Life on Earth a game of Jenga

Afew weeks back, I used the game “Cook the Goose” as an analogy for tipping points. When talking about species and extinction, another analogy would be “Jenga.”

The game involves removing pieces from a tower and stacking them on top but one never knows when pulling out a critical piece will cause the whole tower to fall down. It is a precarious balancing act fraught with the danger at each step.

Why species go extinct is a similar exercise. For the most part, no one is sure what causes an extinction event. What piece got moved resulting in the collapse of a population? Which event or events brought the whole thing crashing down?

Life on Earth has gone through many extinctions but there have been five mass extinctions events which wiped out at least 75 per cent of the species on the planet and as many as 95 per cent of the organisms. The end-Permian event, with 96 per cent of the species disappearing, is probably the closest we have come to the Earth becoming a lifeless mote in the darkness of space.

However, with the exception of the end-Cretaceous event which occurred over a relatively short period as the result of an asteroid strike, none of the previous mass extinctions are quick. Some have taken hundreds of thousands or millions of years in the geological record. Some have occurred because of life itself.

The last time life on this planet deliberately modified the atmosphere was likely the first major extinction event although it remains a subject of debate. Increasing levels of oxygen, produced through photosynthesis, changed the atmosphere and virtually destroyed a whole tree of life called the “Archaea”.

This past week, the International Union for Conservation of Nature (IUCN) released their red list for reptiles. It shows 1,829 species out of the known list of 10,196 species or 21.1 per cent are threatened with extinction. Previous red lists have documented amphibians (40.7 per cent), mammals (25.4 per cent), and birds (13.6 per cent) under threat.

We are changing the planet and while nothing we have done so far takes us into the category of mass extinction, we are playing a giant game of Jenga with life on Earth. And no one is truly certain what piece will cause the whole thing to come crashing down again.