The Earth sits comfortably in its orbit tilted on its axis at 23 degrees. Knock the planet over - and it wouldn't be the Earth as you know it.
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00:00 The Earth sits comfortably in its orbit,
00:07 tilted on its axis at 23°.
00:10 Knock the planet over,
00:11 and it wouldn't be the Earth as you know it.
00:14 How can a slight change in its actual tilt
00:16 make the planet uninhabitable?
00:19 This is WHAT IF,
00:21 and here's what would happen
00:22 if the Earth's axis was tilted by 90°.
00:27 Only two planets in the Solar System lie on their sides,
00:30 Uranus and the dwarf planet Pluto.
00:33 Now, if something took the Earth off its stand,
00:36 the blue planet would have no chance
00:38 of developing any complex life on its surface.
00:41 But let's start at the beginning.
00:44 This actual tilt, or obliquity,
00:46 is what drives the seasons here on Earth.
00:49 Before the collision that created the Moon,
00:51 the Earth's axis was slowly wobbling around
00:54 somewhere between 0° and 85°.
00:57 Then, our newly formed Moon stabilized it.
01:01 But if that collision happened at a different time,
01:04 things would have turned out very different here on Earth.
01:08 It would be a strange new world.
01:10 As the Earth made its way through orbit,
01:12 its poles would be pointing straight towards the Sun.
01:15 One hemisphere would be shrouded in darkness
01:17 for six months straight,
01:19 while the other would be getting cooked
01:21 by the blazing sunlight.
01:23 One day on Earth would last a whole year.
01:27 At the North Pole,
01:28 the daytime temperatures would rise to a broiling 50°C (107°F).
01:33 A day at the South Pole would be even worse.
01:36 Because the South Pole would be located
01:38 away from climate-controlling ocean currents,
01:40 it would heat up to an almost boiling 80°C (107°F).
01:44 The poles would soak up so much heat from the Sun
01:47 that they wouldn't even freeze
01:48 during the six-month-long night.
01:51 You wouldn't recognize the steaming equatorial tropics.
01:54 With a 90° axial tilt,
01:56 part of the equator would stay encased in ice all year round.
02:01 At some point in this Earth's existence,
02:04 our continents would get clumped together
02:06 around one of the poles.
02:08 Inland temperatures in the daytime would get truly hellish,
02:11 reaching the boiling temperature of water.
02:14 Clouds could help the situation
02:16 and not let all the water vapor off the planet.
02:18 But you wouldn't know.
02:19 You wouldn't stick around that long.
02:21 In this scorching heat,
02:22 the best-case scenario
02:24 would see just a few kinds of bacteria survive.
02:27 Those bacteria might evolve into more complex life forms,
02:30 but they wouldn't be anywhere close
02:32 to how complex we turned out to be.
02:34 The reason would be a lack of oxygen.
02:37 Green plants would be having a hard time surviving
02:39 during the six months of complete darkness.
02:42 They'd drop their seeds at nightfall
02:43 to grow after sunrise.
02:45 But in these conditions,
02:46 would they even have evolved in the first place?
02:50 Interestingly enough,
02:51 if the Earth was 60 million km further away from the Sun,
02:55 a 90° axial tilt wouldn't be so bad.
02:58 The temperatures at the poles
03:00 would never raise above 46°C during the day.
03:03 The coldest it would get at night would be 3°C.
03:06 The only place covered with ice would be the highest mountains.
03:10 So you see,
03:11 simply orbiting a star in the habitable zone
03:14 doesn't mean that a planet is actually capable of sustaining life.
03:18 We're the lucky ones living here on Earth.
03:20 Maybe one day,
03:21 we'll discover another exoplanet just like our home.
03:24 But that's a story for another WHAT IF.
03:29 (dramatic music)
03:31 [MUSIC PLAYING]
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