Substances that heat up faster also cool down faster. explain why we observe greater fluctuations in air temperature over land than over water.

If we have greater fluctuations in temperature on land, that means that the air heats up and cools down faster. This means that water has less fluctuations because the temperature takes longer to heat up and cool down than it does for air. This basically means that water has a higher specific heat capacity than air. 

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The open ocean begins at the low-tide mark and extends to the end of the continental shelf

above statement is not a true statement about the open ocean because the open ocean has low levels of nutrients. most of the photosynthetic activity on earth occurs in the open ocean within the photic zone. organisms in the deep ocean are exposed to frigid temperatures and total darkness but it does not begin at the low-tide mark.