The second eon (major time period) of Earth's existence, from 3.8 to 2.5 gigayears (Gyr, 109 years) before the present. The earliest geological evidence for life dates to this eon.
banded iron formation (BIF)
A geological formation consisting of layers of oxidized iron (Fe3+) which indicates formation under oxygen-rich conditions.
A newly described microbial isolate that may become accepted as an official species.
The recognition of different forms of life and their placement into different categories.
A tool for identifying organisms, in which a series of yes/no decisions successively narrows down the possible categories of species.
An intimate association between different species in which one partner population grows within the body of another organism.
A region of DNA sequence whose properties indicate that it has been transferred from another genome. Usually comprises a set of genes with shared function, such as pathogenicity or symbiosis support.
The trapping of solar radiation heat in the atmosphere by CO2; a cause of global warming.
A DNA sequence that encodes a product essential for transcription or translation.
The ratio of amounts of two different isotopes of an element. The isotope ratio may serve as a biosignature if the ratio between certain isotopes of a given element is altered by biological activity.
A model of early life in which the central components of intermediary metabolism arose from self-sustaining chemical reactions based on inorganic chemicals.
A microscopic fossil in which calcium carbonate deposits have filled in the form of ancient microbial cells.
The use of DNA or RNA sequence information to measure the time of divergence among different species.
A DNA sequence that encodes a product not essential for transcription or translation but involved in cell functions such as metabolism, stress response, or pathogenicity.
A diagram depicting estimates of the relative amounts of evolutionary divergence among different species.
A measurement of genetic relatedness. The classification of animals based on their genetic relatedness.
A means of quickly identifying microbes in the clinical setting, based on a battery of biochemical tests performed simultaneously on an isolated strain.
A model of early life in which RNA performed all the informational and catalytic roles of today's DNA and proteins.
A ribosomal RNA found in the small subunit of the ribosome. Its gene is often sequenced for phylogenetic comparisons.
A mass of sedimentary layers of limestone produced by a marine microbial community over many years.
A phylogenetic tree showing only the relative distances between different species, without indicating which of these diverged earliest from the common ancestor.