hello, my brother is an archaeologist
Oh, that's really cool. I'm into that, too. I got into it because it's a study of human prehistory and history, all the way back to the first stone tools in East Africa 3.3 mill years ago, until now. 
its amazing how far we go back but have limited written records of our existence
It really is! And archaeology is specifically important when trying to learn about prehistoric societies, where, just like you said, there are no written records to look at.
i guess that is where archaeology comes in, trying to figure out our prehistory
Yeah, there's so much to figure out within it, since it covers 99% of the human past. We're talking from the Paleolithic all the way until the advent of literacy in all the societies across the globe.
when you look at human history, the advancements we made in a short time is amazing
It really is. That's what's great about archaeology, is one of its main goals is to understand culture history and to reconstruct the past to understand how changes in human societies happened over time.
but eventually we will become extinct and maybe alien archaeologist can dig us up and study us :)
Hah, that's a good point. They'll dig us up and look at our artifacts, our architecture, and things like biofacts and ecofacts--even our cultural landscapes too!