I happen to think that 135 years is ridiculous when we're talking about geological time frames.
the only one talking about geological time frames is you. the rest of us understand that 135 years is more than enough to determine a trend in a climate signal.
55 million years ago the earth was a different place, with a different continental layout (hence no glaciation of the antarctic and greenland). the natural cycle worked completely differently. it's meaningless to bring that up to try to compare to the current epoch.
likewise, it's meaningless as to determining the cause of current warming. the greenhouse effect is basic science. we can measure the stuff we're dumping into the atmosphere. we can determine how much of it is us. we can calculate the effect.
we can use the PETM as a proxy as to how the earth and the biosphere will react to sharply rising CO2 levels but it doesn't inform us much at all about what is causing current warming unless you happen to find similar phenomena to back then. which we haven't found and you cannot present.