1. Atmospheric History of Venus
The Unique Atmosphere of Earth

2. Very thick atmosphere: 90 bar (Equivalent to 0.6 mi under water)
Composition:
Carbon Dioxide %
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!

3. 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%

4. 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

5. 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)

6. 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?

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

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

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

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

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

12. Where did the oxygen and ozone come from?
LIFE

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

14. The CO2 cycle is Earth’s thermostat

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

16. 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.

17. 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.

18. Average global temperatures are also rising

19. 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

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