EnvSci Q01 W05 QG01

a. Early in the Archean (ancient) eon, about 3.8 billion years ago, the rain of meteors and rock bodies from space ended, allowing our planet's surface to cool and solidify.

b. Water vapor in the atmosphere condensed and fell as rain, creating oceans. These changes created the conditions for geochemical cycling (flow of chemical substances between reservoirs in Earth atmosphere, hydrosphere (water bodies), and lithosphere (the solid part of Earth´s crust).

Early in the Archean (ancient) eon, about 3.8 billion years ago, the rain of meteors and rock bodies from space ended, allowing our planet's surface to cool and solidify.

Water vapor in the atmosphere condensed and fell as rain, creating oceans. These changes created the conditions for geochemical cycling (flow of chemical substances between reservoirs in Earth atmosphere, hydrosphere (water bodies), and lithosphere (the solid part of Earth´s crust).

Weathering rates accelerate and convert an increasing fraction of atmospheric CO2 to calcium carbonate, which is buried on the ocean floor. Atmospheric concentrations of CO2 decline, modifying the greenhouse effect and cooling Earth's surface.

Weathering slows down but volcanic outgassing of CO2 continues, so atmospheric CO2 levels rise and warm the climate.

Weathering rates accelerate and convert an increasing fraction of atmospheric CO2 to calcium carbonate, which is buried on the ocean floor. Atmospheric concentrations of CO2 decline, modifying the greenhouse effect and cooling Earth's surface.

Weathering slows down but volcanic outgassing of CO2 continues, so atmospheric CO2 levels rise and warm the climate.

The sun was about 30 percent dimmer than it is today, so our planet received less solar radiation. Earth's surface should have been well below the freezing point of water, too cold for life to exist, but evidence shows that liquid water was present and that simple life forms appeared as far back as 3.5 billion years ago.

the sun was about 30 percent dimmer than it is today, so our planet received less solar radiation. Earth's surface should have been well below the freezing point of water, too cold for life to exist, but evidence shows that liquid water was present and that simple life forms appeared as far back as 2.5 billion years ago.

Nitrogen, liquid water , methane (CH4), and CO2.

Nitrogen, water vapor, methane (CH4), and CO2.

Volcanoes emitted CO2 as a byproduct of heating within the Earth's crust.

Volcanoes emitted CO2 as a byproduct of industry.

Natural sink, a process that adds excess carbon from atmosphere. This sink involves the weathering of silicate rocks, such as granites and basalts, that make up much of Earth's crust.

Natural sink, a process that removes excess carbon from atmosphere. This sink involves the weathering of silicate rocks, such as granites and basalts, that make up much of Earth's crust.

First, rainfall scrubs CO2 out of the air, producing carbonic acid (H2CO3), a weak acid.

This carbonic acid reacts on contact with silicate rocks to release calcium and other cations and leave behind carbonate and biocarbonate ions dissolved in the water.

Rainfall scrubs CO2 out of the air, producing carbonic acid (H2CO3), a weak acid.

The Carbonic acid reacts on contact with silicate rocks to release calcium and other cations and leave behind carbonate and biocarbonate ions dissolved in the water.

The carbonate and biocarbonate ions dissolved in the water is washed into the oceans by rivers, and then calcium carbonate (CaCO3), also known as limestone, is precipitated in sediments.

Over long time scales, oceanic crust containing limestone sediments is forced downward into Earth's mantle at points where plates collide, a process called subduction. Eventually, the limestone heats up and turns the limestone back into CO2, which travels back up to the surface with magma. Volcanic activity then returns CO2 to the atmosphere.

Over long time scales, oceanic crust containing limestone sediments is forced upward into Earth's mantle at points where plates collide, a process called subduction. Eventually, the limestone heats up and turns the limestone back into CO2, which travels back up to the surface with magma. Volcanic activity then returns CO2 to the atmosphere.

Over long time scales, oceanic crust containing limestone sediments is forced downward into Earth's mantle at points where plates collide, a process called subduction. Eventually, the limestone heats up and turns the limestone back into CO2, which travels back up to the surface with magma. Volcanic activity then returns CO2 to the atmosphere.

The balance between CO2 outgassing from volcanoes and CO2 conversion to calcium carbonate through silicate weathering has kept the Earth's climate stable through most of its history.

The balance between CO2 outgassing from volcanoes and CO2 conversion to wood and oxygen through forest photosysthesis has kept the Earth's climate stable through most of its history.