Melott Adrian L
Department of Physics and Astronomy, University of Kansas , Lawrence, Kansas.
Astrobiology. 2017 Jan;17(1):87-90. doi: 10.1089/ast.2016.1527. Epub 2016 Dec 27.
Major discrepancies have been noted for some time between fossil ages and molecular divergence dates for a variety of taxa. Recently, systematic trends within avian clades have been uncovered. The trends show that the disparity is much larger for mitochondrial DNA than for nuclear DNA, also that it is larger for crown fossil dates than stem fossil dates. It has been argued that this pattern is largely inconsistent with incompleteness of the fossil record as the principal driver of the disparity. A case is presented that, given the expected mutations from a fluctuating background of astrophysical radiation from such sources as supernovae, the rate of molecular clocks is variable and should increase back to a few million years, before returning to the long-term average rate. This is a possible explanation for the disparity. One test of this hypothesis is to look for an acceleration of molecular clocks at 2 to 2.5 Ma due to one or more moderately nearby supernovae known to have happened at that time. Another is to look for reduced disparity in benthic organisms of the deep ocean. In addition, due to the importance of highly penetrating muon irradiation, the disparity should be magnified for megafauna. Key Words: Extreme events in Earth history-Molecular clock-Radiation physics-Evolution. Astrobiology 17, 87-90.
一段时间以来，人们已经注意到各种分类群的化石年龄和分子分歧日期之间存在重大差异。最近，鸟类进化枝内部的系统趋势被发现。这些趋势表明，线粒体DNA的差异比核DNA大得多，而且冠化石日期的差异比干群化石日期大。有人认为，这种模式在很大程度上与化石记录的不完整性不一致，而化石记录的不完整性是差异的主要驱动因素。有人提出，考虑到来自超新星等天体物理辐射波动背景的预期突变，分子钟的速率是可变的，并且在恢复到长期平均速率之前，应该会回升到几百万年。这是对差异的一种可能解释。对这一假设的一个检验是寻找由于当时已知发生的一颗或多颗适度距离的超新星而导致的分子钟在2至250万年前的加速。另一个是寻找深海底栖生物中差异的减少。此外，由于高穿透力的μ子辐射的重要性，巨型动物的差异应该会放大。关键词：地球历史中的极端事件-分子钟-辐射物理学-进化。天体生物学17，87-90。
