O2 not only supports life, it also protect life!
UV light can break the water molecules to release oxygen, but the contribution is small….
The Role of the Magnetic Field of Earth
Another important characteristics of the Earth is its magnetic fields, which shield us from the bombardment of the high-energy charged particles, mostly from the Sun.
Without magnetic field, the high energy particles of solar wind can strip much of the Earth's atmosphere by breaking the bounds between the atoms in the air molecules
N2 → N + N
O2 → O + O
H2O → H + H + O
The lighter gases then have higher probability of acquiring velocity higher than escape velocity and escape from Earth!
Water On Earth in the Past
Was it always like this on Earth
Yes. Water was plentiful throughout most of Earth's history, for about three billion years.
No! Geological evidences suggest that Earth used to be covered by ice about 600-700 million years ago
Snowball Phase.
How did Earth recover from the snowball phase
Once the water was frozen, CO2 can no longer be removed from the atmosphere by dissolving in water interruption of the CO2 cycle.
Increased CO2 level in the atmosphere leads to stronger greenhouse effect, which warms the atmosphere.
Higher temperature melt the ice restoration of the CO2 cycle.
Comparative Planetology
Mars and Venus are very similar to Earth in their size and location to the solar system. However, their surface environments are drastically different from that of the Earth today. By understanding how Mars and Venus end up with their current state, we may be able to better understand our Earth…
Mars
Mars image from Hubble Space Telescope
Martian Season
The tilt of Mar's rotation axis with respect to its ecliptic plane is 25.19°
The eccentricity of Mar's orbit around the Sun is 0.093
The seasons on Mars are affected by both its orbital distance and its axis tilt.

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