Hello,

I already installed the marble software into my macbook pro, but it won't open. When I doble click the marble icon a popup window appears saying "Marble can't be opened because it is from an identified developer". Thanks in advance

Where did you install Marble from?
It sounds like your system is subject to some form of Apple store based restrictions, which are preventing Marble from launching - disabling these (which if it is possible will be done through System Preferences I suspect) should allow Marble to launch.