There are big uncertainties regarding Earth’s surface temperature during the Archean, as deduced from isotopic
measurements of oxygen in carbonate rocks, with values
ranging from 26 to 85 °C (Knauth and Lowe 2003; Robert
and Chaussidon 2006; De Wit and Furnes 2016). However,
these values may be inaccurate due to our lack of understanding of the average d
18 O of the seawater at that time.
Indeed, the average
18 O concentration in the oceans is
determined by
18 O exchanges with oceanic crustal basalts
during the circulation of seawater in the hydrothermal systems of the ocean ridges. There is no evidence to indicate
that it was within the range of values observed much more
recently. Measurements of the isotopic ratio of oxygen and
silicon in cherts (siliceous rocks) suggest a paleotemperature
of 60–80 °C (Fig. 22.1a). However, these values may be
distorted by the contributions of the hydrothermal systems
lining the oceanic crust at that time. To overcome these
difficulties, new isotopic tools, called the clumped isotopes,
have been developed. A promising paleothermometer, based
not on the relative abundance of one single isotope to
another, but on the abundance ratio of isotopologues with
multiple rare isotopes relative to the expected quantity for a
stochastic distribution of isotopes within a (
13 C
18 O
16 O 2 )
2−
group (Eiler 2007; Bonifacie et al. 2017). The thermodynamic variable measured and noted D 47 is therefore based on
the substitution of carbon and oxygen isotopes within the
carbonate ions, which is a function of the temperature at
which these carbonates formed. Although uncertainties
remain (Daëron et al. 2019), this method does not require
knowledge of the average isotopic composition of the ocean
and can therefore be applied to the oceans of the Archean.
Although the evolution of temperature during the Archean is
up for debate, it remained within a range of values able to
sustain liquid water on the Earth’s surface. This is an
essential condition for the development of life which could
have started as early as 3.77 Ga (Dodd et al. 2017).
Maintaining a temperature conducive to the development
of life on Earth was by no means guaranteed within the
context of the “young Sun”. In fact, the radiation emitted by
a young star is weak, gradually increasing throughout its life.
In the case of the Sun, the solar radiation is estimated to have
been 30% lower 4 Ga ago than it is today, and 20% lower
3 Ga ago. In these radiation conditions, maintaining a temperature that would support the presence of liquid water on
the surface of the globe during the Archean would have been
impossible without a powerful greenhouse effect.
Let’s examine the data to determine the constraints on the
chemical composition of the atmosphere. Precipitation of
sodium bicarbonate in the Archean oceans around 3.3 Ga
argues in favour of a partial CO 2 pressure of between 1.4 and
15% of the atmospheric pressure of the time (Lowe and Tice
2004), and so lower than the estimates by the models.
However, the chemical composition of the Precambrian
atmosphere is the subject of intense debate because a high
partial pressure of CO 2 , necessary to counter the “young
sun” effect, would have strongly acidified precipitations,
causing the pH to fall to about 3.7, and cause a particularly
intense chemical weathering of the rocks, which does not
seem to be the case for the 3.5–3 Ga period (Kasting and
Howard 2006). Another gas, methane, may therefore have
played an important role. In the modern atmosphere, the
residence time of methane is around eight years because it is
quickly oxidized. However, in an atmosphere devoid of
oxygen or at very low partial pressures (<10
−5 bar) as in the
Archean, this residence time is considerably longer. Methane
can thus accumulate in the atmosphere and significantly
increase the greenhouse effect. We know of two sources of
methane at that time: methanogenic organisms and the serpentinization of ultramafic rocks on the ocean floor. Taking
the results of the work of Haqq-Mishra et al. (2008), with
1% methane in the atmosphere, the CO 2 partial pressure
required to maintain the Earth at 30 °C drops to about 10
−3
bar. The contribution of methane to the greenhouse effect is
therefore extremely effective. Even if atmospheric concentrations remain poorly constrained, a CH 4 to CO 2 ratio
greater than 0.2 is impossible (Zerkle et al. 2012).
Traces of several glacial periods, dated between 3.5 and
2.2 Ga, have been discovered in South Africa, Europe,
North America and Australia. The oldest glaciation was
discovered in South Africa within the Barberton Greenstone
Belt. It was dated at about 3.4–3.5 Ga (De Wit and Furnes
2016) and in a latitude band between 20° and 40° (Biggin
et al. 2011). It was followed by another glacial episode at
2.9 Ga discovered in units of the Mozaan geological group
in South Africa (Young et al. 1998). The end of the Archean
and the beginning of the Proterozoic produced the Huron
glaciation, originally discovered in the province of Ontario
in Canada, but identified in South Africa and Australia. It is
actually a succession of three or four glacial events, dated
between 2.45 and 2.2 Ga (Caquineau et al. 2018). One of
these glacial episodes is demonstrated by the presence of
glacial sediment at low latitudes and at low altitude suggesting that the Earth could have been completely frozen at
this time. These glaciations are associated with a major event
in the history of the Earth: the oxygenation of the atmosphere and of the shallow oceans.
