A beautifully clear and thoughtful account. "instability vs stability" is key point - it's not that (some) life can adapt to change and some not, but more the chaotic patterns of change that arise in periods of instability - meaning it's not just what kiinds of life can adapt, but how quickly can they adapt.
Thank you, that’s exactly the point I was hoping would come through. It’s less about “who can adapt” and much more about whether systems stay stable long enough for adaptation to happen. Once change becomes rapid and irregular, even well-adapted life runs out of time.
What was the order of cooling and volcanism? For example, was cooling itself due to a "Pinatubo winter", ie volcanic dust? Then you would have two events in succession, and linked.
Alternatively, does a two mile thick coating of ice cause increased faulting in thin areas of crust an thereby create new volcanism? Thus, cooling for long enough might give the one-two punch.
Unless all the Big Five were chance occurrences of multiple unrelated events happening near simultaneously. Thereby accounting for their rarity.
Great question, and this gets to why the Late Ordovician is still debated.
Right now, we don’t have the resolution to say whether volcanism caused the cooling, responded to it, or simply overlapped with an already unstable system. The mercury spikes point to volcanism close in time to both extinction pulses, but they don’t give us a clean sequence of events.
A short-lived “Pinatubo-style” cooling is unlikely to explain a long ice age on its own, which probably required sustained CO₂ drawdown. But volcanism could still have amplified stress by disrupting ocean chemistry and oxygen levels at critical moments. The reverse pathway you mention, ice loading affecting faulting and magmatism, is plausible in principle but very hard to demonstrate this far back.
What seems most consistent with the evidence is not a single trigger, but overlapping processes on different timescales. That kind of coupling fits the two-pulse pattern better than a linear cause-and-effect story.
Thank you for detailed discussion of all those causes.
It also reminds me of the planetary climate modes (hothouse - warm house - coolhouse -
Icehouse) which I understood as relatively stable regimes that can last for millions of years (and within them changes can still happen - like glacials and interglacials in icehouse regime)
How does it fit together with the instabilities of climate you are describing? Are these instabilities marks of change of planetary climate regimes?
A beautifully clear and thoughtful account. "instability vs stability" is key point - it's not that (some) life can adapt to change and some not, but more the chaotic patterns of change that arise in periods of instability - meaning it's not just what kiinds of life can adapt, but how quickly can they adapt.
Thank you, that’s exactly the point I was hoping would come through. It’s less about “who can adapt” and much more about whether systems stay stable long enough for adaptation to happen. Once change becomes rapid and irregular, even well-adapted life runs out of time.
What was the order of cooling and volcanism? For example, was cooling itself due to a "Pinatubo winter", ie volcanic dust? Then you would have two events in succession, and linked.
Alternatively, does a two mile thick coating of ice cause increased faulting in thin areas of crust an thereby create new volcanism? Thus, cooling for long enough might give the one-two punch.
Unless all the Big Five were chance occurrences of multiple unrelated events happening near simultaneously. Thereby accounting for their rarity.
Great question, and this gets to why the Late Ordovician is still debated.
Right now, we don’t have the resolution to say whether volcanism caused the cooling, responded to it, or simply overlapped with an already unstable system. The mercury spikes point to volcanism close in time to both extinction pulses, but they don’t give us a clean sequence of events.
A short-lived “Pinatubo-style” cooling is unlikely to explain a long ice age on its own, which probably required sustained CO₂ drawdown. But volcanism could still have amplified stress by disrupting ocean chemistry and oxygen levels at critical moments. The reverse pathway you mention, ice loading affecting faulting and magmatism, is plausible in principle but very hard to demonstrate this far back.
What seems most consistent with the evidence is not a single trigger, but overlapping processes on different timescales. That kind of coupling fits the two-pulse pattern better than a linear cause-and-effect story.
Thank you for detailed discussion of all those causes.
It also reminds me of the planetary climate modes (hothouse - warm house - coolhouse -
Icehouse) which I understood as relatively stable regimes that can last for millions of years (and within them changes can still happen - like glacials and interglacials in icehouse regime)
How does it fit together with the instabilities of climate you are describing? Are these instabilities marks of change of planetary climate regimes?
That’s such a great reading. The baseline matters way less than lack of stability!