How does the temperature of the earth vary as the depth increases from the surface to about 8 feet?

Answer 1

There are a lot variables that we need to know before we can answer your question.

What is the ambient air temperature?
What is the thermal conductivity of the earth at that location?
How much moisture is in the soil?
Are we dealing with dry gravel, swamp, or granite?
What is the specific heat retention of the earth at that location?
What is the geothermal flow (Q) at that location?
What is the altitude and latitude?

In general, the upper millimeter of the earth will be very close to the ambient air temperature, but it will lag a little behind the daily temperature changes (diurnal variation). The temperature of the upper few feet of the earth's crust - like your 8 foot scenario - will very closely approximate the average yearly temperature at that location. So on a hot summer day, the earth will be cooler, and and on a cold winter day, the earth will be warmer. The deeper you go, the less the variance will be from hourly/daily/monthly/yearly temperature changes of the atmosphere because the earth's specific heat retention is far greater than the atmosphere. The closer to the equator you are, the warmer the earth will be.

Now, if you are in an area of Precambrian Shield such as the Fennoscandian Shield in northern Finland, the heat flow will be very low, maybe 1.0 ucal/cm2/sec, and that means the temperature change with depth is small, and if you are in an area of high heat flow such as Yellowstone in Wyoming or Broadlands in New Zealand, the heat flow could exceed 2.0 ucal/cm2/sec.

The deeper you go in the earth's crust, the hotter it will get, but 8 feet won't be enough to measure it. By the way, the earth's heat is caused by radiogenic heat - the earth's core is a natural nuclear reactor!

Answer 2

according to normal lapse rate , the tempreature increases for every 6 meters to 1000meters of asent by this we can state that as one go deeper into the surface of the earth , the earth compraises of layers like mantel and core are present these are basically hot in nature we can state that the interior of the earth is hot weather it may be 8 or 9 feet height

Answer 3

8ft down, it is colder compared to the surface, because there is no sunlight. If you keep drilling down, it will get increasingly hotter because the Earth's core is a huge spinning ball of hot metal.

Answer 4

Drop by the geothermal consortium(?) web site. They have a lot of information about this type of info.