explain xkcd - User contributions [en]

3135: Sea Level

2025-08-30T03:43:54Z

2603:8000:5E00:2913:ED87:72A8:EB65:7C19: /* Transcript */ cat

{{comic
| number = 3135
| date = August 29, 2025
| title = Sea Level
| image = sea_level_2x.png
| imagesize = 321x453px
| noexpand = true
| titletext = They're up there with coral islands, lightning, and caterpillars turning into butterflies.
}}

==Explanation==
{{incomplete|This page was created by A FRIENDLY TIDAL WAVE. Don't remove this notice too soon.}}
In this comic [[Cueball]] is wondering aloud what happened to an island, possibly a {{w|sandbar}} that was visible earlier, but is not anymore. [[Megan]] explains to him that the {{w|tide}} has gone up, and thus the island is underwater. She then tells him about what causes tides, namely the {{w|moon}}, which is large enough and orbits close enough to Earth to gravitationally affect the waters of our oceans, causing them to go up and down daily. Similarly to [[2809: Moon]], Cueball is amazed at the oddity of our planet having a natural satellite large enough to affect our oceans, and Randall seems to be as well, as the caption says that if the moon didn't exist, it would sound extremely outlandish and sci-fi-like.

{{w|Tide|Tides}} on Earth would indeed seem strange and unusual to a visitor from almost anywhere else in the universe, along with other features such as the large expanses of liquid water and the oxygen-rich atmosphere that was created by biological activity (photosynthesis). Not to mention the biological activity. As stated in the comic, tides on Earth are largely the result of a single large moon (the Moon) orbiting the Earth at a relatively short distance. If the Moon were absent, tidal amplitudes would be much less, because the Sun's gravity has much less influence on Earth's liquid water masses than the Moon does. Also, if more than one moon were present, or the moon(s) present were much less massive, or the moon(s) present had more distant orbits, tides would have less amplitude, and, in the case of multiple moons, would have much more complex (and possibly difficult to predict) periodicity.

The title text mentions other outlandish phenomena on Earth, comparing them to tides, including {{w|coral islands}}, islands that build up on top of coral reefs out of coral detritus and other natural materials, {{w|lightning}}, when electrical charges come racing down from thunderclouds in a bright flash of light, and the {{w|metamorphosis}} of {{w|butterflies}}, when caterpillars create a chrysalis and come out as butterflies. Unlike coral islands and metamorphosis, which, so far as humans know, are unique to Earth, lightning has been found elsewhere; within our solar system, it [https://science.nasa.gov/science-research/planetary-science/lightning-across-the-solar-system/ occurs on Jupiter, Saturn, and possibly Mars].

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}

:[Single frame, with Megan and Cueball standing at a coastline, with water and waves visible.]

:Cueball: Hey, where's that big island we were looking at this morning?
:Megan: Oh, it's underwater. The ocean's depth here goes up and down by like ten feet every day.
:Cueball: What?
:Megan: It's because the planet has a big moon orbiting near the surface. It causes weird gravity effects.
:Cueball: '''What???'''

:[Caption below the frame:]
:People here are used to them, but tides are one of the weirdest and most sci-fi elements of life on Earth.

{{comic discussion}}<noinclude>
[[Category: Comics featuring Cueball]]
[[Category: Comics featuring Megan]]
[[Category: Astronomy]]

3135: Sea Level

2025-08-30T03:43:06Z

2603:8000:5E00:2913:ED87:72A8:EB65:7C19: /* Transcript */ ce; add cats