1.On Planet Earth there have been forms of life and living creatures for a thousand million years before the advent of human beings. According to modern science.
2. How do we interpret the reincarnation scheme of the six lokas during this first thousand million years? Or the first three thousand million years? Especially concerning the beings that are born as the present humanity.
3. Is there a basis for this view in the Abhidharma and Sutra pitakas? They nevertheless say that reincarnation is beginningless, and therefore we have existed during the mentioned geological eras.
4. If you want to counteract the teaching of Batchelor et al you must have a coherent teaching of reincarnation, a teaching that explains the geological eras in a logical and believable way.
If we only define "human realm" as meaning mammal/primate/homo sapiens, then yes, of course. You are right. There can be no human realm on Earth before a certain time, before certain conditions arise (it's always about conditions arising). But "human" is only a term that we homo sapiens have invented. When we talk about the "human" realm in Buddhist terms, we are referring to a state of mind which is experiences temporary happiness and sadness, is never fully content, which changes a lot, and so on. It also is a state of mind which can also grasp the teachings of the Dharma.
So, Buddhism is not talking specifically about hairy bipeds. In fact, no two humans are exactly the same. From that aspect, you could even argue that there is really no such thing as a human realm, or of humanity, or the human race. It depends on how you categorize things. We are also a member of the ape family. So, we are also a little bit animal. We can also experience the various traits of the other realms. But usually we do not see hungry ghosts or devas (although we meet people who exhibit some of those qualities), because the conditions are not there for that to happen. We experience humans and animals, because the conditions are there...carbon, water, a suitable planetary environment for now.
This does not mean that the six realms only describe psychological states in literal terms, as is sometimes suggested. When someone asks if the other realms are 'real' or are we just talking about mental states, feeling greedy or horny or proud or jealous whatever, 'real' becomes a problematic term. The other 5 realms are no more 'real' than this one. So, depending on how 'real' your experience if this realm is, you can guess how 'real' a mind experiencing another realm is.
When the dharma texts refer to 'beings wandering in the realms of samsara since beginningless time' or whatever, that is because the mind, or more accurately, the causes of cognition, of awareness, do not depend on one set of physical properties or another, or any duration of time. But when the conditions are right, mind manifests as apparently tangible reality, just as the one we are experiencing right now.