How do you know that the marine environment is 1 billion years old?

Question: How do you know that the marine environment is 1 billion years old?

Asked by sumaya to Maria on 13 Jun 2010 in Categories: Your Research.
- Maria Pawlowska answered on 13 Jun 2010:
  
  Thanks for your question! It’s a good one I don’t get asked often enough. We know it’s 1 bln years old because we were able to date the lava deposits right beneath and above the rocks I work on through radiometric dating i.e. we measure radioactive decay of U-Pb (or how many uranium atoms fell apart and formed lead- we can do this because we know the rate at which it happens).

Question: How do you know that the marine environment is 1 billion years old?