Mercury is a set of tools for harvesting, searching, and retrieving metadata and data. Mercury harvests metadata and key data from contributing project servers distributed around the world and builds a centralized virtual index. The Mercury search interface provides a single portal to very quickly search for data and information contained in disparate data management systems, each of which may use different metadata formats. The search interface then allows users to perform a variety of fielded, spatial, and temporal searches across these metadata sources. Version 4.0 of the Mercury toolset provides orders of magnitude improvements in search speed, support for additional metadata formats, integration with OpenLayers and Google maps API for improved spatial queries including polygon search and Sematic searching using Ontology-based framework. Other features include, facetted type search, support for RSS delivery of search results, and enhanced UI. This centralized repository of metadata with distributed data sources provides extremely fast search results to the user, while allowing data providers to advertise and distribute their data and maintain complete control and ownership of that data. Mercury is developed and managed at Oak Ridge National Laboratory and is currently being funded by three federal agencies, including NASA, USGS and DOE. It provides access to more than 300,000 Bio-geo-chemical and ecological data; 30,000 scientists use it each month.