Certain "Adventure" cards have a prerequisite icon that's a picture of a book with a nuclear symbol on it. There's only one card that involves science "Career: Rocket Scientist", and there's already a symbol for "degree", so I'm not sure what it's supposed to mean and what is required before playing it.
It's a Passport.
The symbol (shown here) is actually supposed to represent airplane travel around the world.
The Rules sheet (PDF) doesn't define this symbol explicitly, but does indicate the existence of a Passport symbol requirement:
You can only have ONE Passport and ONE Wedding card in your life story at any one time. If you 'Lose Your Passport,' you can replace it with another one later in the game.
Board Game Geek user Samuel Wolf posted this list of cards, which includes the symbol that is needed for each card. Of all the symbols, all but this one are either specified in the rules (e.g. Wedding, Degree) or are self-explanatory (e.g. need an Airplane to "Learn to Loop-the-Loop"). The only symbol left is the one you refer to, so it must be the Passport.