Life Before Fossils

Most of what we think of as fossils—old bones, hardened bits of plants, impressions of leaves—go back no more than 600 million years. Yet life on the planet is about 3.8 billion years old, more than six time further into the past. How do we know that? What evidence do we have of life on earth so much earlier than the oldest fossilized bones?

Stromatolites in Australia today, looking much as they did 3.5 billion years ago. (

Stromatolites in Australia today, looking probably much as they did 3.5 billion years ago.

One might think that there are older fossils that haven’t been found yet. But in fact there were no animals and plants at all before 600 mya. For about the first 3 billion years—much of the entire course of life on the planet—almost all life was tiny, even microscopic.

(One exception is fossilized stromatolites, hardened layers of bacterial cells piled in paddy-shaped colonies, seen today in their living versions at Shark Bay, Australia. Stromatolites thrived globally around 1.25 billion years ago but date back 2 billion years before that.)

Stromatolites in Australia, probably looking much as they did 3.5 billion years ago. (

Microfossils from 3.5 billion years ago (

So instead of digging through dirt, today’s paleontologists start by searching for the oldest rocks. Samples of rocks that formed up to four billion years ago from Australia, Greenland, South Africa and elsewhere are sliced, studied under a microscope, and tested with chemicals. Scientists find microfossils, tiny creatures’ cell walls that have mineralized into tough material. Or they find chemical smears of carbon or the products of the earliest photosynthesis. A recurring challenge is to figure out whether such traces are signs of early organisms or only part of the rock itself.

banded iron (

Banded iron (

A less direct but more common sign of early life is oxygen, especially as it appears in bands of rust in rocks. The same bacteria that built the stromatolites gave off oxygen as a waste product, most of which was absorbed by iron in the oceans. The result was masses of rust that eventually formed in bands in rocks, most abundantly around 2.4 bya. It wasn’t until 2 billion years ago that enough iron had turned to rust so that bacterial oxygen was no longer absorbed by the metal and instead accumulated in the atmosphere.

Who does this kind of ancient detective work? We’ve come a long way from Indiana Jones. The field today consists of hybrids of the disciplines that I’ve always been familiar with. For example, the curriculum in Geobiology at the California Institute of Technology includes the following course titles: Earth’s Biogeochemical Cycles, Isotopic Biogeochemistry, Microbial Metabolic Diversity, Paleooceanography, and Geobiological Constraints on Earth History.

As these titles suggest, the study of the history of early life parallels how we view ecology today: the state of living things is inseparable from the state of the planet; a change in one always means a change in the other, back and forth, continually.

Most of Your Cells Aren’t Yours

“All told, the [tiny] microbes in your body outnumber your own [much larger] cells by ten to one and can weigh as much as or more than your brain—about three pounds in an average adult. Each of us is thus both an organism and a densely populated ecosystem, with habitats harboring species as different from one another as the animals in a jungle and a desert.” Thus writes Stanford University microbiologist Nathan Wolfe in the 1/2013 issue of National Geographic. The more we find out about our bacteria, the more we might want to rethink who, biologically, we are.

Bacteria under a toenail. (

Bacteria under a toenail. (

The “habitats” that house these communities of bacteria and other microbes include our gums, guts,  genitals, underarms, inner elbows, tongue and throat, and the backs of our ears. Only a few species of bacteria make us sick. Others digest our food, make our vitamins, train our immune systems, moisturize and protect out skin. The bacteria that helps us digest milk crowd into the vaginal canal when a baby is passing through to help prepare it for breast milk.

There is an eerieness to me about all this. In many cultures people believe that their ancestors are always nearby, watching over them, helping or interfering with their lives. And devout Christians invoke deities, angels, and saints for assistance. So here for us secularists are our own ancient ancestors, the bacteria, every bit as with us and in us and influential as any holy spirit is thought to be.

