The phrase "oldest evidence" refers to the oldest known proof or clues that provide information or support for a particular theory, hypothesis, or idea. Full definition
He's using some 40 year old evidence (if it can be called that) to attempt to prove his point. (religion.blogs.cnn.com)
Older evidence suggests that classroom observations can be influenced by factors unrelated to performance, such as age and race. (carnegieknowledgenetwork.org)
«Oldest evidence of life on land found in 3.48 billion - year - old Australian rocks.» (sciencedaily.com)