I read this background article the other day: In coastal regions, sea breezes and land breezes can be important factors in a location's prevailing winds. The sea is warmed by the sun more slowly because of water's greater specific heat compared to land. As the temperature of the surface of the land rises, the land heats the air above it by conduction. The warm air is less dense than the surrounding environment and so it rises. This causes a pressure gradient of about 2 millibars from the ocean to the land. The cooler air above the sea, now with higher sea level pressure, flows inland into the lower pressure, creating a cooler breeze near the coast. When large-scale winds are calm, the strength of the sea breeze is directly proportional to the temperature difference between the land mass and the sea. If an offshore wind of 8 knots (15 km/h) exists, the sea breeze is not likely to develop.  I am facing a new situation today: Jackie and Mark are two friends who are spending a day at the beach. Jackie wants to go out on the boat to spend some time on the ocean, but Mark wants to lay out on the beach and relax. Since they can't agree, Jackie goes out on the boat alone while Mark stays behind on the beach.  Using the knowledge I acquired from the background article, how should I answer correctly the following question regarding my new situation: Is the air around Mark more or less dense than the air around Jackie?

less