Earth science data are increasingly unlocked from their local ‘safes’ and shared online with the global science community as well as the average citizen. The European Union (EU)-funded project OneGeology-Europe (1G-E, www.onegeology-europe.eu) is a typical project that promotes works in that direction. The 1G-E web portal provides easy access to distributed geological data resources across participating EU member states. Similar projects can also be found in other countries or regions, such as the geoscience information network USGIN (www.usgin.org) in United States, the groundwater information network GIN-RIES (www.gw-info.net) in Canada and the earth science infrastructure AuScope (www.auscope.org.au) in Australia. While data are increasingly made available online, we currently face a shortage of tools and services that support information and knowledge discovery with such data. One reason is that earth science data are recorded in professional language and terms, and people without background knowledge cannot understand their meanings well. The Semantic Web provides a new context to help computers as well as users to better understand meanings of data and conduct applications. In this study we aim to chain up Semantic Web technologies (e.g., vocabularies/ontologies and reasoning), data visualization (e.g., an animation underpinned by an ontology) and online earth science data (e.g., available as Web Map Service) to develop functions for information and knowledge discovery. We carried out a case study with data of the 1G-E project. We set up an ontology of geological time scale using the encoding languages of SKOS (Simple Knowledge Organization System) and OWL (Web Ontology Language) from W3C (World Wide Web Consortium, www.w3.org). Then we developed a Flash animation of geological time scale by using the ActionScript language. The animation is underpinned by the ontology and the interrelationships between concepts of geological time scale are visualized in the animation. We linked the animation and the ontology to the online geological data of 1G-E project and developed interactive applications. The animation was used to show legends of rock age layers in geological maps dynamically. In turn, these legends were used as control panels to filter out and generalize geospatial features of certain rock ages on map layers. We tested the functions with maps of various EU member states. As a part of the initial results, legends for rock age layers of EU individual national maps were generated respectively, and the functions for filtering and generalization were examined with the map of United Kingdom. Though new challenges are rising in the tests, like those caused by synonyms (e.g., ‘Lower Cambrian’ and ‘Terreneuvian’), the initial results achieved the designed goals of information and knowledge discovery by using the ontology-underpinned animation. This study shows that (1) visualization lowers the barrier of ontologies, (2) integrating ontologies and visualization adds value to online earth science data services, and (3) exploratory visualization supports the procedure of data processing as well as the display of results.