The next billion years (between 1.85 and 0.85 Ga) is
often referred to as the ‘boring billion’ due to the apparent
climatic and environmental stability. Indeed, isotopic measurements of carbon (d
13 C) show no major disturbance of
the carbon cycle and the absence of any known glacial traces
during this period suggest (but do not prove) that the Earth’s
climate had stabilized into a hot configuration. This climate
stability ended with the Neoproterozoic. During this time,
the Earth experienced three periods of glaciation: the Sturtian glaciation from 717 to 659 Ma, the Marinoan glaciation
22 Climate Evolution on the Geological Timescale and the Role …
257
measurements of oxygen in carbonate rocks, with values
ranging from 26 to 85 °C (Knauth and Lowe 2003; Robert
and Chaussidon 2006; De Wit and Furnes 2016). However,
these values may be inaccurate due to our lack of understanding of the average d
18 O of the seawater at that time.
Indeed, the average
18 O concentration in the oceans is
determined by
18 O exchanges with oceanic crustal basalts
during the circulation of seawater in the hydrothermal systems of the ocean ridges. There is no evidence to indicate
that it was within the range of values observed much more
recently. Measurements of the isotopic ratio of oxygen and
silicon in cherts (siliceous rocks) suggest a paleotemperature
of 60–80 °C (Fig. 22.1a). However, these values may be
distorted by the contributions of the hydrothermal systems
lining the oceanic crust at that time. To overcome these
difficulties, new isotopic tools, called the clumped isotopes,
have been developed. A promising paleothermometer, based
not on the relative abundance of one single isotope to
another, but on the abundance ratio of isotopologues with
multiple rare isotopes relative to the expected quantity for a
stochastic distribution of isotopes within a (
13 C
18 O
16 O 2 )
2−
group (Eiler 2007; Bonifacie et al. 2017). The thermodynamic variable measured and noted D 47 is therefore based on
the substitution of carbon and oxygen isotopes within the
carbonate ions, which is a function of the temperature at
which these carbonates formed. Although uncertainties
remain (Daëron et al. 2019), this method does not require
knowledge of the average isotopic composition of the ocean
and can therefore be applied to the oceans of the Archean.
Although the evolution of temperature during the Archean is
up for debate, it remained within a range of values able to
sustain liquid water on the Earth’s surface. This is an
essential condition for the development of life which could
have started as early as 3.77 Ga (Dodd et al. 2017).
Maintaining a temperature conducive to the development
of life on Earth was by no means guaranteed within the
context of the “young Sun”. In fact, the radiation emitted by
a young star is weak, gradually increasing throughout its life.
In the case of the Sun, the solar radiation is estimated to have
been 30% lower 4 Ga ago than it is today, and 20% lower
3 Ga ago. In these radiation conditions, maintaining a temperature that would support the presence of liquid water on
the surface of the globe during the Archean would have been
impossible without a powerful greenhouse effect.
Let’s examine the data to determine the constraints on the
chemical composition of the atmosphere. Precipitation of
sodium bicarbonate in the Archean oceans around 3.3 Ga
argues in favour of a partial CO 2 pressure of between 1.4 and
15% of the atmospheric pressure of the time (Lowe and Tice
2004), and so lower than the estimates by the models.
However, the chemical composition of the Precambrian
atmosphere is the subject of intense debate because a high
partial pressure of CO 2 , necessary to counter the “young
sun” effect, would have strongly acidified precipitations,
causing the pH to fall to about 3.7, and cause a particularly
intense chemical weathering of the rocks, which does not
seem to be the case for the 3.5–3 Ga period (Kasting and
Howard 2006). Another gas, methane, may therefore have
played an important role. In the modern atmosphere, the
residence time of methane is around eight years because it is
quickly oxidized. However, in an atmosphere devoid of
oxygen or at very low partial pressures (<10
−5 bar) as in the
Archean, this residence time is considerably longer. Methane
can thus accumulate in the atmosphere and significantly
increase the greenhouse effect. We know of two sources of
methane at that time: methanogenic organisms and the serpentinization of ultramafic rocks on the ocean floor. Taking
the results of the work of Haqq-Mishra et al. (2008), with
1% methane in the atmosphere, the CO 2 partial pressure
required to maintain the Earth at 30 °C drops to about 10
−3
bar. The contribution of methane to the greenhouse effect is
therefore extremely effective. Even if atmospheric concentrations remain poorly constrained, a CH 4 to CO 2 ratio
greater than 0.2 is impossible (Zerkle et al. 2012).
Traces of several glacial periods, dated between 3.5 and
2.2 Ga, have been discovered in South Africa, Europe,
North America and Australia. The oldest glaciation was
discovered in South Africa within the Barberton Greenstone
Belt. It was dated at about 3.4–3.5 Ga (De Wit and Furnes
2016) and in a latitude band between 20° and 40° (Biggin
et al. 2011). It was followed by another glacial episode at
2.9 Ga discovered in units of the Mozaan geological group
in South Africa (Young et al. 1998). The end of the Archean
and the beginning of the Proterozoic produced the Huron
glaciation, originally discovered in the province of Ontario
in Canada, but identified in South Africa and Australia. It is
actually a succession of three or four glacial events, dated
between 2.45 and 2.2 Ga (Caquineau et al. 2018). One of
these glacial episodes is demonstrated by the presence of
glacial sediment at low latitudes and at low altitude suggesting that the Earth could have been completely frozen at
this time. These glaciations are associated with a major event
in the history of the Earth: the oxygenation of the atmosphere and of the shallow oceans.
The next billion years (between 1.85 and 0.85 Ga) is
often referred to as the ‘boring billion’ due to the apparent
climatic and environmental stability. Indeed, isotopic measurements of carbon (d
13 C) show no major disturbance of
the carbon cycle and the absence of any known glacial traces
during this period suggest (but do not prove) that the Earth’s
climate had stabilized into a hot configuration. This climate
stability ended with the Neoproterozoic. During this time,
the Earth experienced three periods of glaciation: the Sturtian glaciation from 717 to 659 Ma, the Marinoan glaciation
22 Climate Evolution on the Geological Timescale and the Role …
257