Could a gamma ray burst destroy life on Earth?

[Rynn]

I wanted to know just how damaging a gamma ray burst would be to a planet like the Earth. I browsed through a paper [link 2] by Brian Thomas, who implys that the consequences of a GRB would be fairly minor. His study was very detailed, but based on a strange assumption. Namely, that during this cataclysmic event, the Earth would be subjected to an energy influx of (only) 100 kilojoules per square meter.

Looking through the paper it is annoying that the authors don't explain that assumption, there are plenty of citations however so have you checked those?

-With this information, I decided to do some calculations of my own. I know that a distance of 1 light year is equal to 9.46E12 kilometers. I also know that a typical GRB releases an energy equal to roughly 1E44 joules.
-I then found out that a circle 1 light year in diameter has an area of 7.03E25 kilometers. And that a circle 136 light years in diameter has an area of 1.3E30 kilometers.
-Therefore, an area of 1 square kilometer will receive an energy of 7.69E13 joules. Thats 76 terajoules! 
-And since there are 1 million square meters in a square kilometer, each square meter will receive an energy of 7.69E7 joules. Thats 76 megajoules.


So, what conclusions can we take away from my calculations? Simple. If the Earth were to suffer the monumental misfortune of being hit by a gamma ray burst, then it truly would be a catastrophe. The consequences would be far more serious than what was predicted by Brian Thomas. His paper assumed an energy influx of only 100 kilojoules per square meter. In the scenario posited in link 3, however, the Earth would be subjected to an energy influx of 76 megajoules per square meter.

Your maths is right but it is unclear from the paper if the authors were referring to total energy or the energy that reaches the ground (as most of the energy is absorbed by the atmosphere). The easiest thing to do to check is to just email the authors and ask for clarification on the assumption. It's quite common in academia to do this, so long as you are polite about it and do not take up too much of their time.