Commentary | The conversationalist: The universe in a billion-year-old rock

How paleontologists look below their feet to learn about the solar system

Why do humans feel we must travel far to solve life’s mysteries? Can a car, train, or spaceship take us, by physical displacement of hundreds or thousands or hundreds of thousands of miles, to some undefined location of answers?

Talking to Hans Hofmann, Paleontologist and adjunct professor in the Earth and Planetary Sciences department at McGill, I learned that this is not the case: we need not look farther than beneath our feet. Holding a Precanbrian fossil I experienced, quite literally, William Blake’s mystical ability “to see a world” – nay, the solar system – “in a grain of sand.”

Between layers of sedimentary rock, scientists like Hofmann look for evidence of carbon, and for trails or imprints of once-living material that can, amazingly, furnish historical information about the ancient Earth, the sun, the moon, and other planets in our solar system.

“Time works like heat,” says Hoffman. Layers of matter cement on top of one another, the hydrogen and oxygen reacting with the environment are slowly dissociated from the organic compounds and slowly but surely all that is left is the permanence of carbon: “Charred carbon, like an egg you fried for much too long.”

The sun and its power

Hofmann shows me a microscope slide patterned with filaments and coccoids: cyanobacterial colonies from 1.8-billion years ago.

“Cyanobacteria, scum, the messy goo that sits on the shallow sea bed spreads out across the expanse of the sea floor and fixes energy from the sun. It reminds me of how it looks after the rain when a green crud forms along the ground – a green film. Minerals then precipitate out of the ocean, which harden with time and entomb all these organisms,” Hofmann says.

Paleontologists then cut tiny layers out of the indurated material and grind down the sample until it is transparent, and can be investigated under the microscope. On this particular slide, a thin layer of darkly pigmented cells had grown along the top of the colony indicating that these cyanobacteria of the Precambrian period protected themselves against ultraviolet light, as do cyanobacteria of today.

Although these slides prove a certain consistency in the sun’s activity over the past few billion years, astrophysicists have shown that the modern-day sun that we know and appreciate is much brighter than the sun that once was: billions of years ago, the sun had only 80 per cent of the luminosity it has today.

The moon and its height

Next, we look at a tidally influenced, rhythmically laminated mudstone from the approximately 620-650-million year old Elatina Formation in South Australia.

It was a burgundy colour with dark stripes unevenly spaced along the polished rock surface: these stripes indicated the monthly tide patterns of long ago. Stripes, much finer and fainter, filled the space between these dark stripes, recording to the individual day, the movement of the tides.

The precision of information we can get from a rock is amazing. Further, since it is the proximity of the moon to the earth that determines the strength of the moon’s pull on the earth’s waters, an analysis of these types of rocks tell scientists that, in the Precambrian period, the moon was closer to the earth than it is today.

Mars and its life?

The next great challenge for astrobiologists will be to determine if there is, or was, at one point, life on other planets. For this task, they will need to employ micropaleontological methods to determine whether in fact a particular microstructure was living, or simply made of organic matter.

“Organic does not mean biologic,” Hofmann explains. In other words, being made of organic matter is not sufficient evidence for life, the thing must also must contain other biological signatures to be considered “living.”

He shows me the fossil of a curling entity, that was deceptively worm-like, but which in reality was no more than mineral residues. Since the simple organisms that existed in the Precambrian period are the most likely to resemble extra-terrestrial organisms, astrobiologists can compare fossils from mars to those fossil records of verified biological material on earth. Without these paleontological records, one might mistake a drop of oil for a drop of life.

This information could not have been procured by the most successful space expedition. A glance toward our earthly insides was all it took. We learn about heavenly bodies as they were billions of years ago, but right between the buried layers of this good old planet of ours.

Rosie’s column appears every other Thursday. Send your grains of sand, curly fossils, and all your thoughts on life to theconversationalist@mcgilldaily.com.


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