This paper presents OpenEarth-Agent, the first tool-creation agent framework designed for open-environment Earth Observation. Unlike traditional tool-calling agents confined to closed environments with pre-defined tools, OpenEarth-Agent employs adaptive workflow planning and dynamic tool creation to generalize across diverse multi-source satellite data and heterogeneous remote sensing tasks. The framework integrates multi-stage tools with cross-domain knowledge bases, enabling robust execution throughout the entire Earth Observation pipeline. This approach represents a significant advancement in autonomous EO systems by moving beyond narrow, predefined toolkits to an open-ended, adaptive framework capable of handling unseen data modalities and novel tasks in land surface monitoring applications.