[ncmncm]

If only all problems were as trivially ignorable as this one.

The radius of the Earth is 4000 miles. A 10-mile hole is thus 1/400 of the way to the center. You may as well worry that scratching the skin of an apple might damage the seeds.

[dotancohen]

Actually scratching the skin of an apple does negatively affect the apple - the part of the "mantle" under the scratch begins to rot right away.

Look at a graph of the temperature of the Earth as a function of depth. The temperature jumps tremendously below the crust, and is much more stable per depth below. The crust is the insulation of the Earth - and damaging that crust might affect the mantle is ways we cannot yet imagine.

The answer remains "we don't know".

[ncmncm]

Hint: the mantle is not made out of apple flesh, it starts much, much deeper than 10 miles most places, and nothing exists that can eat it.

[dotancohen]

It could also leak out, loose heat, and drilling down to it could trigger earthquakes and eruptions.

The argument "it's big, we can't affect it" has been proven wrong in the case of the atmosphere, and again in the case of the ocean. It is no longer a sound argument.

[ncmncm]

"It's big, we can't drill more than a negligible fraction of the way to it" remains as true as ever. So, no, we cannot make it leak out, lose heat, or trigger earthquakes or eruptions. It will still be almost as hot in a half-billion years when the sun engulfs and vaporizes it, whatever we do.

Eruptions in Siberia, and later in India, not long ago geologically, released more heat in a (geologically) short time than we could use up in a million years, with no effect on the Earth's magnetic field.

[spurgu]

Just because we haven't discovered giant planet-eating space aliens yet doesn't mean they don't exist.