A cold front is the transition zone where a cold air mass is replacing a warmer one, (They move more slowly than warm front's.) Others are Characteristics of cold front's and they move faster than warm.
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i hope this helps you
from google:
"The Earth gets hotter as one travels towards the core, known as the geothermal gradient. Geothermal gradient is the amount the Earth's temperature increases with depth, indicating heat flowing from the Earth's warm interior to its surface. On average, the temperature increases by about 25°C for every kilometer of depth"
