If The Earth Were A Person How Old Would It Be?


Whenever I’m feeling worn down by the nitty-gritty minutiae of modern life, I console myself with one little fact. A fact that is remarkably powerful when it comes to clearing my head and giving me the fresh perspective I need to grind through another day of being importuned by ignorance, injustice and inanity.

“Who gives a crap?” I ask myself. “One day the sun will blow up and destroy the planet anyway.”

Yes, it’s true. In about 5 billion years, our happy little sun is going to hulk up and erase Gaia from existence. When I found that out as a child I felt very sad. The illusion of an eternity underpinning everything was gone. I knew that it wouldn’t affect me personally, or anyone I would ever know, but I felt sorry for those future humans slowly getting roasted by the engorged sun.

Okay, so the sun won’t ‘explode’ in a supernova. Our yellow dwarf will in about 5 billion years use up all of its hydrogen and become a red giant. The circumference of the sun will expand two-hundredfold. Which means that Mercury and Venus will be engulfed. The sun will continue to swell, and it will be touch and go as to whether the Earth will be swallowed. Aiding our planet is the fact that as it expands, the sun will eject mass in the form of solar winds. As the sun loses mass, its gravitational pull on the Earth will lessen, and Earth’s orbit will expand.

Not quite enough, though. Eventually, like Bhodi at the end of Point Break, the Earth has gotta go down.

Two astronomers, K.P. Schröder and R.C. Smith, crunched the numbers in 2008 in their paper “Distant future of the Sun and Earth revisited”. Which sounds more like a prog rock concept album from the seventies than an academic paper. In the paper they confirm that, yes, the planet will die. It amazes me that humans can know this. That we are able to work out how suns evolve, how old the Earth is, how and when the Earth will return to stardust. Adds to the poignancy of it all, really. Cue Joni Mitchell.

Now that those prophets of doom have given us a death-date for the Earth, we can consider the life span of the Earth. To give us a handle on this vast length of time, let’s try our hands at some anthropomorphism. How old would the Earth be if it were human? Assume for the sake of this exercise that a human life is your biblical three score years and ten, and whack another ten on for advances in medical science. Eighty years.

The Earth is about 4.5 billion years into a 9.5 billion year life-span. On a human life-span scale, the Earth would be… (carry the one…) 37.9 years old.

Still in its prime, but with a bit of a middle age spread starting to show. Career beginning to peak, but wondering if it’s really found its passion. Starting to enjoy spending nights at home with a bottle of wine and some streaming seasons of a well-scripted docu-drama instead of ingesting synthetic drugs and dancing to appalling techno music until dawn. Developing an interest in interior decorating. Realising that although life isn’t over yet, many of the dreams it had on its ‘bucket list’ are probably fading in likelihood. Looking back on its crazy ‘dinosaur phase’ fondly, but not really up for that kind of excitement anymore.

You get the gist of what I’m going for, here.

One thing jumps out at you when reading Schröder and Smith’s paper, as you skim past the many equations and try to find the bits written in English. Prior to the sun promoting itself to red giant status, it will increase in luminosity by 10% every 100 million years or so. To wit, it will get hotter. In fact, in about a billion years the sun will be so hot that the oceans of Earth will have boiled away. Meaning life as we know it will be long gone by the time the sun goes ker-flooey.

So, to revise my earlier statement in order to make it more scientifically accurate:

“Who gives a crap? In approximately a billion years, the gradual increase in luminosity of the sun will make life on Earth untenable anyway.”

Hmm. Maybe not quite as catchy.

While we’re thinking of the lifespan of the Earth in human terms, I wonder how long will our home spend in its ‘human phase’? We evolved about 200,000 years ago. Let’s be generous and give ourselves another mil to either develop into something else, or wipe ourselves out with a nanotech disaster of some kind. So, of the 9.5 billion years of the Earth’s lifespan, we occupy 1.2 million years. Carry the one again…

About 4.2 days out of eighty years.

A long weekend. That’s all we are to the Earth. A brief relationship, a holiday fling forgotten faster than it will take for the corn rows to come out and the tan to wear off.