The proton-proton chain reaction is a carriage load of horse doo-doo.
They used a philosophically invalid model (protoplanetary disk) to explain the formation of the Earth and Sun.
Radiometrically dated the Earth (older than 3.5 billion years)
Went back on the protoplanetary disk model (philosophically invalid because it violates conservation of angular momentum rules), thus solidifying the assumption that Earth and the Sun are roughly the same age.
Made the Sun needing to be older if not as old as the Earth, therefore meaning it had to be shining the entire time as it does currently.
Find a type of hot event which takes a long time to occur, deuterium producing events. (They are rare enough for the pseudoscientist Eddington, which is really strange because diprotons immediately decay back into two protons.)
Cover their asses with the statement: If the deuterium producing events were faster, the Sun would have used up its hydrogen fuel in its core. (This is a load of crap because diprotons immediately decay back into two protons, this should have never been accepted! This leaves room for them to try and make up for lost ground if the Sun turns out to be much younger, they just will re-invent the deuterium forming process.)
Ignore the fact that nobody has taken internal temperature measurements of the Sun. (Holy shit! You got to be kidding me! No temperature beneath the surface of the Sun has been found to be hotter than the requirements to overcome the coulomb barrier!)
Ridicule everybody who points this stuff out and claim omniscience!!!