Why double in C is 8 bytes aligned?

Question

I was reading a article about data types alignment in memory(here) and I am unable to understand one point i.e.

Note that a double variable will be al

Answer 1

Aligning a value on a lower boundary than its size makes it prone to be split across two cachelines. Splitting the value in two cachlines means extra work when evicting the cachelines to the backing store (two cachelines will be evicted; instead of one), which is a useless load of memory buses.