Jul 27, 2017

Earliest Known Evidence of Life Confirmed in Jewel-Studded Ancient Rock

Close-up of Isua, Greenland rock that contains garnet crystals. New research supports the claim that the black bands seen in the image are the remains of organisms that lived 3.7 billion years ago.
Greenland’s freezing temperatures make it an unlikely candidate for early explorations of life. But, a rock from Isua, West Greenland — called the Isua Greenstone Belt —contains the likely remains of Earth’s oldest organisms, according to a study published in the journal Nature.

“We cannot say exactly when life began on Earth, but we can now say with much more certainty that it existed 3.7 billion years ago,” lead author Tue Hassenkam said. “We can also say for sure that the microbes were living in a marine environment, since the biological remains must have precipitated onto the bottom of an early ocean.”

Hassenkam, an associate professor at the University of Copenhagen’s Nano-Science Center, along with senior author Minik Rosing of the University of Copenhagen and several colleagues utilized a groundbreaking high-tech method to study the Greenland rock. Hassenkam likened the effort to a blind man feeling the pavement in front of him with a stick. In this case, the "stick” was a very sharp laser needle emitted via a process called Atomic Force Microscopy (AFM).

“AFM can feel down rows of single atoms,” Hassenkam explained. “By varying the wavelength of laser light, we could ‘feel’ how the surface responded. The response depends on the chemical bonds in the surface at that spot.”

Isua, Greenland rocks from which the garnets and their inclusions were extracted. The layered structure, which was once horizontal, shows that the rocks used to be part of the bottom of an ocean. The dark stripes are where researchers found the garnets and their inclusions that contain what are believed to be the earliest known remains of life on Earth.
The technique allowed the researchers to determine with nanometer precision where the various building blocks of life were distributed within the Isua Greenstone Belt. These included carbon, oxygen, nitrogen, and a form of phosphate. They were lacking one important building block, however: hydrogen.

The researchers later determined that hydrogen is so small — it is the lightest chemical element — that it must have seeped through the rocks. Its absence actually provides evidence that the samples were not contaminated by more recent biological material.

What they did find, by way of the other elements, were “remains of early life trapped inside inclusions inside garnet crystals that grew in a sedimentary rock, and included parts of the sediment as inclusions,” Rosing said. “The materials inside the inclusions were part of the sediment, which formed more than 3.7 billion years ago.”

That age has previously been confirmed by a barrage of dating methods, with measurements of the decay of uranium-to-lead providing the most definitive, precise information.

The researchers believe that the identified life-associated chemical elements within the rock are the remains of single-celled organisms, possibly bacteria. These elements are “still tightly bound to each other within the scale of single-celled organisms inside the garnets,” Rosing said.

Earlier studies speculated that remains of early life could be found in the Isua Greenstone Belt. The new research not only confirms such prior speculations, but also pinpoints what these remains consist of with greater clarity.

Isua rock formation in western Greenland.
Greenland turns out not to have been a particular hotbed for life back in the day. The discovery of the earliest probable known evidence for life happened in the Greenland rocks more as a result of good preservation in the Arctic environment.

“The rocks have recently been scoured by the Greenland Ice Sheet and have little or no vegetation,” Hassenkam said, indicating that this lack of other natural materials allowed the rocks to better preserve and show their earlier, ancient inclusions.

“We did something similar to what is portrayed in the movie ‘Jurassic Park,’” said Rosing, “but with the difference being that our time capsules were not amber, but garnet, and our samples were 50 times older and, instead of mosquitoes, we had single-celled organisms.”

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