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The "Mountain or Valley?" illusion makes our brains turn valleys inside out. But inside-out valleys are a real thing, both on Earth and on Mars.

Thanks to Skillshare for sponsoring this video, and to our supporters on https://www.patreon.com/MinuteEarth

Watch: The "Mountain Or Valley?" Illusion by MinutePhysics
https://www.youtube.com/watch?v=V7C318DGB38

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If you want to learn more about this topic, start your googling with these keywords:
Inverted relief: a topographic feature, such as an old riverbed, that has reversed its elevation relative to other features.

Duricrust: a hard mineral crust formed at or near the surface of soil in semiarid regions by the evaporation of groundwater.

Geomorphology: the study of the physical features of the surface of the earth and their relation to its geological structures.

Exhumed paleochannel: a remnant of an inactive river or stream channel that has been either filled or buried by younger sediment, and then subsequently uncovered by erosion.

Erosion: the action of surface processes, including wind and water, that move dirt and rock from their original location to some other place.

Capillary action: the tendency of a liquid in a capillary tube or absorbent material to rise or fall as a result of surface tension.

Mineral precipitation: when dissolved compounds in a solution bond together to form a solid (a simple example is how dissolved sodium and chloride ions come together to form salt as water evaporates)
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Credits (and Twitter handles):
Script Writers: David Goldenberg (@dgoldenberg) & Emily Elert (@eelert)
Video Illustrator: Ever Salazar (@eversalazar)
Video Narrator: Emily Elert (@eelert)
With Contributions From: Henry Reich, Alex Reich, Kate Yoshida, Emily Elert, Peter Reich
Music by: Nathaniel Schroeder: http://www.soundcloud.com/drschroeder

Image Credits: Yardangs and Ridges of the Edge of Aeolis Planum - NASA JPL University of Arizona
https://hirise.lpl.arizona.edu/PSP_006683_1740

Raised Footprints - Alan Light
https://www.flickr.com/photos/....alan_light/590449338
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The inverted relief at the end of the video is at Green River, Utah
https://www.google.com/maps/@3....8.8744077,-110.25588

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References:

Clarke, J., July 2016, personal communication.

Clarke, J. D., & Stoker, C. R. (2011). Concretions in exhumed and inverted channels near Hanksville Utah: implications for Mars. International Journal of Astrobiology, 10(03), 161-175. doi:10.1017/s1473550411000048

Harris, D.R. (1980). Exhumed paleochannels in the Lower Cretaceous Cedar
Mountain formation near Green river. Utah: Brigham Young Univ. Geol.
Stud. 27, 51–66.

Malin, M. C. (2003). Evidence for Persistent Flow and Aqueous Sedimentation on Early Mars. Science, 302(5652), 1931-1934. doi:10.1126/science.1090544

Miller, R. P. (1937). Drainage Lines in Bas-Relief. The Journal of Geology, 45(4), 432-438. doi:10.1086/624550

Pain, C.P & Ollier, C.D. (1996). Regolith stratigraphy: principles and problems. Journal of Australian Geology & Geophysics, 16(3), 197-202.

Pain, C., Clarke, J., & Thomas, M. (2007). Inversion of relief on Mars. Icarus, 190(2), 478-491. doi:10.1016/j.icarus.2007.03.017

Pain, C., July 2016, personal communication.