Once there was a world not so very different from our own.
There were occasional natural catastrophes, massive volcanic eruptions and, every once in a while, an asteroid would come barrelling out of the blue to do some damage.
But for the first billion years or so, it would’ve seemed like a paradise, the very personification of its name: The Goddess of Beauty.
Then things started to go horribly wrong.
The planet Venus, which once may have seemed like a heaven, turned into a kind of hell. The difference between the two can be a delicate balance, far more delicate than you might imagine.
Once things began to unravel, there was no way back.
Venus’s oceans are long gone. The surface is hotter than a broiling oven, hot enough to melt lead. Why? You might think it’s because Venus is 30% closer to the Sun than the Earth is, but that’s not the reason. Venus is completely covered by clouds of carbon dioxide and sulphuric acid; the latter keeps almost all the sunlight from reaching the surface. That ought to make Venus much colder than the Earth.
So why is Venus scorching hot? It’s because the small amount of sunlight that trickles in through the clouds to reach the surface can’t get back out again. The flow of energy is blocked by the dense atmosphere of carbon dioxide. That carbon dioxide gas – or CO2 for short – acts like a smothering blanket to keep the heat in.
No one is burning coal or driving big petroleum-guzzlers on Venus. Nature can destroy an environment without any help from intelligent life.
Venus is in the grip of a runaway greenhouse effect.
In 1982, the scientists and engineers of what was then the Soviet Union successfully landed Venera 13 on Venus. They managed to keep it refrigerated for over two hours, so it could photograph its surroundings and transmit the images back to Earth before the onboard electronics were fried.
Venus and Earth started out with about the same amount of carbon, but the two worlds were propelled along radically different paths, and carbon was the decisive element in both stories. On Venus, it’s almost all in the form of gas – carbon dioxide – in the atmosphere.
Most of the carbon on Earth has been stored for aeons in solid vaults of carbonate rock, like limestone and chalk. How? Volcanoes supply carbon dioxide to the atmosphere, and the oceans slowly absorb it. Working over the course of millions of years, microscopic algae harvest the carbon dioxide and turn it into tiny shells. They accumulate in thick deposits of chalk, or limestone. Other marine creatures take in carbon dioxide to build enormous coral reefs. And the oceans convert dissolved CO2 into limestone even without any help from life. As a result, only a trace amount is left as a gas in Earth’s atmosphere. Not even three-hundredths of one per cent.
Think of it – about four molecules out of every ten thousand. And yet, it makes the critical difference between a barren wasteland and a garden of life on Earth. With no CO2 at all, the Earth would be frozen. And with about twice as many, we’re still talking about only six molecules out of ten thousand, things would get uncomfortably hot and cause us some serious problems.
But never as hot as Venus; not even close. That planet lost its ocean to space billions of years ago. Without an ocean, it had no way to capture CO2 from the atmosphere and store it as a mineral. The CO2 from erupting volcanoes just continued to build up.
Today, that atmosphere is 90 times heavier than ours. Almost all of it is heat-trapping carbon dioxide. That’s why Venus is such a ferocious inferno – so hostile to life.