Main Page

Welcome to the explain xkcd wiki!
We have an explanation for all 3134 xkcd comics, and only 47 (1.5%) are incomplete. Help us finish them!

 Go to this explanation

Latest comic

Coastline Similarity

|< < Prev #3132 (August 22, 2025)

Title text: Hey! A bunch of the early Cretaceous fossils on each coast seem to have been plagiarized, too!

|< < Prev Random Explanation

Explanation

This comic depicts a classroom, likely relating to geography, geology or history, in which the teacher (Miss Lenhart) is discussing the similar coastlines of Africa and South America, and the way that modern understanding has revealed the cause, before being interrupted by one of her students who is guessing that one coastline plagiarized the other. She continues by revealing that it was continental drift that explained the similarity.

Of course, coastlines are inanimate objects, and have no concept of plagiarism, let alone know how to perform it.^{[citation needed]}

Continental drift is the widely accepted theory that Earth's continents were once all connected, and have been moving relative to each other due to plate tectonics. One of the clues that actually led to this discovery was that the shapes of the coastlines of South America and Africa that are separated by the Atlantic Ocean are similar. The similarity is much greater for the submerged continental shelves than for the visible coastlines; they're like adjacent pieces of a jigsaw puzzle.

The title text continues the joke about plagiarism. Additional corroborating evidence of continental drift is that there are similar species of plant and animal fossils on the two sides of the Atlantic, dating to the time when they were connected. Cueball thinks that the progenitors of these species also plagiarized each other.

The theory of continental drift was originally proposed by Alfred Wegener in 1912, based on such fossil evidence and other geological features common to the two continental borders, in addition to the similarities in shoreline shapes. It's significant to the history of science as a general subject, as a proposal that was originally met with strong opposition (not to mention mockery) but eventually became accepted by almost everyone. Modern cranks and crackpots sometimes point to it in support of their own implausible "theories", as though universal rejection of a "theory" by all of the experts somehow proves that it will someday be accepted and its originator proven right all along. In fact, Wegener's original theory did have a serious flaw, in that it lacked a plausible mechanism, though it was otherwise correct. Modern cranks' "theories" generally lack both plausible mechanisms and good analysis of supporting evidence. ("Yes, they laughed at Galileo... but they also laughed at Bozo the Clown.")

Transcript

[Miss Lenhart is holding a pointer pointing to a wall map. The map shows South America and Africa, with the east coast of South America and the southwest coast of Africa highlighted in red.]

Miss Lenhart: People had long noticed that South America and Africa had similarly-shaped coastlines.

[A side view of the classroom. Jill and Cueball are sitting at school desks, looking at Miss Lenhart. The wall map is visible behind Miss Lenhart.]

Miss Lenhart: In the 20^th century, geologists finally found the explanation:

[The same scene, with Cueball having his hands on his face.]

Cueball: Plagiaris--

Miss Lenhart: Continental drift.

Cueball: Oh.

---

        View comic discussion

New here?

Last 7 days (Top 10)

Rank Score Pages Changes Username 1 43 33 56 FaviFake 2 27 16 49 Tiny Man in a Box 3 22 19 22 CalibansCreations 4 22 18 22 TheusafBOT 5 19 12 25 Mathmaster 6 16 8 25 BunsenH 7 14 9 15 管委会篝火无法解放军“赐额“你去呢管理哦法？ 8 12 5 16 Barry Margolin 9 11 6 12 Aprilfoolsupdate!

Lots of people contribute to make this wiki a success. Many of the recent contributors above have just joined. You can do it too! Create your account here.

You can read a brief introduction about this wiki at explain xkcd. Feel free to create an account and contribute to the wiki! We need explanations for xkcd comics, characters, What If? articles, and everything in between. If it is referenced in an xkcd comic, it should be here.

• If you're new to wiki editing, see the explain xkcd:Editor FAQ for a specific guidance to this wiki and the more general help on how to edit wiki pages. There's also a handy wikicode cheatsheet.

• Discussion about the wiki itself happens at the Community portal.

• You can browse the comics from the list of all comics or by navigating the category tree at Category:Comics.

• The incomplete explanations are listed here. Feel free to help out by expanding them!

Rules

Don't be a jerk!

There are a lot of comics that don't have set-in-stone explanations; feel free to put multiple interpretations in the wiki page for each comic.

If you want to talk about a specific comic, use its discussion page.

Please only submit material directly related to xkcd and, of course, only submit material that can legally be posted and freely edited. Off-topic or other inappropriate content is subject to removal or modification at admin discretion, and users who repeatedly post such content will be blocked.

If you need assistance from an admin, post a message to the Admin requests board.