Jun. 03, 2014

Picture of the Week: The Eye of the Sahara

by Chau Tu

Click to enlarge images
A massive circular rock formation marks the desert in Mauritania like a target—it’s the “Eye of the Sahara.” Easier seen from above than from the ground, the Richat Structure (or Guelb er Richat), as it’s formally known, has long been a landmark for space crews returning to earth, indicating that they’d soon be approaching their landing pad in Florida.
Measuring about 25 miles in diameter, the structure was once thought to be the result of a meteorite impact. Further geological research, however, has disproved that theory—there isn’t enough evidence of melted rock at the site, which would normally be present after such an event, according to Michel Jébrak, a professor at the University of Quebec in Montreal who specializes in mineral resources and who’s done multiple studies on the Richat. Instead, the structure most likely formed as the supercontinent Pangaea broke up and gave way to the Atlantic Ocean about 100 million years ago. 
As the ocean opened, an intrusion of magma slowly pushed up from earth’s mantle to the crust, Jébrak explains, which had a doming effect that gave the Richat its circular shape. Several concentric ridges, sculpted by erosion, make the structure difficult to traverse. “It's like a labyrinth,” says Jébrak.
Aside from its prominence in the landscape, the Richat is also extraordinary for the collection of igneous rocks that formed there at varying depths. Four types can be found today: kimberlites, which occur at about 125 miles below the earth’s surface and sometimes contain diamonds; carbonatites, which come from about 30 miles below, are very scarce, and may contain rare earth elements, according to Jébrak; black basalts and basalt-like gabbros; and rhyolites, rich with silica.
Jébrak suggests that there may be a possible Richat “footprint” in other parts of the world—dust or rocks from the time of the Richat’s intrusion could have been picked up by the Saharan wind and carried to distances as far as Israel. Indeed, rocks that formed during a similar doming process at Yellowstone National Park in Wyoming have traveled as far as Montreal by wind. (“So it’s a funny story [that] I crossed the Atlantic from Montreal to Mauritania, just to find the kind of rocks exactly similar to the ones that are in the middle of Montreal,” Jébrak laughs.)
Jébrak says he’s eager to return to Mauritania and do more research on the Richat’s rocks and origins, but has lately been restricted by warnings of terrorist presence in the region.
About Chau Tu

Chau is SciFri's web producer. She spends a lot of her time drinking coffee, seeking out street art, listening to music, and defending Los Angeles. Follow her @chaubtu

The views expressed are those of the author and are not necessarily those of Science Friday.
EVAL ERROR: Entity: line 1: parser error : Space required after the Public Identifier

Entity: line 1: parser error : SystemLiteral " or ' expected

Entity: line 1: parser error : SYSTEM or PUBLIC, the URI is missing


line 1: package tmpevalpackage;
line 2: sub doEval { 
line 3: 	my($parent);
line 4: 	
line 5: 	if($LayoutManager::url_resolved_values{'SEGMENT.nickname'}) {
line 6: 		$parent = $LayoutManager::url_resolved_values{'SEGMENT.nickname'};
line 7: 	}
line 8: 	elsif($LayoutManager::url_resolved_values{'VIDEO.nickname'}) {
line 9: 		$parent = $LayoutManager::url_resolved_values{'VIDEO.nickname'};
line 10: 	}
line 11: 	elsif($LayoutManager::url_resolved_values{'DOCUMENT.nickname'}) {
line 12: 		$parent = $LayoutManager::url_resolved_values{'DOCUMENT.nickname'}
line 13: 	}
line 14: 	
line 15: 	if($parent) {
line 16: 		my(@books) = &Database::SelectClause('BOOK',"parent = $parent");
line 17: 		if(!@books) {
line 18: 			$parent = '';
line 19: 		}
line 20: 	}
line 21: 	
line 22: 	if(!$parent) {
line 23: 		my(@sel) = &Database::SelectClause('GLOBAL','record all ""');
line 24: 		if(@sel) {
line 25: 			$parent = 'GLOBAL.' . $sel[0];
line 26: 		}
line 27: 			$main::ENV{'reading_header'} = "FEATURED READING";
line 28: 	}
line 29: 	
line 30: 	 = '';
line 31: 	
line 32: 	if($parent) {
line 33: 		my(@books) = &Database::SelectClause('BOOK',"parent = $parent");
line 34: 		0 = 0;
line 35: 		my $dots;
line 36: 		foreach(@books) {
line 37: 			my(%data);
line 38: 			&Database::GetRow($_,'BOOK',\%data);
line 39: 			my($status,$title,$author,$url,$image,$width,$height) = &SciFri::Schema::getAmazonItem($data{'isbn'});
line 40: 			if($data{'title'}) {
line 41: 				$title = $data{'title'};
line 42: 			}
line 43: 			if($data{'author'}) {
line 44: 				$author = $data{'author'};
line 45: 			}
line 46: 			if($status eq 'ok') {
line 47: 				 .= "<div class=\"box-2x1-item box-slide\" data-href=\"$url\">";
line 48: 				 .= "	<div class=\"box-2x1-item-photo\">";
line 49: 				 .= "		<div class=\"image-wrapper\" data-jsclass=\"imageWrapper\" data-align=\"right\">";
line 50: 				 .= "			<img src=\"$image\" data-width=\"$width\" data-height=\"$height\">";
line 51: 				 .= "		</div>";
line 52: 				 .= "	</div>";
line 53: 				 .= "	<h4>$title</h4>";
line 54: 				if($author) {
line 55: 					 .= "	<p>by $author</p>";
line 56: 				}
line 57: 				 .= "	<div class=\"box-2x1-more-button\"><a href=\"$url\"><img src=\"/images/v1/icon_text_more_white.png\" width=47 height=15 border=0></a></div>";
line 58: 				 .= "</div>";
line 59: 				++0;
line 60: 			}
line 61: 		}
line 62: 	}
line 63: 	if($parent eq "GLOBAL.1") { $main::ENV{'reading_header'} = "FEATURED READING"; }
line 64: 	else { $main::ENV{'reading_header'} = "RELATED READING"; }
line 65:  };
line 66: &doEval();
line 67: 1;

Science Friday® is produced by the Science Friday Initiative, a 501(c)(3) nonprofit organization.

Science Friday® and SciFri® are registered service marks of Science Friday, Inc. Site design by Pentagram; engineering by Mediapolis.