What if the Earth Stood Still?
There are a few options to the level of cataclysm that we choose to discuss here if the Earth’s rotation stopped. We could also make it ‘stand still’ completely in space, which means that we stop its orbital movement around the Sun as well, but the case here would be less interesting as the planet would be finished off pretty quickly and there wouldn’t be much left for discussion. For the sake of telling a story, let’s consider ‘standing still’ as in a cessation of the Earth’s axial rotation.
At this point, we may choose how abruptly we would like to rotation to stop. An important piece of information here is that the Earth rotates about its axis at a speed of 1670km/h at the equator. If the Earth suddenly stopped right now, everything on the surface would still keep spinning. This means that anything that is not attached to the bedrock would fly east at a speed of 408m/s at the equator. This speed decreases as you go up the latitudes – so people at the poles might just about survive, as well as people who were slightly off the ground i.e. on a plane, until they all got killed by the next few things to come. The continuation of the spin of objects on Earth includes that of the atmosphere and the ocean. As the atmosphere keeps travelling relative to the non-rotating Earth, this would entail the Earth’s crust being eroded clean by winds 4 times the speed of the fastest wind ever recorded on the planet. Waves of unprecedented heights would also be generated and wash the debris on land down with them.
This all would leave the surface of the Earth sufficiently uniform and featureless initially, but as the Earth has a bulge at the equator due to its axial rotation, removing that spin would result in the Earth returning to a shape that is more spherical than ellipsoidal. This would cause herculean-scale orogenic movements around the planet as it tried to reform its geodesic shape over time. The tectonic readjustments would take longer to unfold than the redistribution of the water on Earth would. In real life, the oceans, which are also subjected to the centrifugal force of the rotation, are elevated at the equator by about 8km where the gravitational force is strongest. This means that, on a non-rotating Earth, the oceans would migrate to the poles, causing land in the equatorial region to emerge. This would eventually result in a huge belt of equatorial mega-continent and two large circumpolar oceans that submerged Canada, the northern Eurasian continent up to the Mediterranean, and the tip of South America.
What kind of atmospheric circulation pattern might we expect on an Earth like that? Soon enough, the coldest places on Earth would not be the poles anymore – it would be the anti-solar point of the Earth (the ‘night’ side where insolation is zero) that is the coldest. This is because we have assumed that the Earth would keep revolving around the Sun as usual, which means that the Earth would now experience 6 months of day followed by 6 months of night. On the sub-solar side (the ‘day’ side, where there is maximum insolation) of the planet, as solar radiation is 1.4kW/m2, each square meter of land would receive more solar energy than a commercial-grade microwave on ‘high’ by midsummer (or in our case now: ‘midday’). On the anti-solar side, the temperature would be as low as -40°C (curiously this figure in Celsius also equals itself in Fahrenheit). As clouds don’t form within a cold atmosphere and thus no insulation or preservation of heat may occur. The ‘night’ side of the planet would therefore be frozen.
In this case, we would expect an atmospheric circulation from the sub-solar to the anti-solar point that passed symmetrically around the equator and over the present-day polar regions, resulting in 2 big atmospheric circulation cells, each covering the whole of the northern or the southern hemisphere. The ITCZ would only be found on the ‘day’ side of the planet, as the anti-polar night side would be too cold for any convection column to form. At the actual sub-solar point on the equator on the ‘day’ side, we could expect very little precipitation if any at all despite it being a convergence zone, as the land there would be bare and dry with all the oceans migrated to the polar regions. The temperature gradient between the hot and cold side of the planet would still allow air to circulate. Hot air would rise very quickly (given the immense supply of heat energy) up the atmosphere at the sub-solar equator and, under no influence of the Coriolis force, travel straight to the anti-solar side of the Earth. The cold air from the anti-solar side would subsequently be drawn, passing the twilight/dawn zones (which includes the poles) midway, into the ‘day’ side of the planet. In these twilight/dawn zones, just as you think the temperature would be more temperate, the wind speed and strength would be the most horrendous on Earth as the temperature gradient would be the steepest there.
As for oceanic circulation, there would be none on the anti-solar side of the Earth as the seas there would be frozen. Thermohaline stratification and latitudinal temperature gradient would still allow the movement of liquid water, but without deflection by the Coriolis force, the oceans would just circulate back and forth the poles and where they bordered the land around mid-latitudes.
How about other geophysical rotations within the planetary system? The Earth’s inner core rotates slightly faster that the outer core to generate the magnetic field that shields us from cosmic radiation including the solar winds. These rotations would also come to a stop after the Earth had ceased to spin, leaving the Earth exposed to the bombardment of charged electromagnetic particles.
That second half of the story as told above involves virtually no life, as the first few incidents would have wiped it all out except for maybe the tardigrade (a.k.a. the water bear). What if we allowed the Earth to slow down gradually to give life enough time to adapt? As the Earth would still eventually come to a standstill, life on Earth would need to find somewhere habitable on the planet. The thin strip of land along the twilight zone between the ‘day’ and the ‘night’ side sounds a good candidate, where the Sun would always appear just above or just below the horizon. The temperature would be moderate, but as discussed before, the wind pattern would be very angry there due to the steep pressure gradient. Even if life could put up with this, there would still need to be constant nomadic migration of the whole civilisation to chase after this line of transition as the Earth travelled along its orbit around the Sun. On the other hand, a mobile base on water near the poles might be a better idea, as a trip around the circumference of the planet there is shorter. In fact, the Inuit people (had they not been flooded by the new polar oceans) might probably never have noticed that the Earth’s rotation had stopped. Equally, aquatic life would be just about fine.
In reality, the Earth’s axial rotation is indeed slowing down. This is due to the diminishing torqueing of the Moon and the Sun upon the Earth, but it is all happening at a rate by which it would take 18.5 billion years for the Earth to have a day as long as a year. The rotation period would eventually slow to 1 rotation every 365 days where the Earth becomes ‘sun synchronous’. This is not a situation of ‘stopped’ rotation, but it is as far as the laws of physics would allow the Earth to get.
In the meantime, the Sun is also moving along its lifespan. In approximately 5 billion years, the Sun will begin the helium-burning process, turning into a red giant star which would eat up all inner planets within the Solar System. So, the Earth might quite likely be swallowed up already before it had the time to get disastrously slow in its rotation – it would die a different, quicker death.
By Eswyn Chen
DISCLAIMER: THE VIEWS EXPRESSED IN THIS ARTICLE ARE THOSE OF THE AUTHOR ONLY AND DO NOT REPRESENT THE VIEWS OR OPINIONS OF COMPASS MAGAZINE AS A WHOLE OR THE UNIVERSITY OF CAMBRIDGE DEPARTMENT OF GEOGRAPHY.