Evolution of the Atmosphere

Evolution of our atmosphere

• Original Atmosphere of Hydrogen (H) and Helium (He) lost.

Secondary atmosphere develops

• planetesimal collisions – released volatiles

trapped in grains

Early Atmosphere

VaporMethane (CH4) and Sulfur

Volcanic outgassing

• Carbon dioxide (CO2)

• Sulfur oxides• Water vapor

• Methane (CH4 )

Two keys to the evolution of planetary atmospheres:

• Fate of the water vapor (gaseous, liquid, solid)

• Fate of the Carbon Dioxide (stays in atmosphere vs. dissolves in liquid water)

Condensation of water vapor is crucial

• On this planet it was too cold for water vapor to condense. Hence the atmosphere is all Carbon Dioxide

• On this planet it was too hot for water vapor to condense. Hence the atmosphere is all Carbon Dioxide

On this planet it was just right. The carbon dioxide content of the earth's atmosphere is now all locked

up in rocks.

Precipitation…cools down the planet…water now as a liquid

• Condensation of water vapor produced the earth's oceans– sweeping out the

carbon dioxide and locking it up into rocks

– our atmosphere was mostly nitrogen.

Primitive Oceans born

• CO2 + H2O (liquid) = H2CO3 = Acid rain

Limestone locked up in rocks

• H2CO3+ Ca = CaCO3 (limestone)

Early Earth

• The freshly formed Earth was a pretty rough place,

As comets and meteors slammed in from space.

We'd choke on the gases of that atmosphere,

Other types of rocks formed

• H2CO3 + CaMg (CO3)2 - dolomites

Composition of our atmosphere

What about the nitrogen?

• N2 chemically inert, so it stays in the atmosphere

• N2 cycle develops later

Early Earth-Moon System

• The moon was closer to the Earth

• It exerted a much stronger gravitational pull on the oceans

• Contributed to the mixing of the substances present in the primitive oceans

The evolution of Earth's oxygen atmosphere

• 4 billion years ago the earliest oxygen producing (photosynthesizing) organism occurred.

• With the presence of these organisms there was excess oxygen being formed.

• Eventually, oxygen built up in the atmosphere but this took millions of years.

What about the oxygen?• Microscopic Mojave Desert

– plants growing on the underside of translucent quartz pebbles

• endure both chilly and near-boiling temperatures

• scavenge nitrogen from the air, and utilize the equivalent of nighttime moonlight levels for photosynthesis.

– model for how plants first colonized land

– how they might have evolved on Mars

First oxygen producing organismsStromatolites

• Archaean era• 3.5 billion years old• Microscopic• Need only

– Nitrogen &– Carbon Dioxide

• Photosynthetic

(give off oxygen)

Archaean Era

Stromatolites(microscopic bacteria)on the rocks

Blue-green algaeCyanobacteria(Stromatolites)

Green sulfur bacteria

• Their environment must be oxygen-free

• need light to grow• They engage in

photosynthesis,

Black smokers

• hydrothermal vent found on the ocean floor

• Generally hundreds of meters wide

• formed when superheated water from below the Earth's crust comes through the ocean floor

• Rich in dissolved minerals from the crust, most notably sulfides,

Black smokers

• The temperature of the water they vent can reach 400 °C, but does not boil due to the high pressure it is under at that depth

• The water is also extremely acidic, often having a pH value as low as 2.8 — approximately that of vinegar.