How does classification help us understand present and past life on earth?

By having a scientifically recognized classification system, scientists and also even general enthusiasts such as yourself have a widely respected and continually researched area to find reliable information about almost every known species. This system includes not only extant (living today) species but also extinct species of plants, animals, and even unicellular organisms. This system allows us to see the relationships between each individual species and what possible characteristics that they might share or possibly not share at all. It also gives a a very reasonable and possible glimpse or idea about how evolution has transformed and affected every single species on this planet and how we got to where we are today. Such as in the beginning there were unicellular organisms but now all you have to do is simply look in the mirror to the see just how far we've come from that simple beginning. If you're really interested, this is a really good website and somewhat easy to navigate.

http://tolweb.org/tree/