Question: During a battle between two extremely powerful space wizards, a beam of magical lightning has blasted a perfectly circular hole around 10 feet in diameter directly through an Earth-sized planet. In and out like a gunshot through paper. How would this impact life on the planet after this event, if at all?

NOTE: The incident occured about 150 miles south of the planet's north pole.

Answer: 
I would assume this depends on how the Beam did its work. If it just "deleted" the matter in its way, just about nothing would happen excpet that some random Animal will have a pretty bad day.

If the Beam melts its way across you may see a pretty big explosion on both sides of the Planet. The first when the Beam enters and the 2nd when it goes out. So overall, a bunch of Animals would have a bad day. But not much more.

If it pushes everything to the side, like a Force Field. Well then still not a lot would happen. Except someone in the distant future will see a strange long diamond bolt going from one side of the Planet to the other.
This is because at some point, or depth, the Beam pushes dense stuff into very dense stuff. Thus creating bling blings.

At the end of the day, 3 Meters just isnt that wide and the total amount of Energie blasted into the plant could be scrapt of as a Rounding Error.

For anything drastic to happen, you gonna need a wider beam. Making it more powerfull but keeping the diameter the same wouldnt do anything. Sure at some point the Impact spots would look like several nukes went down, but at some point it makes no difference anymore. You need to affect a bigger area at once.

Example, a Photon at Lightspeed dosnt hurt you. Even although it carries momentum. But let's say the Photon is 1 Meter across. Well then you are going to have a bad day.

The wider the beam is, the more stuff gets turned into dust and the bigger the Impact Explosion is.

Sorry for Misspellings , I am German.
Immediate Effect
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You're going to get a pair of volcanoes. They might turn out fairly small, but I think there is a good possibility of super-volcanic eruptions. Consider this: the pressure around the surface of the solid inner core[1] is estimated to be around 330GPa (3.3 million atmospheres).

A supervolcano[2] erupts when the gasses dissolved in the magma come out of solution and I think this is exactly what would happen when a 3m diameter cylinder of earth, going right through the core, simply ceases to exist. Maybe the magma will quickly plug such an "insignificant" hole but I wouldn't bet on it; I suspect it would be more like a water-main break, where the jet of magma would continue to erode the hole for a long time.

Long-term Effects
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A typical supervolcano erupts with such force that large amounts of material (thousands of cubic km!) are launched into the atmosphere and disperse, to some extent, across the majority of the planet. The widespread particulate clouds can lead to a decrease in global average temperature. However, in this case such effects are likely to be more limited due to the type of eruption. I think of it inflating a balloon and then releasing the air from it rather than popping it... only the release of magma could continue for a rather long time. Instead of fizzling out with the hole plugging up, we might instead see the hole widen with magma flowing out for a Very Long Time (see Siberian Traps[3]). In this case, it could be nearly life-ending!

Summary
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* Probably (super?)volcanoes!
* Effects could range from "ooh, another volcano" to "where have all the plants/animals/people gone?"

[1] <https://en.wikipedia.org/wiki/Earth%27s_inner_core>  

[2] <https://en.wikipedia.org/wiki/Supervolcano>  

[3] <https://en.wikipedia.org/wiki/Siberian_Traps>