Hold on tight, we’re in for a bumpy ride.
At some point soon, Earth's magnetic poles will flip, and compasses will point south instead of north.
Over the last 20 million years, Earth's magnetic field has flipped its polarity about once every 200,000 to 300,000 years. For the last 780,000 years, we've been stuck in our current magnetic configuration, although there are signs that right now something is afoot. Earth's magnetic field appears to have been weakening at a rate faster than you'd get with normal variations. And there's a patch inside the Earth underneath southern Africa that appears to have reverse polarity – if you could use a compass down there, the arrow would point south. This is the sort of behaviour we might expect if a pole reversal was on its way.
ESA / ATG Medialab / Via esa.int
So whether it's happening now, or will happen in a few hundred years or more, scientists are pretty sure that a pole reversal is on its way eventually.
Exactly how magnetic field reversals start is not fully understood, but we do know that Earth's magnetic field has flipped hundreds of times over the last 3 billion years, and there appears to have been no huge detrimental effects. If the field weakened a lot or disappeared entirely, our power and communications systems might be in trouble – but there's no evidence a total disappearance has ever happened in the past.
OK, so, to be clear, this one mostly sounds terrifying but will probably be fine in the grand scheme of things.
NASA/Gary Glazmaier
In a billion years, Earth will get so hot the oceans will evaporate.
Since the sun formed, 4.5 billion years ago, it's become about 30% brighter than it was in the beginning. In the next billion years, it's due to get 10% brighter again. Which is sad for us, because it means the oceans are going to start evaporating.
The habitable zone around a star is where liquid water can exist. Estimates of the habitable zone around the sun vary but conservative ones put Earth just inside the zone. The state of the planet or body plays a part, too, though. For example, Mars is generally considered to fall inside the habitable zone around our sun but less than a third of the planet has the right atmospheric pressure and temperature for liquid water (if there was any water on Mars in the first place).
In about a billion years, the habitable zone around the sun will move further away and Earth won't be in it any more.
There's some debate over how quickly this process will happen, but once Earth gets hot enough for the oceans to start evaporating, it's likely to create a feedback loop. Water vapour is a greenhouse gas, so as it evaporates into the atmosphere the planet will heat up more, and more water will evaporate, until, eventually, the ground is dry and the atmosphere is saturated. From there, water will escape into space.
Evgeniysmolskiy / Getty Images
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