OCEANS ACROSS SPACE AND TIME IS INSPIRED BY THE DIVERSITY OF OCEAN WORLDS THAT WE HAVE IN OUR OBSERVATIONAL GRASP AND JUST BEYOND OUR OBSERVATIONAL HORIZON. WHILE AT FIRST LOOK THESE EXTRATERRESTRIAL WORLDS MAY APPEAR ALIEN THE VAST AND DIVERSE PAST AND PRESENT OCEAN ENVIRONMENTS ON EARTH SHARE A STARTLING NUMBER OF SIMILARITIES WITH EXTRATERRESTRIAL OCEANS. BY DELVING INTO THESE MORE ACCESSIBLE OCEAN ECOSYSTEMS WE CAN LEARN MANY LESSONS ABOUT THE INTEGRATED HISTORY OF EARTH AND THE (POTENTIAL) ECOLOGY OF EXTRATERRESTRIAL OCEAN WORLDS. THUS TO MOTIVATE A COMPREHENSIVE UNDERSTANDING OF THE POTENTIAL FOR LIFE IN OCEANS ACROSS SPACE AND TIME WE WILL ADDRESS THE CENTRAL COMPELLING QUESTION: HOW DO OCEAN WORLDS AND THEIR BIOSPHERES CO-EVOLVE TO PRODUCE DETECTABLE SIGNALS OF A PAST OR PRESENT LIVING WORLD? SCIENTIFIC APPROACH: WE WILL ADDRESS THIS QUESTION BY CONSIDERING EARTH OCEAN ENVIRONMENTS THAT REPRESENT CONTEMPORARY REMNANT AND RELICT OCEAN ECOSYSTEMS ALL IN THE CONTEXT OF OBSERVATIONS AND MODELS OF EXTRATERRESTRIAL OCEANS. BY BRINGING TOGETHER A MULTI-DISCIPLINARY TEAM OF MICROBIOLOGISTS ECOLOGISTS OCEANOGRAPHERS GEOCHEMISTS LIMNOLOGISTS BIOGEOCHEMISTS SEDIMENTARY GEOLOGISTS PLANETARY SCIENTISTS GLACIOLOGISTS AND LIFE DETECTION SPECIALISTS WE WILL BE WELL POSITIONED TO ACHIEVE A STEP-CHANGE IN OUR UNDERSTANDING OF EXTRATERRESTRIAL OCEAN ECOSYSTEMS. OUR RESEARCH APPROACH HINGES ON INTEGRATING STUDIES OF LIFE AND THE ENVIRONMENT USING CUTTING-EDGE TECHNOLOGIES TO DISCOVER HOW THESE INTERACTIONS PROCEED AS THE ENVIRONMENT EVOLVES. SIGNIFICANCE: UNDERSTANDING PRESENT AND FORMER OCEAN WORLDS ALONGSIDE THE EARTH PROVIDES UNPRECEDENTED OPPORTUNITY TO UNDERSTAND PLANETS WITHIN AND BEYOND OUR SOLAR SYSTEM. IN SHORT THE NUMBER OF OCEANS THAT WE WILL DETECT IN OUR GALAXY STANDS TO INCREASE DRAMATICALLY IN THE COMING YEARS. HOWEVER OUR MODEL OF A HABITABLE PLANET AND WHAT THOSE BIOSIGNATURES ARE LIKELY TO BE IS INEXTRICABLY ENTWINED WITH OUR UNDERSTANDING OF OUR OWN OCEAN PLANET; DESPITE HUMANITY S LONG FASCINATION WITH THE OCEAN WE STILL DO NOT HAVE A CLEAR UNDERSTANDING OF ITS COMPLEX BIOSPHERE-ENVIRONMENT INTERACTIONS PARTICULARLY AT ITS EXTREME END STATES. THIS MEANS THAT NOT ONLY IS MUCH OF THE HISTORY OF THIS PLANET DIFFICULT TO OBSERVE OR INTERPRET BASED ON PRESENT EXAMPLES OR THE ROCK RECORD BUT THAT THIS FURTHER COMPLICATES OUR ABILITY TO UNDERSTAND THE OCEANS ON OTHER PLANETS. BY STUDYING THE QUESTION OF OCEAN WORLD EVOLUTION ACROSS SPACE AND TIME WE DIRECTLY ADDRESS GOALS 4 AND 5 OF THE ASTROBIOLOGY PROGRAM AS CONTAINED IN THE 2015 ASTROBIOLOGY SCIENCE STRATEGY. OCEANS ACROSS SPACE AND TIME WILL EXTEND AND EXPAND THE HISTORICAL SUCCESS OF NAI TEAMS WORKING IN ANALOG SYSTEMS TO UNDERSTAND THE HISTORY OF LIFE AND THE ENVIRONMENT.