The significance of Becquerel's discovery became apparent in 1903, when Pierre Curie and his young assistant, Albert Laborde, announced that radium salts constantly release heat. The most extraordinary aspect of this new discovery was that radium radiated heat without cooling down to the temperature of its surroundings. The radiation from radium revealed a previously unknown source of energy. William Wilson and George Darwin almost immediately proposed that radioactivity might be the source of the sun's radiated energy.
Detection of variations in the relative velocities of the primary and secondary seismic waves – expressed as Vp/Vs – as they passed through a certain zone was the basis for predicting the 1973 Blue Mountain Lake (NY) and 1974 Riverside (CA) quake.  Although these predictions were informal and even trivial, their apparent success was seen as confirmation of both dilatancy and the existence of a preparatory process, leading to what were subsequently called "wildly over-optimistic statements"  that successful earthquake prediction "appears to be on the verge of practical reality." 
First, System test plan is prepared to make our self ready to prepare the entire system which is being developed from the scratch. System test plan is prepared only if the application or product is completely new. And the application or product need to undergo all type of testing like Functional, Performance, Load, Certification, UAT etc.
Second, Integration test plan is prepared if a product or application being developed by several team or several developers and if one complete module output is going to be as a input for another module, then this Integration Test Plan will be useful to plan accordingly. So when two systems being integrated the possibilities of issues are like software compatibility, input variable map etc. So these needs to be tested completed when its integrated. Hope its clear now.