Scientists may have discovered evidence of the deepest microbial life ever found on the planet, detecting the presence of organic matter in rock fragments spewed up by mud volcanoes near the deepest place on Earth, the Mariana Trench.

While researchers are hoping to find signs of alien lifeforms lurking under the surface of Jupiter's moon Europa and Saturn's moon Enceladus, the discovery highlights the possibility that equally strange and unknown organisms dwell hidden on Earth, buried as far as 10 kilometres (6.2 miles) below the sea floor.

"This is another hint at a great, deep biosphere on our planet," lead researcher Oliver Plümper from Utrecht University in the Netherlands told National Geographic.

"It could be huge or very small, but there is definitely something going on that we don't understand yet."