I’m currently aboard the R/V Atlantis, just northwest of Rapa Nui (Easter Island) with 15 scientists and 2 very cool robots. We’re exploring the Pito Deep, a point on the ocean floor where two tectonic plates have rotated a section of oceanic crust and caused the lowermost portion of it to be exposed. This means that we can observe and sample rocks which are usually buried kilometres deep, we only need to pick them up off the seafloor.
That still doesn’t make it easy as there is nearly 6 kilometres of water between the seafloor and our ship. That’s where the robots come in. Sentry and Jason work as a team to map out and explore the bottom of the ocean. Sentry is an autonomous underwater vehicle that maps bathymetry, records magnetic fields, and measures water properties along a pre-programmed path. Jason is tethered to the ship and remotely operated by an onboard pilot; it has many high-resolution cameras and two robotic arms for picking up samples.
So why go to so much trouble to get these rocks? Well first of all they help us understand how the seafloor is formed. We have more rock samples from the moon than from fast-spreading oceanic ridges like this one and this expedition is a step towards correcting that.
Second, the seafloor holds a record of Earth’s magnetic field. Every time a new bit of ocean crust cools, the magnetic minerals align themselves just like a compass, forming a series stripes throughout the ocean. These have been well mapped for over 50 years now, leading to the acceptance of plate tectonic and continental drift theories. However, this has only ever been done in two dimensions. The unique geometry of the plates at this site allow us to see how these magnetic boundaries behave in a third dimension (depth), which has never been mapped before.
Third, 23 years ago another expedition documented the presence of a “black smoker” hydrothermal vent at this site. This is where fluids that have seeped into the crust and been heated erupt in geyser-like jets. We’re interested in finding and exploring these because they play a critical role in global seawater chemistry and support unique ecosystems that cannot be found anywhere else. These are some of the few ecosystems on Earth that are not ultimately based on photosynthesis but instead on chemosynthesis. Many believe that hydrothermal vents are a promising candidate for the environment in which life on Earth first originated.