it is known to all that 和as is known to all that 区别

都表示“众所周知”,但是用法不同
It is known to all that the earth is round.it是形式主语；that引导主语从句,是真正都主语
As is known to all,the earth is round.中间有逗号,as 引导从句,the earth is round是主句