The Marines are specialized at amphibious warfare. Basically they start the fight.
The Army is not specialized at any one thing but is structured for the long fight.
So in WWII for example, the Marines would land on the beach, fight to a certain point, then the Army would take over finishing off the enemy and rebuilding the island.
Also, the Army does everything the Marines do, but are just not specialized in those thing. For example in WWII, the Army actually did more and larger amphibious landings then the Marines did.
Marines hate to hear this, but they are kind of like an Army Airborne Unit. An Airborne unit is specialized at one thing, airborne attacks. Marines are specialized at amphibious warfare.
Other then the specialized areas, they do the same thing tactically as far as combat goes, take and hold land. The Army then goes a step further and has some capacity to rebuild after taking the land as well as long range operational logistics. Marines can only do tactical logistics internally. For example, the Marines can supply and transport a Marine Division or Marine Expeditionary Brigade, but the Army has the capability to supply and transport corps and do theater logistics for not only the Army and the Marines in theater, but Navy and Air Force ground assets as well.
Bottom line, Marines are intended for short term tactical responses, the Army is intended for long term strategic and operational purposes. So if you have a Non Combatant Evacuation, go with the Marines. If you are taking over a large piece of land, go Army.