Explain xkcd: It's 'cause you're dumb.
We have no rock formations on Earth older than about 3.5 billion years, as the comic points out, because everything solid from before that time has been subducted down into the Earth's mantle, by tectonic movement. The title text hints at the cooler Moon which stopped re-melting its surface much sooner, so we theoretically could learn something about Earth's history from examining our Moon's surface and makeup. Zircons are a type of mineral found in the Earth's crust, some of which have been estimated to be as old as 4.4 billion years, older than any other mineral.
Anyways, here the Earth is anthropomorphized and actively teases the narrator; first it asks the narrator to draw in closer, as if it's about to tell us a secret, but then it whispers "I'll never tell".
- [Image of the earth from space.]
- Nearly 4.5 billion years ago, Earth had liquid water.
- But all the crust older than 3.5 billion years has been recycled into the mantle by subduction.
- A billion years of the stratigraphic record, the memory of the hills, is forever lost to us.
- What was it like here, four billion years ago?
- What secrets do you have?
- Earth: come closer
- [Zoom in on the Earth.]
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- Earth: i'll never tell.
Zircon --JakubNarebski (talk) 06:58, 3 April 2013 (UTC)
See? THIS is how professionals shred evidence. -- Hkmaly (talk) 09:12, 3 April 2013 (UTC)
I'm more curious if stuff from beginning of earth is still suspended in water somewhere. Think about it, can there really be 100% settlement of materials on the bottom of the ocean? Then again the light from that time is still traveling somewhere, we just need faster then light travel and very good sensor. - 220.127.116.11 20:58, 3 April 2013 (UTC)
Interesting that the Earth's replies come from the Canadian Shield? Also, what with the coquettish tone of the Earth, and the detective story tone of the alt-text, could Randall be referencing the Giant impact hypothesis? --18.104.22.168 23:17, 3 April 2013 (UTC)
The line "I'll never tell" rings in my head from some movie, a little girl repeating it over and over, possibly just from a trailer for the movie. Maybe "Don't Say a Word" (2001) but I'm at work so I don't want to play the trailer.... Did this happen to anyone else? --DanB (talk) 14:14, 4 April 2013 (UTC)
- "I'll never tell" is a song from the famous Once More, with Feeling (Buffy the Vampire Slayer), which may explain why it 'rings' in DanB's head. --GD 22.214.171.124 21:06, 9 April 2013 (UTC)
- I have never heard the song, and yet I still feel the same as DanB does. 126.96.36.199 19:31, 4 December 2013 (UTC)-BK
I'm pretty sure it comes from an old commercial, perhaps for Oil of Olay, where an actress talks about how it keeps her looking young and the the camera pulls in closer until she says "How old am I? I'll never tell." That would also fit the context. --RB
The current explanation isn't an explanation at all, it just restates stuff that's in the comic's transcript. I'd improve it, but the only reason I'm here is because I didn't understand the point. Presumably the last two panels refer to some thing from popular culture. Jeremyp (talk) 11:56, 5 April 2013 (UTC)
"Who am I? I'll never tell" was in the opening voice over of every episode of Gossip Girl. Jackdavinci (talk) 18:26, 5 April 2013 (UTC)
- Except "Gossip Girl" is newer than a lot of other potential references, and we already have the identity of the speaker given as Earth (or the personification thereof). 188.8.131.52 07:27, 6 April 2013 (UTC)