Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: Researchers have discovered four extinct underwater volcanoes thousands of feet below the water off the coast of Sydney The calderas are believed to have formed 50 million years ago when supercontinent Gondwana was splitting up into the regions we now know as Australia and New Zealand. And this quartet of 'hotheads' may offer geologists clues about how exactly this tectonic movement took place. The volcanoes were discovered 125 miles (200km) off the southwestern Australian coast using the Investigator ocean explorer from the Commonwealth Scientific and Industrial Research Organisation (CSIRO). Scientists from the University of New South Wales Australia were searching for nursery grounds for larval lobsters when the sonar images spotted the volcanoes 16,100 feet (4,900 metres) underwater.Four volcanoes found in a cluster 125 miles (200km) off coast of SydneyResearchers found the ancient underwater formation by accidentCluster is 12 miles (20km) long, 4 miles (6km wide) and rises 230ft (700m)Experts believe they tell 'part of the story' of how Australia and New Zealand separated between 40 and 80 million years ago 
 Question:'The ship is constantly mapping the sea floor as it travels, opening up a previously undiscovered and unknown world,' explained _.

Commonwealth Scientific and Industrial Research Organisation