ISS030-E-254011 (21 April 2012) --- The Ouarkziz Impact Crater is featured in this image photographed by an Expedition 30 crew member on the International Space Station. The Ouarkziz Impact Crater is located in northwestern Algeria close to the border with Morocco. According to scientists, the crater was formed by a meteor impact less than 70 million years ago during the late Cretaceous Period of the Mesozoic Era or "Age of Dinosaurs". Originally called Tindouf, the 3.5-kilometer in diameter impact crater (center) has been heavily eroded since its formation; however its circular morphology is highlighted by exposures of older sedimentary rock layers that form roughly northwest-to-southeast-trending ridgelines to the north and south. From the vantage point of a crew member onboard the space station, the impact crater is clearly visible with a magnifying camera lens. A geologist interpreting this image to build a working geological history of the region would conclude that the Ouarkziz impact crater is younger than the sedimentary rocks, as the rock layers had to be already present for the meteor to hit them. Likewise, a stream channel is visible cutting across the center of the impact structure (center), indicating that the channel formed after the impact had occurred. This Principal of Cross-Cutting Relationships, usually attributed to the famous 19th century geologist Charles Lyell, is a basic logic tool used by geologists to build relative sequence and history of events when investigating a region.
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