Reconstructed ancestral enzymes suggest long-term cooling of Earth’s photic zone since the Archean
Open Access
- 17 April 2017
- journal article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences of the United States of America
- Vol. 114 (18), 4619-4624
- https://doi.org/10.1073/pnas.1702729114
Abstract
Paleotemperatures inferred from the isotopic compositions (δ18O and δ30Si) of marine cherts suggest that Earth’s oceans cooled from 70 ± 15 °C in the Archean to the present ∼15 °C. This interpretation, however, has been subject to question due to uncertainties regarding oceanic isotopic compositions, diagenetic or metamorphic resetting of the isotopic record, and depositional environments. Analyses of the thermostability of reconstructed ancestral enzymes provide an independent method by which to assess the temperature history inferred from the isotopic evidence. Although previous studies have demonstrated extreme thermostability in reconstructed archaeal and bacterial proteins compatible with a hot early Earth, taxa investigated may have inhabited local thermal environments that differed significantly from average surface conditions. We here present thermostability measurements of reconstructed ancestral enzymatically active nucleoside diphosphate kinases (NDKs) derived from light-requiring prokaryotic and eukaryotic phototrophs having widely separated fossil-based divergence ages. The ancestral environmental temperatures thereby determined for these photic-zone organisms––shown in modern taxa to correlate strongly with NDK thermostability––are inferred to reflect ancient surface-environment paleotemperatures. Our results suggest that Earth's surface temperature decreased over geological time from ∼65–80 °C in the Archean, a finding consistent both with previous isotope-based and protein reconstruction-based interpretations. Interdisciplinary studies such as those reported here integrating genomic, geologic, and paleontologic data hold promise for providing new insight into the coevolution of life and environment over Earth history.Keywords
This publication has 43 references indexed in Scilit:
- The SILVA ribosomal RNA gene database project: improved data processing and web-based toolsNucleic Acids Research, 2012
- Robustness of Ancestral Sequence Reconstruction to Phylogenetic UncertaintyMolecular Biology and Evolution, 2010
- Oxygen and hydrogen isotope evidence for a temperate climate 3.42 billion years agoNature, 2009
- Palaeotemperature trend for Precambrian life inferred from resurrected proteinsNature, 2008
- Paleoclimates, ocean depth, and the oxygen isotopic composition of seawaterEarth and Planetary Science Letters, 2006
- The evolutionary diversification of cyanobacteria: Molecular–phylogenetic and paleontological perspectivesProceedings of the National Academy of Sciences of the United States of America, 2006
- High Archean climatic temperature inferred from oxygen isotope geochemistry of cherts in the 3.5 Ga Swaziland Supergroup, South AfricaGSA Bulletin, 2003
- Early cyanobacterial fossil record: preservation, palaeoenvironments and identificationEuropean Journal of Phycology, 1999
- MesoproterozoicArchaeoellipsoidès: akinetes of heterocystous cyanobacteriaLethaia, 1995
- Oxygen isotope geochemistry of cherts from the Onverwacht Group (3.4 billion years), Transvaal, South Africa, with implications for secular variations in the isotopic composition of chertsEarth and Planetary Science Letters, 1978