Mysterious abrupt carbon-14 increase in coral contributed by a comet

A large and sudden increase in radiocarbon ( 14 C) around AD 773 are documented in coral skeletons from the South China Sea. The 14 C increased by ~ 15‰ during winter and remain elevated for more than 4 months, then increased and dropped down within two months, forming a spike of 45‰ high in late spring, followed by two smaller spikes. The 14 C anomalies coincide with an historic comet collision with the Earth's atmosphere on 17 January AD 773. Comas are known to have percent-levels of nitrogen by weight and are exposed to cosmic radiation in space. Hence they may be expected to contain highly elevated 14 C/ 12 C ratios, as compared to the Earth's atmosphere. The significant input of 14 C by comets may have contributed to the fluctuation of 14 C in the atmosphere throughout the Earth's history, which should be considered carefully to better constrain the cosmic ray fluctuation.