text: Melted micrometeorites (cosmic spherules) were first collected from deep-sea sediments during the 1873 to 1876 expedition of HMS Challenger. In 1891, Murray and Renard found "two groups [of micrometeorites]: first, black magnetic spherules, with or without a metallic nucleus; second, brown-coloured spherules resembling chondr(ul)es, with a crystalline structure". In 1883, they suggested that these spherules were extraterrestrial because they were found far from terrestrial particle sources, they did not resemble magnetic spheres produced in furnaces of the time, and their nickel-iron (Fe-Ni) metal cores did not resemble metallic iron found in volcanic rocks. The spherules were most abundant in slowly accumulating sediments, particularly red clays deposited below the carbonate compensation depth, a finding that supported a meteoritic origin. In addition to those spheres with Fe-Ni metal cores, some spherules larger than 300 µm contain a core of elements from the platinum group.
  Since the first collection of HMS Challenger, cosmic spherules have been recovered from ocean sediments using cores, box cores, clamshell grabbers, and magnetic sleds. Among these a magnetic sled, called the "Cosmic Muck Rake", retrieved thousands of cosmic spherules from the top 10 cm of red clays on the Pacific Ocean floor.