Literature

The Archean-Paleoproterozoic transition (dated ca. 2500-2000 Ma) is commonly associated with the establishment of an oxygen-rich atmosphere and the emergence of an aerobic biosphere. The paper below considers rocks at the very beginning of this period and finds in oil-bearing fluid inclusions abundant evidence for photosynthesising eukaryotes. Some have claimed evidences back to 3700 Ma, but this represents the minority. However, this paper will make it easier to defend the claim that photosynthesis is found early in the Archaean. The gradualistic evolutionary story does not fit these data.

Biomarkers from Huronian oil-bearing fluid inclusions: An uncontaminated record of life before the Great Oxidation Event.
Adriana Dutkiewicz, Herbert Volk, Simon C. George, John Ridley and Roger Buick
Geology: 2006, Vol. 34, No. 6, pp. 437-440.

ABSTRACT: We report detailed molecular geochemistry of oil-bearing fluid inclusions from a ca. 2.45 Ga fluvial metaconglomerate of the Matinenda Formation at Elliot Lake, Canada. The oil, most likely derived from the conformably overlying McKim Formation, was trapped in quartz and feldspar during diagenesis and early metamorphism of the host rock, probably before ca. 2.2 Ga. The presence of abundant biomarkers for cyanobacteria and eukaryotes derived from and trapped in rocks deposited before the Great Oxidation Event is consistent with an earlier evolution of oxygenic photosynthesis than previously thought and suggests that some aquatic settings had become sufficiently oxygenated for sterol biosynthesis by this time. It also implies that eukaryotes survived several extreme climatic events, including the Paleoproterozoic "snowball Earth" glaciations. The extraction of biomarker molecules from Paleoproterozoic oil-bearing fluid inclusions thus establishes a new method, using low detection limits and system blank levels, to trace evolution of life through Earth's early history that avoids the potential contamination problems affecting shale-hosted hydrocarbons.

C. G. Kurland and colleagues sever the link between eukaryotes and prokaryotes in this recent article in Science. Their title refers to the "Irreducible Nature of Eukaryote Cells". The logic of their argument confirms this: the structures and the genetics of eukaryotes mean that an evolutionary pathway from prokaryotes must be rejected. However, they do not again use the word "irreducible" in their paper. What is clear is that the "simple" pathway that the textbooks have proclaimed for years must now be abandoned.

Genomics and the Irreducible Nature of Eukaryote Cells
C. G. Kurland, L. J. Collins, and D. Penny Science 312, 19 May 2006: 1011-1014.

Abstract: Large-scale comparative genomics in harness with proteomics has substantiated fundamental features of eukaryote cellular evolution. The evolutionary trajectory of modern eukaryotes is distinct from that of prokaryotes. Data from many sources give no direct evidence that eukaryotes evolved by genome fusion between archaea and bacteria. Comparative genomics shows that, under certain ecological settings, sequence loss and cellular simplification are common modes of evolution. Subcellular architecture of eukaryote cells is in part a physical-chemical consequence of molecular crowding; subcellular compartmentation with specialized proteomes is required for the efficient functioning of proteins.

Comparative genomics and proteomics have strengthened the view that modern eukaryote and prokaryote cells have long followed separate evolutionary trajectories. Because their cells appear simpler, prokaryotes have traditionally been considered ancestors of eukaryotes (1*4). Nevertheless, comparative genomics has confirmed a lesson from paleontology: Evolution does not proceed monotonically from the simpler to the more complex (5*9). Here, we review recent data from proteomics and genome sequences suggesting that eukaryotes are a unique primordial lineage.

Mitochondria, mitosomes, and hydrogenosomes are a related family of organelles that distinguish eukaryotes from all prokaryotes (10). Recent analyses also suggest that early eukaryotes had many introns (11, 12), and RNAs and proteins found in modern spliceosomes (13). Indeed, it seems that life-history parameters affect intron numbers (14, 15). In addition, "molecular crowding" is now recognized as an important physical-chemical factor contributing to the compartmentation of even the earliest eukaryote cells (16, 17).

Nuclei, nucleoli, Golgi apparatus, centrioles, and endoplasmic reticulum are examples of cellular signature structures (CSSs) that distinguish eukaryote cells from archaea and bacteria. Comparative genomics, aided by proteomics of CSSs such as the mitochondria (18, 19), nucleoli (20, 21), and spliceosomes (13, 22), reveals hundreds of proteins with no orthologs evident in the genomes of prokaryotes; these are the eukaryotic signature proteins (ESPs) (23, 24). The many ESPs within the subcellular structures of eukaryote cells provide landmarks to track the trajectory of eukaryote genomes from their origins. In contrast, hypotheses that attribute eukaryote origins to genome fusion between archaea and bacteria (25*30) are surprisingly uninformative about the emergence of the cellular and genomic signatures of eukaryotes (CSSs and ESPs). The failure of genome fusion to directly explain any characteristic feature of the eukaryote cell is a critical starting point for studying eukaryote origins.