Origins Institute, McMaster University, Hamilton, ON L8S 4M1, Canada;
Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada.
Proc Natl Acad Sci U S A. 2017 Oct 24;114(43):11327-11332. doi: 10.1073/pnas.1710339114. Epub 2017 Oct 2.
Before the origin of simple cellular life, the building blocks of RNA (nucleotides) had to form and polymerize in favorable environments on early Earth. At this time, meteorites and interplanetary dust particles delivered organics such as nucleobases (the characteristic molecules of nucleotides) to warm little ponds whose wet-dry cycles promoted rapid polymerization. We build a comprehensive numerical model for the evolution of nucleobases in warm little ponds leading to the emergence of the first nucleotides and RNA. We couple Earth's early evolution with complex prebiotic chemistry in these environments. We find that RNA polymers must have emerged very quickly after the deposition of meteorites (less than a few years). Their constituent nucleobases were primarily meteoritic in origin and not from interplanetary dust particles. Ponds appeared as continents rose out of the early global ocean, but this increasing availability of "targets" for meteorites was offset by declining meteorite bombardment rates. Moreover, the rapid losses of nucleobases to pond seepage during wet periods, and to UV photodissociation during dry periods, mean that the synthesis of nucleotides and their polymerization into RNA occurred in just one to a few wet-dry cycles. Under these conditions, RNA polymers likely appeared before 4.17 billion years ago.
在简单细胞生命出现之前，RNA（核苷酸）的组成部分必须在早期地球上有利的环境中形成和聚合。此时，陨石和星际尘埃颗粒将核苷（核苷酸的特征分子）等有机物输送到温暖的小池塘中，这些小池塘的干湿循环促进了快速聚合。我们构建了一个全面的数值模型，用于研究温暖小池塘中核苷碱基的演化，从而产生第一批核苷酸和 RNA。我们将地球的早期演化与这些环境中的复杂前生物化学联系起来。我们发现，RNA 聚合物必须在陨石沉积后很快出现（不到几年）。它们的组成核苷碱基主要来自陨石，而不是星际尘埃颗粒。随着大陆从早期的全球海洋中升起，池塘出现了，但陨石的撞击率下降抵消了这种“目标”可用性的增加。此外，核苷碱基在湿期通过池塘渗漏和在干期通过紫外线光解迅速损失，这意味着核苷酸的合成及其聚合形成 RNA 仅发生在一个或几个干湿循环中。在这些条件下，RNA 聚合物可能在 41.7 亿年前之前出现。
