This paper focuses on the problem of information systems evolution. Ideally, changes in the requirements of information systems should be defined and managed at the conceptual schema level, with an automatic propagation down to the logical database schema(s) and application programs. As one step more towards the achievement of this ideal approach, we propose here a framework for the evolution of temporal conceptual schemas of information systems. Our framework uses a reflective architecture with two levels: meta schema and schema, and two loosely coupled information processors, one for each level. We define a temporal minimal meta schema, and we show, using some examples, how to extend this minimal meta schema to support any usual conceptual modeling construct. We also show how the framework can be used to specify different kinds of schema changes. These changes are defined as meta external events, with explicit and implicit effects over the meta information base/conceptual schema and the information base. Two detailed examples are given to illustrate this approach.