There is a DNA sequence that is found present in all living organisms; you and the tiniest of bacteria share this sequence as a part of your genetic makeup. Scientists say this makes it the oldest bit of DNA in existence.
“Arguably, the most remarkable DNA sequence on Earth is GTG CCA GCA GCC GCG GTA ATT CCA GCT CCA ATA GCG TAT ATT AAA GTT GCT GCA GTT AAA AAG. It is present in every single living organism – even in organisms not technically classed as alive such as giant mimiviruses. The reason the sequence is so widespread is that it existed in the common ancestor of all life. Carrying out a crucial process, it has remained unchanged for 3 billion years: the oldest fossil in your body.”
‘What a Wonderful World’ by Marcus Chown, pg. 48