Life outside of Earth just became much more likely, scientists say

Oldest fossil ever found on Earth shows alien life on Mars is likely

Scientists have discovered what they believe are remains of microbial bugs which are some of the earliest living organisms on Earth.

The tiny fossils - half the width of a human hair and up to half-a-millimetre in length - take the form of blood-red tubes and filaments formed by ocean-dwelling bacteria that fed on iron.

The team contends that these bear more than a passing resemblance to the networks of bacteria that live in hydrothermal vents-towering, crenellated structures, pictured above, that form in the deep ocean above the boundaries between tectonic plates, where superheated mineral-laden water spurts up from beneath the seabed. And if life could have popped up on Earth so early in its history, it's possible it did on other young planets with water on their surface - which bodes well for the prospect of life on Mars, at least in its ancient past.

"This will definitely come as a big surprise to the scientific community, no doubt about it", said Dominic Papineau, a geochemist at University College London in the United Kingdom, who led the work. The researchers' estimate that the microscopic fossils, which have a straw-like shape, are anywhere from 3.77 billion to 4.28 billion years old - making them the oldest fossils ever discovered.

Featured image: Redish rock from the Nuvvuagittuq Supracrustal Belt in Qu├ębec, Canada is in contact with dark green volcanic rock, representing hydrothermal vent precipitates on the seafloor. Similar fossils from Australia that come in at about 3.5 billion years old are generally accepted as legit, but anything older is still subject to scientific debate.

During an expedition there, Papineau helped find an especially old-looking lump of rusty rock called jasper, or haematitic chert (haematite is an iron-containing mineral).

Some have criticized the findings by pointing out that the rocks appear to to have been volcanically heated more recently, which makes the microfossils dubious. "Phosphorus is essential for all life on Earth", says Dodd.

Earth is thought to be about 4.57 billion years old.

'Epifluorescence imaging [microscopes that use fluorescence to generate an image] of modern vent samples has shown that cylindrical casts composed of iron oxyhydroxide are formed by bacterial cells and are undeniably biogenic. This is one of the leading theories for how life spawned on Earth, as opposed to other theories such as panspermia, which suggests life was deposited here by an asteroid or other rocky body that crashed into our home planet. Additionally, the structures were identified alongside graphite and minerals like apatite and carbonate, which are typically found in biological matter and associated with fossils.

"It provides us with this high degree of certainty that these structures are indeed, biological microorganisms that were living and thriving around hydrothermal vents billions of years ago", he says.

The find-which will face fierce scrutiny from other palaeobiologists-has other implications, too. "We already have evidence of water at the surface of the Earth by about 4.3 billion years ago".

"I'm skeptical about the interpretations in the paper", she said. These egg-shaped structures often contain fossilized remains preserved in this form and embedded in younger rocks. The creatures that live around hydrothermal vents are fundamentally different: no sunlight penetrates so deep into the oceans, so the food chains of such ecosystems are based on reactions between the dissolved chemicals that well up from the crust. "The individual lines of chemical evidence are not particularly strong, but put these together with the evidence from the filaments and one comes up with a pretty convincing biological scenario", he says.

"The reality is, we have no idea of how the structures formed or why", he said. The rocks' chemistry doesn't necessarily signal a location near a vent, he says.