All the branches of life on Earth lead back to the very same trunk. That is to say that every terrestrial and aquatic organism is part of the same family tree. That’s not to say that LUCA, the last universal common ancestor was the first thing to ever live. On the contrary, life has sprung up many times on this world, as well as many others. However, everything that is alive today is definitely the genetic offspring of only one line of those primordial creatures.
This is actually fairly common among biological systems. For instance, about a hundred and fifty thousand years ago there were many different women alive but only the descendants of one lived all the way up through to the present moment. Only the children of the matrilineal most recent common ancestor, or MRCA, went on to have children of their own throughout the ages. In a similar manner before that, every kind of organism other than the last universal common ancestor went extinct at some point along the way.
This means all the genes that are the same in every life-form were inherited from LUCA. Then, mutations and adaptations made all the life on Earth what it is today. Every trait evolved from the minimal genome of the last universal common ancestor. They only had about a thousand genes, while modern humans have about twenty times that amount. As such, four billion years ago LUCA was incredibly simple compared to the current complexity of creatures like us. They were quite different from us because they only contained RNA while we have DNA. Thus, the last universal common ancestors were some kind of proto-prokaryotes, while we are highly advanced eukaryotes.
Although we may not know exactly what LUCA was, we know that it must have lived. Plus, as time goes on microbiologists will undoubtedly uncover more and more of our shared heritage. The thing to note is simply the fact that all life is related. Ultimately, every tree of life has an endless amount of branches but only one trunk. Thus, every native form of life on any given planet is interconnected both environmentally and genetically with every other, tracing all the way back to the last universal common ancestors themselves. Plus, when you get right down to it, there’s nothing more important than knowing where you came from, with the exception of where you’re going maybe. Either way, now you know.