I break under pressure, but don't worry. I can take the heat.
I am ancient. Time is important to me, it kept me from going soft.
I share some qualities with desserts, but when I am eaten, I kill.
I am a window to the past, and through trial by fire, I help make the future.
Think about donuts and sugar cookies, and the process by which they are made.
Now that it has been answered, a couple notes about it:
Line 1 refers to the fact that clay (and all ceramics) can be heated to incredible temperatures without breaking. Line 2 is pretty self-explanatory, but I think that line 3 is the hardest. It refers to the fact that clay is 'baked' in a kiln, but also to the 'glaze' that often covers ceramics. It perhaps is a little known fact, but clay with a fine consistency is actually very dangerous to ingest. Finally, line 4 refers to ancient pottery showing archaeologists the past, but clay still has many uses in building and pottery today.
My first puzzle! Please let me know if I can improve this post in any way. Thanks.