Editing 1194: Stratigraphic Record

{{comic
| number    = 1194
| date      = April 3, 2013
| title     = Stratigraphic Record
| image     = stratigraphic record.png
| titletext = All we have are these stupid tantalizing zircons and the scars on the face of the Moon.
}}

==Explanation==
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 {{w|Subduction|subducted}} down into the {{w|Mantle (geology)|Earth's mantle}}, by {{w|Plate tectonics|tectonic movement}}. The title text hints at the cooler {{w|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. {{w|Zircon|Zircons}} are a type of mineral found in the {{w|Crust (geology)|Earth’s crust}}, some of which have been estimated to be as old as 4.4 billion years, older than any other mineral.

==Transcript==
:[Image of the Earth in color as seen from far off in space with pitch black around the Earth. Two blocks of text are above and below the Earth in white rectangles:]
: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.

:[Same image of Earth, but now with only the middle of the panel black. Above and below is white sections (without a frame) with text:]
: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?

:[A slimmer panel as the first, with two smaller white rectangles with text above and below:]
:Earth,
:What '''''secrets''''' do you have?

:[Similar panel, but now without the white rectangles. Instead a line comes up from the Earth as it speaks with white text, and in small letters, unlike normal xkcd text:]
:Earth: come closer

:[Zoom in on the Earth so it now fills almost the entire panel from left to right.]

:[Further zoom in on the Earth so now only part of the Earth can be seen in the panel. There is still black above, but not on the other three sides of the panel, which is filled with the Earth. It shows the northern part of the Earth with Alaska, Canada and some of mainland USA with one of the great lakes visible at the top right. The sea ice at the North Pole is also visible as are a small part of Russia near Alaska. Again the Earth speaks as in the first panel:]
:Earth: ''i'll never tell.''

{{comic discussion}}

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[[Category:Geology]]