For a basic 500 square feet project in zip code 47474, the benchmark cost to Insulate Your Home ranges between $0.63 - $1.43 per square foot* . To estimate costs for your project: 1.
So in answer to your question, the oldest fossils are stromatolites, and the life forms that created those fossils were prokaryotic bacteria and algae like cyanobacteria.
Indeed, some scientists think life appeared the moment our planet's environment was stable enough to support it. The earliest evidence for life on Earth comes from fossilized mats of cyanobacteria called stromatolites in Australia that are about 3.4 billion years old.