THEORETICAL CONSTRAINTS ON EARLY EARTH'S ENVIRONMENT

概要

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The only geological evidence for the early Earth is zircon which suggests existence of continental crust and oceans at 4.404 billion years ago. Based on the record of the lunar impact craters, it has been considered that heavy bombardment of small solar system bodies to the Earth-Moon system occurred during the first several hundred million years. There is however another possibility that an intense, but short-term impact event (called the cataclysm) might have occurred at around 3.9 billion years ago, which could have been caused by rapid migration of the giant planets. The atmospheric composition during the early Earth was reducing, irrespective of source of volatiles. This may have been favorable for the prebiotic synthesis of organic materials and so the origin of life. The early Earth might have been globally glaciated because the heavy bombardment produced a large amount of impact ejecta which consumed the atmospheric CO_2 effectively through chemical weathering followed by carbonate precipitation. However, the effects of mantle overturn and large-scale resurfacing on the early Earth's environment remains unknown.
2009-06-01