Lunonautów, którzy LM Falcon wylądowali na Księżycu , zastanowił głaz z zielonkawym nalotem. Późniejsze analizy pozwoliły ustalić , że próbka zawiera zielone kuliste szklane mikrostruktury magmy powstałe w gwałtownych wysokotemperaturowych procesach.
The green hue captivated Jim Irwin, whose Irish descent and birthday on St. Patrick’s Day—and the fact that he had stowed some shamrocks in the lunar module—made this a special find. At first, the two men wondered if their eyes or Sun visors were playing tricks on them, but when it was unpacked a few weeks later in the Lunar Receiving Laboratory (LRL), their initial impressions would be confirmed: It was green, made entirely of minuscule spheres of glass, tiny droplets of magma spewed from a fissure by a “fire fountain.” In time, it and other samples would contribute to making Apollo 15 one of the greatest voyages of discovery ever undertaken in human history.
Wyróżniająca się biała skała zainteresowała księżycowych spacerowiczów. Skała należała do plagioklazów czyli do minerałów skaleniowych zawierających lżejsze minerały. Jest to skład mineralny typowy dla skal magmowych.
Uznano, że skład mineralny odpowiada pierwotnej skorupie Księżyca.
W procesie formowania się Księżyca cięższe składniki minerałów jak żelazo czy kryształy z dużą zawartością magnezu
wędrowały w głąb Księżyca, a lżejsze wypływały na górę. Geolodzy przyjęli koncepcję , że w bardzo wczesnym okresie życia Księżyca cała zewnętrzna powierzchnia składała się z płynnych skał. Później w procesie stygnięcia nastąpił proces krystalizacji minerałów.
Próbka oznaczona została numerem 15415. Później nazwano ją “The Genesis Rock” (kamień Genezis). Uznano ją za fragment skorupy pochodzącej z najwcześniejszego okresu ewolucji Księżyca sprzed około 4,1 mld lat.
Najstarsze zidentyfikowane na Ziemi skały są młodsze o około 1,5 mld lat.
Jeśli na Księżycu można znaleźć skały starsze od próbki dostarczonej przez załogę Apollo 15 , to powinny być one niewiele starsze, bo Układ Słoneczny zaczął się tworzyć kilka setek milionów lat wcześniej.
“It was lifted up on a pedestal,” Irwin wrote. “The base was a dirty old rock covered with lots of dust that sat there by itself, almost like an outstretched hand. Sitting on top of it was a white rock almost free of dust. From four feet away I could see unique long crystals with parallel lines, forming striations.” Scott used tongs to pick it up and held it close to his visor to inspect it. The rock was about the same size as his fist and even as he lifted it, some of its dusty coating crumbled away … and he saw large, white crystals.
The rock was almost entirely “plagioclase”—an important tectosilicate feldspar mineral used by petrologists on Earth to help determine the composition, origin, and evolution of igneous rocks—and from their expeditions into the hills of the San Gabriels, Scott recognized it as “anorthosite,” which is the purest form of plagioclase. For some time, lunar geologists had suspected that anorthosite formed the Moon’s original, primordial crust; indeed, data from the unmanned Surveyor 7 lander had suggested its presence in the ejecta of the crater Tycho, and tiny fragments of it had actually been found in samples from both Apollo 11’s landing site at Tranquility Base and Apollo 12’s site in the Ocean of Storms.
“Explaining why most of the Moon’s crust should be composed of anorthosite,” wrote Andrew Chaikin in A Man on the Moon, “led some geologists to an extraordinary scenario. Within the infant satellite, they proposed, there was so much heat that the entire outer shell became an ocean of molten rock. As this ‘magma ocean’ cooled, minerals crystallized. The heavier species, including the iron- and magnesium-rich crystals, sank to the bottom. The lighter crystals, specifically, the mineral [aluminium-rich] plagioclase floated to the top.”
Recognizing the find as probably a piece of the Moon’s primordial crust, Scott could hardly contain his enthusiasm. “Guess what we just found!” he radioed. “I think we just found what we came for!”
After briefly describing the rock’s appearance, Scott placed it into a sample bag by itself. It would be labeled as sample number 15415, but a keen journalist, inspired by the term “petrogenesis”—the study of the origin of igneous rocks—would later offer it a far loftier title: “The Genesis Rock,” a sample of the original lunar crust, coming from one of the earliest epochs of the Moon’s history, some 4.1 billion years ago. This date was reached by geologists at the University of New York at Stony Brook and proved to be almost 1.5 billion years older than the oldest rocks found on Earth. If the Moon was any older than that, noted Chaikin, it wasn’t much older; the Solar System itself was thought to have formed only a few hundred million years earlier.
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