In last month’s celebration of Earth’s Pageant of Evolution I touched on the interplay of tectonics, geochemistry and archaic life. The intimate love-making of Earth’s geology and biology – to put it poetically rather than scientifically.
Getting back to the science, scientists have learned about the why and how of various ocean-bottom structures that provide the catalyst between geochemistry and biochemistry, by helping bind basic molecules into complex organic building blocks of life.
This month to convey the immensity of Deep Time, I’m scaling down Earth’s 4.6 billion years to 24 hours. A billion years take 5 hours plus change, 3.2 million years tick by every minute. Our human story fits into Earth’s past 4-5 seconds. Imagine that.
Earth was an infant (3-4 minutes) when Theia slammed into her, creating our Moon/Earth system. By 3 a.m., baby continents were plowing through the oceans and doing their mountain-building, erosion, grinding, pulverizing, redistribution, redigesting, creation drama.
Suggestively the earliest simple-celled organisms show up shortly after that. Toughing it out in a very hostile world of raw unfiltered sun rays and energetic particle bombardment along with toxic atmosphere and oceans.
To the rescue – plate tectonics started a cascade of processes – that by around 5 a.m. induced Earth’s iron core to turn into a dynamo that built a magnetic force field around Earth, thus deflecting those deadly particles. This allowed the slow seepage of geochemically produced oxygen to interact with the sun’s rays, which in turn allowed ozone to form and accumulate, absorbing ever more of those harmful rays.
As Earth’s shielding developed, life figured out how to utilize the tamed sunlight to split water’s H2O bond, using the hydrogen atoms to build sugars while discarding the oxygen. Thus photosynthesis, a potent source of oxygen, was born and Earth’s ozone shielding got reinforced. Still, the global ocean and atmosphere was a brew of toxins, though geology and biology was busy cleaning that up, albeit at a glacial pace.
Geology acts very slowly. How slow is slow, you ask? Consider taking a trip around the world, moving as fast as your fingernails grow. Worse, upon your arrival you collide and are sent reeling right back across the planet, again and again.
One result was that shallow seas and massive tidal pools existed for immense periods of time, coming and going. While continents were creeping along, archaic microorganisms within those oceans were reproducing every day, in hours and minutes.
By afternoon, some simple cells expanded, sequestering their command and control within a reinforced citadel (the nucleus), while creating new components, structures and pathways within the much larger fortified cell membrane. These cells even recruited outside microbes to help with the increasing work load and differentiating duties. Thus Earth’s first eukaryotes appeared.
In learning about this scientists made a fundamental realization: cell biology and organisms, their development and evolution, cannot be considered without also understanding the environment within which they exist, and to which they must constantly adjust in order to thrive.
So it was, by 3 p.m. eukaryotes were firmly established, pushing Life’s potential as far as the environment allowed. Then back to biding time, waiting for what came next as Earth continued going through its great geochemical and geophysical convulsions, including continent- grinding global ice ages.
By 7 p.m. ocean chemistry was moderating while free oxygen levels achieved concentrations that allowed those complex eukaryotes to evolve into coordinated communities and then into Earth’s first critters.
But it was a rough time. When communities of critters had a chance to develop and reproduce enough to make a difference, they made a difference, all right. They were too bountiful and sucked free oxygen right back out of their environments. Suffocating themselves into extinction, until stromatolites could pump out enough oxygen for another go. One day at a time.
Apparently, living in moderation never was part of Earth’s natural order. Of course, the consequence of this tendency towards excess has always been collapse.
So, around 9 p.m. and after some 17 hours’ worth of stage prep, developing various genetic widgets and gadgets like a Lego set, a few rehearsals, now the timing was right – Life took off like unchaperoned teenagers at a springtime full moon dance.
The Ediacaran “Explosion” lasting around 12 minutes before an extinction event handed Life’s baton over to about 7 minutes’ worth of the Cambrian “Explosion.” During this third of an hour most of Life’s basic animal body plans (Phylum) appeared, filling every available niche.
The apparent suddenness was even a dilemma for Charles Darwin, since this sudden fossil proliferation was already recognized back then. Today we understand it as an “eye of the beholder” problem. Looking through the wrong end of the telescope.
One hundred sixty years of collecting and processing evidence has resolved a time span of 70 million to 90 million years’ worth of biological adventurism. Geologically, it’s shockingly short. Biologically, not so much.
Why was the Cambrian radiation so exuberant? Short answer, Earth was ripe and Life was ready. There were no precedents. No competition. No rules. No constraints. Endless microbial mats on sea floors. Generations ticking away in geologic milliseconds.
As primal animals consumed all those microbial mats things started getting grim, competition was born along with its hunting and defense strategies. Next thing we see is an arms race and ecology developing as life settles in for the long haul.
Except for periodic massive catastrophic tectonic upheavals, or the occasional asteroid impact, knocking the pins out from under Earth’s biosphere.
When radical geophysical catastrophes have Life scrambling again, it returns to its ancient genetic toolkit. As the dust settles and survivors figure out what’s what, there are moments of sudden “explosive” (geologically speaking) animal radiation events.
Life would repurpose its genetic heritage, body plans adapted, animals radiated, and survivors learned to thrive in their brave new world. Some say since the Cambrian, Earth’s story has simply been variations on those themes as life dances to climate. But, all that must wait for another FCFP issue.