Raman Spectroscopy Uncovers Origins of Life in Ancient Samples

Is there life beyond earth? It’s a timeless question.

Now geologists are trying to solve that puzzle here on earth. To do that, they must use painstaking methods of exploration and Raman spectroscopy to reach their foundational conclusions.

That includes geologists like Andrew Czaja. Ph.D., from the University of Cincinnati. His area of specialty is paleobiology – the study of ancient life. He looks at slivers of rocks for evidence of the earliest life on earth. Most likely, those discoveries will come from the similarity of specimens we find here on earth and deep beneath extraterrestrial bodies. That’s Czaja’s focus.

Scientists have shown evidence of life on earth going back about 3.5 billion years. Some studies suggest it may go back as far as 3.8 billion years.

Czaja isn’t looking for ancient living organisms here on earth. Those have been dead for billions of years. He is looking for fossils of microorganisms in rock, or their chemical signatures.

He searches for evidence of life on the early Earth through fossils or chemical signatures and ratios of elements or isotopes in ancient rock samples. Scientists can use that knowledge of the early Earth and apply it to other planets, particularly Mars, because it’s the most similar place to Earth. It’s a widely accepted belief that billions of years ago, Mars may have been like Earth.

Czaja and his colleagues must study ancient rocks because it’s the only record of the early Earth.

Czaja collects rock samples that he believes are old enough to have evidence of early life. He cuts slices of the rock samples as thin as the thickness of a human hair. Czaja examines those slices for evidence of microscopic bacteria. He’s looking for fossil remains, many filled with minerals formed by the interaction of the rock and water. He also looks for a chemical signature that indicates life – carbon signatures left behind by the bacteria’s cell wall.

The interior of that cell has long ago been consumed by nature. And gone with it, is all signs of DNA. But the outer layer is sometimes preserved and is made of carbon molecules, which are one indicator of life.

Scientists must convince other scientists that they found a fossil of something that was living. If these bacteria were sitting in a rock for three billion years, they are not perfectly preserved. They don’t look the way they did when they were alive. Researchers find the remnants of the bacteria.

The trace evidence of bacteria is tiny. A very large bacteria cell would be the width of a human hair - it ranges from a few microns to a hundred microns in length. The bacteria are usually simple shapes - rod or spherical shaped. It doesn’t have many features for identification.

Geologists must build a number of traits to provide stronger evidence of life.

First, scientists must find the artifact in the rock. Then they describe what it’s made of. If it’s a fossil of an organism, it’s made of carbon atoms.

Czaja uses a HORIBA T64000 Raman system Triple Raman Spectrometer, a high-performance platform for Raman analysis to identify the fossil. He does it using thin strips of rocks he shaves off from larger pieces, so thin it becomes transparent.

“You can put your thin section with the fossil under the microscope attached to the Raman spectroscope and focus the laser on it,” Czaja said. “It gives me a spectrum of whatever material it is. Is it made of organic carbon, or something else? If it is made of organic carbon, I now have one more piece of evidence proving this thing was alive.”

The T64000 Raman system is a triple grating spectrometer instrument ideally suited for high performance Raman research. It maps the spectrum and spatially locates the material under study. That creates a map of everywhere there is brown material, a carbon signature. With that, Czaja can show other scientists that the sample is made of organic carbon.

“If it’s spherical, you should find a sphere of organic carbon. That’s difficult to do with a two-dimensional picture under a microscope,” he said. “Now you have a three-dimensional map of the morphology, more evidence that it was alive. Hopefully, you can find a whole population of them in your rock. That’s more evidence that it was alive.”

Czaja and others are trying to understand the history of life on Earth. The current mission to Mars, the Curiosity Rover launched in 2012, is trying to identify areas on the red planet that could have supported life. With the next mission to Mars, planned in 2020, researchers hope to explore the planet’s geology to find evidence of early life.

Czaja believes if we do find evidence of life on other planets, it will be microbial life. If there was complex life on Mars, he thinks we would have found that by now.

If evidence of life is found on Mars, and it uses the same biochemistry as on earth, it would suggest we have a common origin. If the biochemistry were different, that might mean it would have a different origin and suggest that life in the universe may be pervasive.