The scientists from the International Ocean Discovery Program (IODP) on board the Joides Resolution for Expedition 360 planned to drill a deep hole into the Earth's crust below the Indian Ocean, that they hope in the future will ultimately penetrate the Moho.
The team led by Professor Chris MacLeod, was looking for evidence that might overturn currently accepted theories regarding the formation of the Earth’s crust and mantle.
The expedition planned to drill at a site on the South West Indian Ridge in the Indian Ocean, known as ‘Atlantis Bank’, where they believe conditions are optimum for this challenge. Water depth is very shallow – only 700 m – which enabled the team to drill relatively quickly, and geological faults have removed the upper ocean crust entirely; hence the Moho here lies at only about 5km below the seafloor.
Using the latest high-tech drilling equipment during the two-month IODP Expedition 360, the team aimed to drill at least 1.3km below the seafloor to start to explore how the lower crust is generated, and how far seawater penetrates at depth.
Does the Moho in the ocean really represent the crust-mantle boundary?
The team proposes that rather than representing the crust-mantle boundary, the seismological Moho may instead represent a serpentinisation front - the lowest point at which seawater has seeped into the mantle through cracks, transforming the mantle peridotite into serpentinite. The seismic characteristics of the crust and serpentinite are essentially the same, so seismology alone cannot distinguish them.
How deep can life exist in the Earth subsurface?
The serpentinisation of peridotite generates hydrogen and methane, both of which are fuel for microbes. If serpentinite exists deep in the Earth’s interior, then life may also exist in these extreme areas. How much life is down there, and what are the limits of this life? These are important questions which the expedition will try to answer.
They will return to the site at a later date to deepen the hole and eventually hope to achieve the ultimate goal of drilling a ‘Mohole’ right the way through the crust and into the mantle.
Further details of the expedition can be found at: SW Indian Ridge Lower Crust and Moho
Educationalists on board the JR on this and earlier cruises have put together resources for a variety of ages. These can be accessed at: JOIDES Resolution