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The term Paleoatmosphere (or palaeoatmosphere) refers to the atmosphere, particularly of earth, at some unspecified time in the geological past.

The composition of Earth's paleoatmosphere can be inferred today from the study of the abundance of proxy materials such as iron oxides, charcoal and the stomatal density of fossil leaves in geological deposits. Although today's atmosphere is dominated by nitrogen (about 78%) and oxygen (about 21%), the pre-biological atmosphere is thought to have been highly reducing, to have contained virtually no free oxygen, virtually no argon
Argon

Argon is a chemical element designated by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table ....
, which is generated by the radioactive decay of 40K
Potassium

Potassium is a chemical element. It has the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash, hence the name....
, and to have been dominated by nitrogen, carbon dioxide and methane.

Appreciable concentrations of free oxygen were probably not present until after the evolution of photosynthetic bacteria
Bacteria

The Bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals....
, such as the cyanobacteria
Cyanobacteria

Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis....
, or blue-green algae about 2Ga before present.






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The term Paleoatmosphere (or palaeoatmosphere) refers to the atmosphere, particularly of earth, at some unspecified time in the geological past.

The composition of Earth's paleoatmosphere can be inferred today from the study of the abundance of proxy materials such as iron oxides, charcoal and the stomatal density of fossil leaves in geological deposits. Although today's atmosphere is dominated by nitrogen (about 78%) and oxygen (about 21%), the pre-biological atmosphere is thought to have been highly reducing, to have contained virtually no free oxygen, virtually no argon
Argon

Argon is a chemical element designated by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table ....
, which is generated by the radioactive decay of 40K
Potassium

Potassium is a chemical element. It has the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash, hence the name....
, and to have been dominated by nitrogen, carbon dioxide and methane.

Appreciable concentrations of free oxygen were probably not present until after the evolution of photosynthetic bacteria
Bacteria

The Bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals....
, such as the cyanobacteria
Cyanobacteria

Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis....
, or blue-green algae about 2Ga before present. By about 500 M years before present, oxygen concentrations had increased sufficiently to enable the evolution of multicellular animal life. Following the appearance, rapid evolution and radiation of land plants to cover much of the earth's land surface, beginning about 450M years ago, oxygen concentrations reached and later exceeded current values during the early Carboniferous, when atmospheric was drawn down below current concentrations.