Evidence included: zircons hint at early tectonic activity, life.Two analyses of tiny mineral bits that crystallized crys·tal·lize also crys·tal·ize v. crys·tal·lized also crys·tal·ized, crys·tal·liz·ing also crys·tal·iz·ing, crys·tal·liz·es also crys·tal·iz·es v.tr. 1. during the Earth's formative years have provided new insights into the planet's earliest days. One study of mineral inclusions in zircons from the Jack Hills of Western Australia Western Australia, state (1991 pop. 1,409,965), 975,920 sq mi (2,527,633 sq km), Australia, comprising the entire western part of the continent. It is bounded on the N, W, and S by the Indian Ocean. Perth is the capital. hints that the crystals formed at depths of around 25 kilometers and at temperatures of about 700[degrees] Celsius. Those findings, in turn, suggest that plate tectonics plate tectonics, theory that unifies many of the features and characteristics of continental drift and seafloor spreading into a coherent model and has revolutionized geologists' understanding of continents, ocean basins, mountains, and earth history. had already begun on Earth between 4.19 billion and 4.02 billion years ago, less than 600 million years after the planet first coalesced co·a·lesce intr.v. co·a·lesced, co·a·lesc·ing, co·a·lesc·es 1. To grow together; fuse. 2. To come together so as to form one whole; unite: (SN: 1/3/09, p. 10). Another study, this one of the carbon-isotope ratios of microdiamond inclusions in zircons that ranged between 3.05 billion and 4.25 billion years of age, found a much-lower-than-average concentration of the carbon-13 isotope in those inclusions, a possible sign of biological processes (SN: 8/2/08, p. 13). Metabolic processes that take place in an organism's cells, and especially in microorganisms, produce isotopically light carbon. A much-higher-than-average concentration of carbon-12, the lightest of carbon's stable isotopes, often is a sign that the carbon was generated by biologic activity. The ratio of carbon-13 to carbon-12 was far below that found in other diamonds and even in other reservoirs of isotopically light carbon, including carbon-rich meteorites Meteorites See also astronomy. aerolithology the science of aerolites, whether meteoric stones or meteorites. Also called aerolitics. astrolithology the study of meteorites. Also called meteoritics. and interplanetary dust Noun 1. interplanetary dust - microscopic particles in the interplanetary medium interplanetary medium - interplanetary space including forms of energy and gas and dust . If the ratio is indeed a sign of life, it pushes back the presence of life on Earth at least 400 million years. [ILLUSTRATION OMITTED] --Elizabeth Quill, News Editor |
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