Discovering the origins of life

Andrew Czaja is a rock star.

The University of Cincinnati geology professor studies paleobiology – the study of ancient life. But what he’s also doing is uncovering evidence of the possibility of life beyond this planet.

He does it by studying rocks on Earth.

 “We need to understand what to look for other than aliens coming to Earth on a spaceship,” he said. “Likely, we are going to find a chemical signature of life or a single-cell type of organism. Those can be a challenge to find."

He’s not looking for living ones – those may have long been consumed by the elements. But he might find the remnants of life that show life once existed there.

We are not talking about dinosaur bones – those appeared on the Earth about 245 million years ago. Czaja is looking for fossils of microorganisms in rock, or their chemical signatures.

Scientists can trace life on Earth as far back as 3.5 billion years. There’s even some evidence it was present as much as 3.8 billion years ago.

“We look for evidence for life on the early Earth, fossils or chemical signatures and ratios of elements or isotopes,” he said. “We 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. We think that billions of years ago, Mars may have been like Earth.”

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

“It’s not like finding a dinosaur bone,” he said. “When I go out, I don’t know if I found anything because they’re too small to see.”

Czaja brings back rocks to his lab that he believes are old enough to have evidence of early life. He cuts extremely thin slices of the rock samples, the thickness of a human hair. He 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 is long gone – consumed by nature, and with it all signs of DNA. But the outer layer is sometimes preserved and is made of carbon molecules that are one indicator of life.

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.

“You need to convince people that what you found is a fossil of something that was living,” he said. “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. You find part of it.”

Geologists like Czaja must build a cascade of traits to provide stronger evidence of life.

“First you find (the artifact) in the rock,” he said. “Then you say what is this thing made of. If it’s a fossil of an organism, it’s made of carbon atoms, not just some brown mineral.”

Czaja uses a Raman spectrometer to identify the fossil. He has a HORIBA Scientific T64000 Raman system Triple Raman Spectrometer, a high-performance platform for Raman analysis.

“You can put your thin section with the fossil under the microscope attached to the Raman spectroscope and focus the laser on it. It gives me a spectrum of whatever material it is,” he said. “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.”

He can map the spectrum with the instrument and have the material spatially located. That creates a map of everywhere there is brown material, a carbon signature.

“I can show people that this whole thing is made of organic carbon,” he said. “With my machine, I can make a three-dimensional map.”

What’s preserved is the bacterium’s cell wall. The interior is mostly water with biochemicals and DNA, but that’s lost when it dies.

“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.”

Why does any of this matter?

Czaja and his colleagues are trying to understand the history of life on Earth. That leads to the exploration of life on other planets. The current mission to Mars, the Curiosity Rover, launched in 2012, is looking for environments that life could have existed. It is not looking for life itself, but instead places there was liquid water at some time.

“If you find water you have found a habitable environment. But it’s not looking for fossil evidence,” he said.

The hopes of scientists are to find areas that could have supported life in the past and eventually explore its geology to find evidence of early life.

This may happen with the next mission to Mars, called Mars 2020. It will search for evidence of ancient life and collect samples that will be brought back to Earth by a future mission. If Czaja is lucky, he may get to study these samples in his lab.

Czaja said the spirit of discovery is a very human phenomenon.

“I think it’s interesting to know where we stand in the universe,” he said. “We want to know the history of life on Earth. How life got started on Earth. And then are we alone? Is there other life on other planets? It’s a human desire to understand our origins and our place. So we look at our solar system.”

He believes if we do find evidence of life on other planets it will just be microbial life. If there was some complex life on Mars, he thinks we would have found that by now. We are also looking at the moons of Jupiter.

Czaja says it’s about knowing more about who we are and how prevalent life is out there.

“If we find evidence of life on Mars or any other place in the solar system, and it used the same biochemistry as it does on Earth, there would be a good chance we had a common origin. If it was different, it would have a different origin. That would tell us life could evolve very easily, and that is so, it may be prevalent throughout the universe.”

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