Post date: Jan 08, 2013 4:6:25 PM
A Japanese-led project aims to drill to the Earth's mantle, a 3000 kilometre-thick layer of slowly deforming rock between the crust and the core. In its early stages, the $US1 billion mission would deploy a drill just 30 centimetres wide to bore into the Earth's crust to bring back the first ever samples of fresh mantle rock.
AT SEA, OFF EAST AFRICA (POOL) - An ambitious $US1 billion mission to drill six kilometres beneath the seafloor to the Earth's mantle and bring the first ever fresh samples to the surface is being planned by geologists.
The Japanese government has invested heavily in the project through its funding of deep-sea drilling vessel Chikyu, first launched in 2002 and capable of carrying 10 kilometres of drilling pipes.The project, still in its planning stages, could answer some of scientists' biggest questions about the origins and evolution of Earth itself, with almost all of the sea floor and continents that make up the Earth's surface originating from the mantle. Geologists involved in the project are already comparing it to the Apollo Moon missions in terms of the value of the samples it could yield.
The geologists have identified three possible locations, all in the Pacific Ocean. Project co-leaderDamon Teagle, from the University of Southampton in England, says making a decision on where to drill is the most pressing concern.
"The first thing that really needs to be done is to decide where we would actually drill this hole because the technology that needs to be developed is going to be site specific and will need to be engineered for that specific site. So the next phase that we need to go through is a phase of site survey where we'll do intensive geophysical observations of the sea floor to make sure that we can image the crust mantle boundary," said Teagle.
The Earth's mantle is a 3,000 kilometre-thick layer of slowly deforming rock between the crust and the core which makes up the majority of our planet. The task will be all the more difficult for being conducted in the middle of the ocean, although it is here that the Earth's crust is at its thinnest, at around 6 kilometres compared to 60 kilometres on land.
Geologists will use a drill just 30 centimetres wide in their attempt to bore all the way from the ocean floor to the mantle, a monumental engineering feat. What makes the task even more difficult is that, currently, the drill bits have a limited lifespan of between 50-60 hours before needing to be replaced, meaning drilling could take many years unless technology improves.
Pointing to the tip of a drill head similar to that will be used in the operation Teagle explained: "They make a hole that's if things are going well is about 30 centimetres across and then would actually grind out a stump of core that's about six centimetres wide."
He added: "We use what is known as a rotary coring bit, which is adapted from the oil industry that is used for drilling very hard formations and also with scientific ocean drilling we generally like to take core rather than just using geophysical measurements down the hole to investigate what's there, so if we have the core then we can do chemical and physical experiments on the rocks and minerals that we collect."
The Chikyu drilling vessel has already set a world-record for the deepest hole in scientific ocean drilling history, reaching 2.2 kilometres into the seafloor.
Despite making up 68 percent of the Earth's mass, Teagle says scientists only have a "reasonable" idea of what the mantle is made of and how it works. He says the examination of mantle core could revolutionise our knowledge of the world's evolution.
"First one (priority) is to get fresh pristine samples of these mantle rocks and from that we will understand some basic things about the Earth that we don't know. How much water is in the mantle, how much CO2 is in the mantle, what phases does carbon exist in the mantle. We will know about the distribution of heat producing elements like uranium or potassium. We will also get information on how well mixed the mantle is and how the mantle has mixed over geological history," he said.
Recent geological discoveries of life forms found deep in the ocean crust have encouraged Teagle to believe that similar discoveries could be made in the mantle itself.
"One could imagine that if we had a fault zone that goes very deeply through the ocean crust, where's there's cold seawater penetrating deeply into the ocean crust, that perhaps we have life at very great depths in the ocean crust and possibly, and I say possibly, maybe even into the upper mantle," he explained.
If Japanese support can be combined with other funding Teagle says they could start drilling before the end of the decade, making it possible for humans to finally reach the Earth's mantle by the early 2020s.
The first attempts to reach the Earth's mantle actually began back in the early 1960s. Dubbed 'Project Mohole' after the Croatian meteorologist Andrija Mohorovicic who first discovered the boundary between the Earth's crust and mantle, a team of U.S. scientists managed to drill a few metres into the oceanic crust off Guadalupe Island in the eastern Pacific. The project was abandoned amid spiralling costs.