© AL GRANBERG
| 1 | Deep-sea, manned submersibles and remotely operated vehicles collect fluid samples that exit natural points of access to the oceanic crust, such as underwater volcanoes or hydrothermal vents. These samples contain microbes living in the crust beneath. |
| 2 | Drilling holes into the Earth’s crust allows retrieval of rock and sediment cores reaching kilometers below the surface. The holes can then be filled with monitoring equipment to make long-term measurements of the deep biosphere. |
| 3 | Deep mines provide access points for researchers to journey into the Earth’s continental crust, from where they can drill even deeper into the ground or search for microbes living in water seeping directly out of the rock. |
| Oceanic Crust | Continental Crust | |
| Thickness | 6–10 kilometers | 30–50 kilometers |
| Area | About 60 percent of Earth’s surface | About 40 percent of Earth’s surface |
| Age | Rarely more than 200 million years | Up to 4 billion years |
| Water content... |
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