The Siderian Period (; , meaning "iron") is the first
geologic period
The geologic time scale or geological time scale (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochronolo ...
in the
Paleoproterozoic
The Paleoproterozoic Era (also spelled Palaeoproterozoic) is the first of the three sub-divisions ( eras) of the Proterozoic eon, and also the longest era of the Earth's geological history, spanning from (2.5–1.6 Ga). It is further sub ...
Era and lasted from
Ma to Ma. Instead of being based on
stratigraphy
Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks.
Stratigraphy has three related subfields: lithost ...
, these dates are defined
chronometrically.
The deposition of
banded iron formation
Banded iron formations (BIFs; also called banded ironstone formations) are distinctive units of sedimentary rock consisting of alternating layers of iron oxides and iron-poor chert. They can be up to several hundred meters in thickness and e ...
s peaked early in this period. These iron-rich formations were formed as anaerobic
cyanobacteria
Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...
produced waste
oxygen
Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
that combined with
iron
Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
, forming
magnetite
Magnetite is a mineral and one of the main iron ores, with the chemical formula . It is one of the iron oxide, oxides of iron, and is ferrimagnetism, ferrimagnetic; it is attracted to a magnet and can be magnetization, magnetized to become a ...
(Fe
3O
4, an
iron oxide
An iron oxide is a chemical compound composed of iron and oxygen. Several iron oxides are recognized. Often they are non-stoichiometric. Ferric oxyhydroxides are a related class of compounds, perhaps the best known of which is rust.
Iron ...
). This process removed iron from the Earth's oceans, presumably turning greenish seas clear. Eventually, with no remaining iron in the oceans to serve as an oxygen sink, the process allowed the buildup of an oxygen-rich
atmosphere
An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...
. This second, follow-on event is known as the
oxygen catastrophe, which some geologists believe triggered the
Huronian glaciation.
Since the time period from 2,420 Ma to 2,250 Ma is well-defined by the lower edge of iron-deposition layers, an alternative period named the Oxygenian, based on stratigraphy instead of chronometry, was suggested in 2012 in a geological timescale review.
References
*
"The Siderian" Dinosaurfact.net. Retrieved May 24, 2015.
Paleoproterozoic
Geological periods
Proterozoic geochronology
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