Old Fossils and New Evidence for Early Life

Fossils Help Pin Down When Life Formed

fossils

Hematite tubes from the hydrothermal vent deposits in Quebec, Canada that represent the oldest microfossils and evidence for life on Earth. The remains are at least 3,770 million years old. Credit: Matthew Dodd, UCL

Life formed on our planet some 3.8 billion years ago, likely in a warm, wet environment. It left behind fossils as proof of its existence. Knowing where life blossomed and exactly HOW long ago it happened has always been a moving target. We have to look for very old rocks, fossils, and even chemical evidence for the processes that define life.

The oldest life forms on the planet were all one-celled organisms. They flourished in the ancient oceans, attracted to hydrothermal vents (volcanic vents that spew mineral-rich and super-hot water from under the seabed). Now, teams of scientists have found ancient fossil evidence for life dating back possibly as far as 4.3 billion years ago.

What did they uncover? Tiny filaments and tubes formed by primordial bacteria that lived by eating iron. The rock layers where they were found lie in northern Quebec, Canada. These sedimentary rocks laced with quartz likely formed in the region of deep sea vents. The tiny life forms actually created little mounds of sediment that became fossilized.

Life and Its Habits

Life is a funny thing. Our planet is teeming with it, and evidence for it lies everywhere. It can be something as complex as the radio signals and light pollution we send streaming out to space, or as simple as the tiny hematite tubes left behind by one-celled animals. Like the investigators in the TV series CSI say, you just have to follow the evidence to figure out how that life lived and when. The existence of earliest life can tell us a lot about the conditions on Earth when it existed. These rocks, with their tubules and mineral formations, are clear evidence of primitive life

Life Changes a Planet

Other rocks on Earth also tell a tale of how our planet got its oxygen, as a by-product of life forms producing oxygen. These photosynthetic cyanobacteria took the carbon dioxide and other materials as part of their food chain. In return, they released oxygen. Much of the oxygen combined with dissolved iron in the oceans, which then settled into layers of mud that eventually hardened to stone. Iron oxides formed thin layers called “banded iron layers”. They exist around the world and tell a silent tale of life changing its environment (as it has done throughout history).

The recent discovery in Canada is now helping people pin down the dates of life’s earliest emergence with much more precision. It will be interesting to see if the researchers will find other, earlier rocks with evidence for ancient life forms showing up and evolving along with our planet.

Want more info about the Canadian find? Check out this article or the research paper in Nature.

Cosmic Life: Our Search for ET

Life Elsewhere in the Universe?

does cosmic life exist on worlds like this

An artist’s concept of Kepler-62f, a super-Earth-size planet in the habitable zone of a star smaller and cooler than the Sun. Could places like this harbor life? Credit: NASA/Ames/JPL-Caltech.

Cosmic life: it’s a fascinating topic that comes up as soon as I mention I’m interested in astronomy and space. A couple of weeks ago I participated in an interview with Taia Handlin, who used it to create a podcast as part of her Biology of the Blog series. During our conversation, which was quite wide-ranging, she asked me about cosmic life — that is, life elsewhere in the universe and whether I believed it existed.  It’s a fair question. I told her that I do think there’s life elsewhere in the universe, although I wouldn’t characterize it in the realm of “belief”.  We don’t have evidence — yet — about actual life “out there”, but that evidence can be found as we do more exploration.

The Evidence for Cosmic Life

So, what IS evidence of life and its prevalence in the universe?  We only have one example of life in the cosmos, and that’s right here on Earth, with its many and varied life forms. So, we can be forgiven a bit for  thinking that we have a lot of evidence already. Or that we just have to look for conditions that created our kind of life, but in other places.  Of course, the reality will be quite a bit broader than our current perception.

The standard mantra has been to look for habitats that offer life what it needs: water, warmth, and food. Those are very general requirements, and we know that life has managed to exist in some pretty hostile environments. That’s what the science of astrobiology is designed to figure out — just what the conditions really ARE that would be favorable to life. Through their efforts, astrobiologists may well expand our definitions of cosmic life and where it can exist.

The first steps in understanding the chances for life besides here on Earth are to understand all the conditions under which it thrives here. There are places on our planet that mimic (or are very similar to) places on Mars, for example. If life can exist in those regions, then could it exist on Mars, too?  That’s a fair question, and I suspect we’ll be able to answer it more fully when we actually get to those Martian places and see for ourselves if life is there. Or was in the past.

Also, too, we need to recognize that some forms of cosmic life may not need conditions like these on Earth to survive. That’s what drives inquiry into the possibility of life on such places as Europa (which is subject to Jupiter’s gravity and radiation belts) and Titan. Heck. And, beyond our solar system, astronomers are finding worlds that exist in regions around stars, places where the conditions might be ripe for life to form (or have formed at least once). Finding those exoplanets, determining if they have life, and understanding their life forms (if they have them) will be a major step in determining the prevalence of life across our galaxy. I suspect that we’ve been very conservative in our definitions of life and the places it inhabits. That’s understandable — you have to put some constraints on your working definitions, and the beauty of science is that it’s self-curing. That is, once we find something that goes beyond our definitions, we can adjust those definitions and our theories to accommodate actual data points.

So, there may well be life out there. We just haven’t found it yet. That’s what I think is going on.

In Carl Sagan’s book Contact (and in the subsequent movie) when Ellie Arroway asks her dad if there’s life out there, he responds by saying, “The universe is a pretty big place. It’s bigger than anything anyone has ever dreamed of before. So if…it’s just us… seems like an awful waste of space. Right?”

That’s how I answered Taia in our interview, because as soon as I read that in the original book by Carl Sagan, it resonated with what I’ve felt all along — life is out there, waiting to be discovered. And, I don’t think a cosmos that has evolved to let us perceive it would have only one incidence of beings with eyes, ears, and brains to figure it all out.