Consciousness is a topic I have interest in. At it’s most basic level, it’s just awareness, but in looking at all the different ways it manifests, I see it mostly as an emergent property that arises from various degrees of awareness. As such, I don’t think it makes sense to say a person is conscious, a tree isn’t, so there must be some hard line where a lifeform on one side is conscious and one on the other side is not. It’s not all the different from asking a question like “who was the first human?” We can say we’re human, and we can say that our ancestors at a point in the past are not, but we can’t just say some person was the first human and his parents were not.
Similarly, we can all agree that humans are conscious, but we also clearly see being asleep as unconscious. One of the aspects of sleep I find most fascinating is that, like as above, there doesn’t seem to be a clear line of awake and asleep. In general, one slowly loses awareness, but perhaps if something interesting comes up during that process, I seem to have an awareness that I was in that process when I received that stimulus, and then suddenly remember things that I probably wouldn’t have if that process had continued.
And our growth and maturation are not unlike that, except in reverse. We all have pretty solid ability to make decisions and remember things clearly at a certain age, and it gets progressively hazier younger and younger. We all may have earliest memories, but chances are they’re less distinct than later memories, our brains’ connections and ability to manifest consciousness gets more and more complex as we age.
So, in this regard, I think it’s quite fair to say that pretty much any form of life with brains, and possibly even some without them, could be described as conscious, it’s just a matter of what that degree of consciousness is. I think few would dispute that a chimp is conscious, but to a less degree than humans, dogs less so, etc. But even still, there’s different ways of being aware, so I don’t even think we can reasonably look at it as a continuum. For instance, there’s awareness of one’s surroundings, there’s self-awareness, there’s an ability to interact with one’s surroundings and communicate, etc.
Ultimately, though, unfortunately these are rather vague questions being posed by the OP, and consciousness is such a broad topic with varied opinions and different types of research, that all you’re really going to get are fairly vague responses.