“Today, we know more about the moon than we do the ocean”. This quote by Jean-Michael Cousteau holds a truth: even though the ocean covers approximately 71% of planet Earth, we still know very little about it. Understanding what goes on beneath the sea is one of the utmost challenges of science.

Humans have always been attracted by the ocean, and the first ocean explorers were several coastal cultures in Greece and China, that around 5000 BC began diving into the sea to gather food and engage in commerce.

Modern Oceanography – the branch of science that deals with physical and biological properties and phenomena of the ocean – began only in the 18th century. Ferdinando Marsili, an Italian scientist and explorer, is considered the father of modern Oceanography. He is the first scholar to introduce scientific rigor into the study of the sea, and one of the first men in the world to carry out oceanographic research and to investigate the biology of the sea and the morphology of basins and coasts. He made field observations, studied the seabed in the Gulf of Lion, the classification of species, the currents and the properties of seawater, recalling that his entire scientific approach was based “on the experiments and observations he made himself on the spot”. In 1725, he published the “Histoire physique de la mer” about the discoveries of his oceanographic research of 1705-1706 in the Gulf of Lion, which is considered the first scientific treat on the ocean.

Another milestone in the history of modern oceanography is the Challenger Expedition (1872-1876), building on the recent discoveries of Charles Darwin aboard the Beagle, scientists aboard the HMS Challenger circumnavigated the world’s ocean with the main aim of gathering data on a wide range of features: ocean temperatures, seawater chemistry, currents, penetration of light in the deep sea, marine biodiversity, and the geology of the seafloor. The scientific results of the voyage, including the discovery of 4.700 species and the biological findings, were published in a report containing 50 volumes with more than 29,500 pages that took more than 20 years to compile, with the help of illustrators and artists. One of the most important discoveries of the Challenger Expedition was the localization of the Mariana Trench in the southwest Pacific Ocean. The technologies of the time measured a depth of almost 9,000 meters, something never recorded anywhere else on Earth. The Mariana Trench is confirmed to be the deepest known place on the ocean floor, with approximately 11.000 meters of depth.

In the early ‘900, close observation of the deep-sea environment and marine organisms was still unreachable: as of the late 1920s, the deepest that humans could safely descend in diving helmets was only several tens of meters. Submarines of the time had descended to a maximum of 115 meters but had no windows, so it was impossible for scientists to observe deep-sea environments. It was in 1930 that two Americans, a zoologist and an engineer, built a spherical steel vessel provided with portholes and suspended by a cable from a boat.  With the Bathysphere, the two were able to reach a depth of 900 meters in 1934, marking the first time that deep-sea animals were observed in their native environment by humans. The Bathysphere pioneered the manned exploration of the ocean.

In the last few decades, the exploration, study, and observation of the ocean have made great strides thanks to the collaboration among different disciplines and the advance of new technologies, such as satellites, echo-sounders and remotely operated vehicles. Further exploring the ocean in its depth and complexity is exactly what we need in a world of accelerating climate change, increasing population and economic demands. The cooperation of scientists, engineers, climatologists, geologists, and social scientists is enhancing the understanding of the ocean and its process, achieving a better representation of what lies beneath its surface.