Interesting question! To be honest, the question about DNA is outside of my area of expertise. I better let a biologist handle that one. But I can make a suggestion about taking biology or earth science next year! If you are very interested in science, then I think you should take both! If it’s not possible to take both in one year, perhaps you could try to take one this year and one in another grade. I may be biased, but it seems to me that biology, chemistry, and physics dominate the high school science curriculum, and that earth science is the underrepresented physical science. I think that it is very important to learn about the earth that we live on and how we interact with its geologic, hydrologic, atmospheric, and biologic systems. Most people (in my experience) don’t know very much about what earth scientists do. Many are surprised to find out that earth scientists use all of the other physical sciences, including chemistry, physics, and biology in our studies. When I turn around and look at my bookshelf, I see texts on geochemistry, geophysics, and even “geomicrobiology”. In earth science, you can apply all of the other physical sciences to interesting questions about our earth, and even other planets!

Next generation antibiotics are actually HUGE in science right now, and will continue to be as bacteria develop resistance to current antibiotics (like MRSA has). I would definitely recommend biology, chemistry, and physics over earth sciences. Regarding aging, we aren't yet really sure how it works. You'll get a much better idea of how DNA and cells work in biology. Living forever is a lot harder than just keeping DNA replicating and accurate.