Atmospheric History of Venus The Unique Atmosphere of Earth

Very thick atmosphere: 90 bar (Equivalent to 0.6 mi under water) Composition: Carbon Dioxide 96.5% Nitrogen 3.5% (everything else is in the ppm range) Average temperature: 870° F = 465° C Everywhere, all the time At high altitudes, temps are ~ 65° C Sulfuric acid clouds and rain: It evaporates before reaching the ground High altitude winds circle planet in 4 days: > 200 mph!

While Earth has very little of either in its atmosphere? Being about the same size as Earth, and forming near it in the solar nebula, Venus should have been made of the same stuff Outgassing should have produced enormous amounts of carbon dioxide and water vapor on both planets Most common volcanic gases: Water vapor Carbon dioxide Nitrogen Why would Venus end up with LOTS of carbon dioxide in its atmosphere and almost no water… While Earth has very little of either in its atmosphere? Earth’s atmosphere: Nitrogen 78% Oxygen 21% Argon 0.9% Carbon Dioxide 0.04%

Earth still has lots of both carbon dioxide and water: (in the rock) The liquid water provides a mechanism for locking away the carbon dioxide Water

Venus is too hot for liquid water (So the carbon dioxide is not dissolved and incorporated into rock) Water vapor in the atmosphere is broken apart by UV from the Sun (no stratosphere) The hydrogen is lost to space (Thermal escape) The oxygen is either lost to space or is removed through chemical reactions (Isotopic ratios of 1H versus 2H support this model)

What would happen if we could move Earth to Venus’s orbit? To understand the different atmospheric histories of Earth and Venus, consider this: What would happen if we could move Earth to Venus’s orbit?

What is the most abundant gas in Venus’s atmosphere? A) Oxygen B) Nitrogen C) Water vapor D) Carbon dioxide E) Argon

What is the most abundant gas in Earth’s atmosphere? A) Oxygen B) Nitrogen C) Water vapor D) Carbon dioxide E) Argon

What is the second most abundant gas in Earth’s atmosphere? A) Oxygen B) Nitrogen C) Water vapor D) Carbon dioxide E) Argon

If we could magically move Venus to Earth’s orbit, would it become like Earth? A) Yes B) Probably C) Maybe D) No

The Atmospheric History of Earth If Earth started out so similar to Venus and Mars, how did it end up so different?

Where did the oxygen and ozone come from? LIFE

What has kept the CO2 in our atmosphere at a reasonable level? The CO2 cycle 60x 170,000x

The CO2 cycle is Earth’s thermostat

While Earth has gone through ice ages and even “snowball” phases, the CO2 thermostat has pulled Earth out of those cold times

What happens to the CO2 cycle if average global temperatures rise slightly? A) Warmer temperatures lead to less water vapor in the air, allowing atmospheric CO2 to build up. B) Warmer temperatures lead to less water vapor in the air, lowering the amount of atmospheric CO2. C) Warmer temperatures lead to more water vapor in the air, lowering the amount of atmospheric CO2. D) Warmer temperatures lead to more water vapor in the air, allowing atmospheric CO2 to build up.

And now we’re interfering with that thermostat We’re releasing CO2 at a rate over 200 times faster than volcanoes The rise in CO2 is undeniable We know that human activity is driving it because the atmosphere is becoming enriched with molecules of CO2 carrying the distinct isotopic ratio present in fossil fuels.

Average global temperatures are also rising

Average global temperatures are also rising Only models that include human release of greenhouse gases match the observed temperature increase This modeling, along with isotopic ratios in atmospheric CO2, tells us clearly that current global temperature increases ARE a result of human activity

Where is most of Earth’s carbon dioxide? A) In the atmosphere B) In the oceans C) In the rainforests D) In rocks