would have done 用法1 Such a quantity of material would have blocked~the sunlight completely from reaching the surface,plunging Earth into a period of cold and darkness that lasted at least several months.2The explosion is also calculated to have produced vast quantities of nitric acid and melted rock that sprayed out over much of Earth,starting widespread fires that must have consumed most terrestrial forests and grassland.would have done 我只知道是虚拟语气 表示“

would have done 用法
1 Such a quantity of material would have blocked~the sunlight completely from reaching the surface,plunging Earth into a period of cold and darkness that lasted at least several months.
2The explosion is also calculated to have produced vast quantities of nitric acid and melted rock that sprayed out over much of Earth,starting widespread fires that must have consumed most terrestrial forests and grassland.
would have done 我只知道是虚拟语气 表示“本来会发生” 也就是“实际上没有发生”
但是请看文中第一句话里边 would have blocked
这两句话都是在讲历史上一次陨石撞击地球的事件 这些事情都是实际发生的事情
根据上下文 这里不应该表示“本来会发生”
那么请问这个would have done 是不是虚拟