What’s also eerie is that bacteria have a long history of becoming a part of other organisms, literally. Billions of years ago bacteria that could process light and excrete oxygen were absorbed into other cells and turned into the photosynthesizing chloroplasts of green plants. Other bacteria that boosted cellular energy were so useful to other cells that they became incorporated as the energizer mitochondria found in nearly all cells. In humans, bacteria don’t seem to have settled in as part of the furniture—yet—but they have been called “the forgotten organ.” Bacteria can be very good at making themselves indispensable.

We think of ourselves as a relatively new species, set off from the rest of nature by our brains. And indeed we are both new and different in some ways. But surely the way that bacteria have become integral parts of us, repeating a pattern billions of years old, reminds us what ancient creatures we really are.


Pope Francis on the State of the World

Pope Francis’ recent encyclical on the environmental crisis may be of as much interest to non-theists and naturalists as to Catholics and other theists. Laudato si (“Praise be to you,” a phrase from St. Francis of Assisi) describes interconnections among the problems in our world that I found valuable.

The lengthy document covers many topics, including climate change, biodiversity, the poor, our throwaway culture, and our profit-obsessed economy. But two themes stood out for me.

The first is Francis’ teaching that neglect of the environment and neglect of vulnerable people are essentially the same failing. This perspective is a radical turn; the Church has long taught that humans are separate from the rest of nature.

A sense of deep communion with the rest of nature cannot be real if our hearts lack tenderness, compassion and concern for our fellow human beings. It is clearly inconsistent to combat trafficking in endangered species while remaining completely indifferent to human trafficking. (paragraph 91)

We have only one heart, and the same wretchedness which leads us to mistreat an animal will not be long in showing itself in our relationships with other people. (92)

It is essential to seek comprehensive solutions which consider the interactions within natural systems themselves and with social systems. We are faced not with two separate crises, one environmental and the other social, but rather with one complex crisis which is both social and environmental. (139)

I have tended to think about environmental destruction and poverty as problems that, although related, are in different categories. But Francis integrates them, requiring us to raise our standards for our compassion.



A second theme concerns how we have arrived at the dismal state our world is in. We have made the mistake of believing that every new technology is a step in human progress. And we have gone further: We have accepted technological thinking as our way of relating to nature and people. We approach natural and societal problems alike through the scientific method, isolating the problem, solving it rationally and experimentally, taking charge, looking for mastery over it. As a result, our views are narrow.

The technocratic paradigm tends to dominate economic and political life. The economy accepts every advance in technology with a view to profit, without concern for its potentially negative impact on human beings. Finance overwhelms the real economy. Some circles maintain that current economics and technology will solve all environmental problems, and argue… that the problems of global hunger and poverty will be resolved simply by market growth. [Yet such people show] no interest in more balanced levels of production, a better distribution of wealth, concern for the environment and the rights of future generations. (109)

The specialization which belongs to technology makes it difficult to see the larger picture. The fragmentation of knowledge proves helpful for concrete applications, and yet it often leads to a loss of appreciation for the whole, for the relationships between things, and for the broader horizon, which then becomes irrelevant. (110)

Compelling as the Laudato si is, there are grounds for dissenting from its pessimism. After all, in recent decades the portion of global humanity living in extreme poverty has declined, not risen. The treatment of animals on farms and in labs in the U. S. has been improving. And the rate of human violent deaths has been dropping steadily throughout history. How are we to say whether things are getting better or getting worse for life as a whole on the planet? Would a reasonable answer be, some of both?

In the pope’s eyes, such uncertainty does not let us off the hook.

As often occurs in periods of deep crisis which require bold decisions, we are tempted to think that what is happening is not entirely clear. This is the way human beings contrive to feed their self-destructive vices: trying not to see them, trying not to acknowledge them, delaying the important decisions and pretending that nothing will happen. (59)

So what should we do? Francis’ recommendations include wider dialogue, the inclusion of a social perspective in every environmental act, and at bottom, a change in our hearts. But I also found good advice in his brief mention of the importance of learning “to live wisely, to think deeply and to love generously” (47).