioxide built up in the atmosphere and the greenhouse effect ran out of control. As a result, today, Venus is a lifeless inferno whose surface is hot enough to melt zinc.
Hopefully billionaire polluters and the politicians who love them can be stopped before they drive this planet to a similar fate. As for the original question about how “special” the Earth may be…
Given that Earth’s history was shaped by a single improbable event, one might be tempted to assume that life elsewhere must be extremely rare.
Wrong, argues Dr Nick Lane, a geneticist at University College London. He believes that the emergence of life is probable on any wet, rocky planet.
Dr Lane explained the reasons for his confidence, saying: “One of the most common minerals in the Universe is olivine; interstellar dust is full of it. When olivine and water mix on the seafloor, the reaction is exothermic.” That is, it gives off heat.
The environment produced by this reaction “provides analogues for all six essential processes of living organisms,” continued Dr Lane. But the especially important thing is that it releases “a rich source of chemical energy that is much easier for an organism to tap than, for example, the Sun’s energy”.
Thus, wherever olivine and water mix in large quantities, conditions are favourable for the emergence of life.
Consequently, life is not limited to planets that orbit a star; conceivably it could also exist on asteroids drifting through deep space. Simply put, “The Earth is not special,” concluded Dr Lane.
Others remain unconvinced:
Prof Conway Morris concluded: “One important jigsaw piece that is rarely mentioned in these discussions is Fermi’s Paradox.” This is the concept of the Great Silence; in other words, if life is common in the Universe, why have we not managed to contact it?
And that surely is the key. For in the absence of verifiable alien contact, scientific opinion will forever remain split as to whether the Universe teems with life or we are alone in the inky blackness.
I disagree with this conclusion, finding it rather simplistic, and, shall we say…homo-sapien-centric? Why don’t people have the imagination to conceive of sentient beings who may be nothing like us otherwise? An intelligent race of, say, aquatic creatures may not have the ability - or desire - to develop technology analogous to ours. And as Varek Raith so aptly put it, “space is stupidly big”. How long have we been tech-capable compared to the length of time such signals take to traverse interstellar distances?
Speaking for myself, I don’t for a moment believe we’re alone. There are even theories that life here was partially seeded by extraterrestial dust, so why not planets/asteroids somewhere else?
I do hope I can live long enough to see the discovery of alien life, even if it’s little more than lowly microbes. If nothing else, it would be a most amusing thumb in the eye of closed-minded fundamentalists ;)