2. Comparing the atmospheres of Venus, Earth, and Mars

3. The atmospheres of Venus, Earth, and Mars are different.
Let’s examine the differences.

4. Venus has a very thick atmosphere.
How did it form?

5. Very early in Venus’s history, it had liquid water on its surface.
After about one billion years, Venus began to become hotter.

6. As it became hotter, the atmosphere became filled with water vapor.
Water vapor is a greenhouse gas and traps heat in the atmosphere.

7. As Venus continued to heat up, hydrogen in its atmosphere escaped into space.
The oxygen in its atmosphere began to bond with carbon atoms, making carbon dioxide.

8. Venus did not experience geological events similar to those on Earth.
On Earth, rocks absorbed carbon dioxide.

9. Carbon in Earth’s atmosphere bonded with rocks, like limestone.
This removes a large amount of carbon in the atmosphere.

10. Venus did not experience geological events similar to those on Earth.
On Venus, carbon had nowhere to go, so it stayed in the atmosphere.

11. Carbon dioxide in the atmosphere increased.
As the carbon dioxide in the atmosphere increased, the temperature increased.

12. As more oxygen bonded with carbon atoms in the atmosphere, the pressure and temperature continued to increase.

13. The increased carbon dioxide trapped heat on Venus.
The led to a runaway greenhouse effect.

14. Temperatures increased until they became a constant 800o F.
Atmospheric pressures increased.

15. This is why Venus is the way it is.

16. At one time, Mars had a thicker atmosphere.
It also had a strong magnetic field, like Earth’s.

17. But, as the smaller planet cooled, Mars lost its magnetic field some time around 4.2 billion years ago.

18. The atmosphere was no longer protected.
Over time, the particles in the solar wind began to strip particles away from the Martian atmosphere.

19. Because Mars has weaker gravity, it could not keep particles in the atmosphere.
Eventually, most of its atmosphere was “blown off” into space.

20. Its current atmosphere is very thin.
It cannot retain heat from the Sun.
This is why temperatures can range from 65o F. during the day to –121o F. at night.

21. Earth has a thick atmosphere.
The atmosphere protects us from many of the harmful effects of the solar wind.

22. Why is Earth so different from Venus and Mars?
Early in the Earth’s history, Earth was hit by a Mars sized body.
This collision formed the Moon.

23. The formation of the Moon blew away much of the CO2 in the Earth’s atmosphere.
Excess CO2 was also absorbed during the formation of rocks (for example, limestone).

24. Less CO2 means less heat is trapped in the atmosphere which means a cooler planet.

25. This explains why the atmospheres of Venus, Earth, and Mars are different.

26. The presentation ends here.