Specific heat capacity is the amount of heat required to raise the temperature of a substance by 1 K. It is expressed in the units J/ (kg*K).
A high specific heat of a substance means that a large amount of heat is required to raise the temperature of the substance.
Water is the substance with the second highest known specific heat capacity. at 4186 J/ (kg*K). To raise the temperature of 1 kg of water by 1 Kelvin requires 4.186 KJ of heat. This is mainly due to the presence of a large number of hydrogen bonds between molecules of water.
Water covers around 70% of the Earth's surface and its high specific heat plays a very important role as it is able to absorb a lot of heat without a significant rise in the temperature. When temperatures decrease, the heat which is stored is released, restraining a rapid drop in temperature. The combined effect of these processes is a buffering of temperature on the Earth.
A relatively constant temperature without spikes and drops is essential to sustain life, as most organisms require temperatures to remain within a narrow range for their survival.