You don't have to understand everything to understand anything. Scientific theories are always abstractions that reduce the complex interconnected universe to a workable surface area we are trying to explore in order to produce a model that can be used to make predictions about the larger world that in turn can be tested, refined, or shit canned as appropriate.

You can say we can't possibly understand how the heart works because we do not understand the entire evolutionary tree leading up to the human race and how the circulatory system evolved over billions of years and ergo heart transplants are impossible. This is trivially false and its false for the same reason parent posters assertion is false. Everything is how it is because of initial conditions ergo everything connects back to time zero but we can still use the abstract understanding we do have to make models and predictions.

> Life connects back to time zero because everything prior was an important boundary condition, e.g. heavy metals made through exploding stars supporting elemental composition of life, etc.

The initial conditions were so uniform that it doesn't take the same level of detail to understand what happened, and we can look all the way back to the CMBR. A particle-by-particle reconstruction of interactions since the big bang won't make much of a difference in our understanding of what happened on Earth. Virtually all of the interactions arrived in our solar system in a very noisy fashion during star formation and it was up to the resulting sun to pump negentropy into the rocks and other matter.