Water and land heat unequally due to the fact that they produce different heating capacities. Heat capacity is defined as the amount of heat, measured in calories, required to change the temperature of a substance by one degree Celsius. Water has a higher heating capacity than land.
The sun provides a steady flow of energy in the form of heat to the outer atmosphere. This energy is called the solar constant. This energy is transmitted through the outer atmosphere into Earth's atmosphere, where it is scattered, reflected or absorbed. Solar warming is most intense near the equator and the least intense at the North and South Poles.
As land and water absorb this energy, land masses heat at a much faster pace than water bodies. As a result, land is hotter during the day and cooler during the night than water bodies such as oceans.
Due to the fact that oceans are able to store and release large amounts of heat slowly, they are largely responsible for Earth's temperature moderation. This is why coastal areas have fairly constant temperatures throughout the year. Inland areas experience greatly varying temperatures through the seasons due to the rapid heating and cooling of surrounding land masses.