as it is well known 和 as is well known的句子结构区别?

缺乏上下文,不好断定.
as it is well known,应当是引导原因状语从句,且正常语序：因为/由于众所周知的.
as is well known,as 是关系代词,指代后面的一个句子或事实.
e.g.As is well known,the Earth goes around the Sun.
= The Earth goes around the Sun,as/ which is well known.