I think that since humans evolved from the same ancestors as every other creature on the planet, we are part of it and, thus, nature. Just because we can communicate with each other and we have the power to dominate other species does not mean we are above nature. Our innovation is a part of us, therefore it is also a part of nature. Think about other creatures who use tools and make shelters. Are beaver dams unnatural? Are bird nests? Of course not. Our innovations and creations are just as much a part of nature as any other animal’s; the only difference is that ours dominate others in a harmful way.
Animal testing is unjust regardless of how you think about it. As stated above, we are not above them. What if another species ended up on top and they used us for experiments? Most people would agree that would be ethically wrong. Animal testing is not always effective, either. While many species have similar genetic compositions, none of them are exact, so we do not really know how a product will affect a human.
I think that the Earth has the capacity to heal itself, provided we do not destroy it first. This will also take an unfathomable amount of time. For example, the half-life of Plutonium, a by-product of nuclear fission used in power plants, is 27,000 years. There is no frame of reference that would allow someone who will live for probably around 80 years to wrap his or her head around 24,000 years. Do we really want to condemn our planet for thousands of years? Does it matter whether or not the Earth can heal itself after this point?