Was the Cambrian period (538-486 million years ago) the most significant in the history of Life? [1] Was there really a kind of biological explosion where simple single celled creatures suddenly transformed them selves into complex multicellular beasts with nervous systems, eyes, guts and feeding strategies? It’s always been a bone of contention with some shouting emphatically “yes” and others being a little more sceptical. “Sampling bias”, they say: correctly adducing that there were plenty of multicellular creatures in the Pre-Cambrian, it’s just very difficult to find their remains.
Now the proponents of the Big Change Theory have found their case strenghtened. Recent research. described here by Kate Ravilious for the Guardian, suggests a natural mechanism which drove the changes and caused a sudden leap in the diversity of life. According to Kate
changes in solar energy caused climatic changes that altered the amount of weathering of land surfaces – especially at high latitudes – with periods of fast weathering releasing bursts of nutrients into the oceans, which drove photosynthesis and pushed up oxygen levels, fuelling the high speed evolutionary changes. [3]
And the interaction of these changes in solar output with variations in the earth’s orbit would explain the timing and nature of these sudden leaps for life.
And our take? Something happened around Cambrian times, gentle readers-there really is a step change, as shown by the appearance of shells, backbones and all the other markers of our modern phyla. And the idea of a coinciding, plausible mechanism is persuasive indeed. However as veterans of the paleontological wars we have a few questions. Did the Cambrian explosion a generate an increase in total biomass, or just complexity of forms? If this pattern of solar cycles and variable orbit repeats every two or three million years, why have we not seen at least one comparable event since (500 million years is a long time) Were there no volcanoes, tectonic plates or asteroids to muddy the waters in the Cambrian, the way they did in the Permian or Cretaceous, for examples? We love the Cambrian explosion and the way it has driven curiosity and much good research. But like every Big General Idea-in science , history, psychology, whatever- we see them more as pointing the way to more research, not a final answer.
[1]https://en.wikipedia.org/wiki/Cambrian
[3]https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025GL118689
#evolution #paleontology #cambrian #precambrian #solar cycle #earth orbit #fossils
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