Both the rotational and vibrational modes are quantized, requiring a minimum temperature to be activated. The " rotational temperature " to activate the rotational degrees of freedom is less than 100 K for many gases. For N 2 and O 2, it is less than 3 K. The " vibrational temperature " necessary for substantial vibration is between 10 K and 10 K, 3521 K for N 2 and 2156 K for O 2. Typical atmospheric temperatures are not high enough to activate vibration in N 2 and O 2, which comprise most of the atmosphere. (See the next figure.) However, the much less abundant greenhouse gases keep the troposphere warm by absorbing infrared from the Earth's surface, which excites their vibrational modes. Much of this energy is reradiated back to the surface in the infrared through the " greenhouse effect."