Unsure about this usage of か


I recently encountered this sentence:

> 床には血痕が残っている。 **かなり時間が経つのか** 血が固まっている。

I believe I understand that the second part is saying the blood is dry (or has
hardened) because quite some time has passed. I'm not sure what the か after
経つの is doing -- is the speaker not quite sure if that's the right explanation
(something like, "The blood has hardened, perhaps because a lot of time has
passed")?




Your explanation is right.

The speaker is not quite sure if that's the right explanation (something like,
"The blood has hardened, perhaps because a lot of time has passed").

The grammar you are looking for is defined in [this
page](http://dictionary.goo.ne.jp/jn/34861/meaning/m0u/%E3%81%8B/), which
says:

> 疑いの気持ちで推定する意を表す




Your explanation is right.

The speaker is not quite sure if that's the right explanation (something like,
"The blood has hardened, perhaps because a lot of time has passed").

The grammar you are looking for is defined in [this
page](http://dictionary.goo.ne.jp/jn/34861/meaning/m0u/%E3%81%8B/), which
says:

> 疑いの気持ちで推定する意を表す

