The Miner's Canary or the Sixth Extinction

Note: This is an AI-assisted English translation of the original Portuguese post published on 23 October 2004 at Ciência ao Natural. The original text was written by Luís Azevedo Rodrigues and is reproduced here for archival and educational purposes.

About ten years ago, I was wandering through a bookshop in Edinburgh when I came across a book by one of the most important palaeontologists and evolutionary biologists still alive. "The Miner's Canary" describes the history of life on Earth through its mass extinctions — those catastrophic episodes that periodically wiped out a significant proportion of all living species on the planet.

The title is a reference to the old mining practice of using canaries as biological alarm systems: when the bird fell silent, miners knew that toxic gases were present and that they needed to evacuate immediately. The author, Niles Eldredge, uses this metaphor to argue that the current biodiversity crisis is a warning signal — a canary that is already falling silent.

The Five Great Extinctions

Throughout the history of life on Earth, there have been five major mass extinction events — moments when the diversity of life was dramatically reduced in a geologically short period of time:

1. End-Ordovician (~443 million years ago) — approximately 85% of marine species disappeared.
2. Late Devonian (~375 million years ago) — about 75% of species were lost, particularly affecting marine invertebrates.
3. End-Permian (~252 million years ago) — the most devastating of all: approximately 96% of all species on Earth were extinguished. Life came closer to total annihilation than at any other point in its history.
4. End-Triassic (~201 million years ago) — roughly 80% of species disappeared, clearing the ecological stage for the dominance of the dinosaurs.
5. End-Cretaceous (~66 million years ago) — the most famous extinction, which ended the reign of the non-avian dinosaurs, along with approximately 75% of all species.

Each of these events was followed by a long period of recovery and diversification — life always found a way to rebuild, to fill the ecological voids left by the vanished.

The Sixth Extinction

What Eldredge argues — and what many palaeontologists and biologists have since documented in far greater detail — is that we are currently living through a sixth mass extinction event. Unlike the previous five, this one is not being driven by an asteroid impact, a volcanic super-eruption, or a dramatic shift in ocean chemistry. It is being driven by a single species: Homo sapiens.

The rates of species loss currently observed are estimated to be 100 to 1,000 times higher than the natural background extinction rate — the baseline rate at which species have always gone extinct throughout evolutionary history. Habitat destruction, overexploitation, invasive species, pollution and climate change are the primary drivers.

The miner's canary is no longer singing.

Why Does This Matter?

One of the most important lessons that palaeontology offers us is a sense of deep time — the understanding that the history of life on Earth is incomprehensibly long, and that the processes that shape it operate on timescales that dwarf human civilisation. Mass extinctions, from this perspective, are not anomalies: they are a recurring feature of the history of life.

But they are also irreversible. Once a species is gone, it is gone forever. The evolutionary lineages that are being severed today will never be recovered. The ecological relationships that have been built over millions of years of co-evolution — the intricate webs of predation, mutualism, competition and parasitism that constitute living ecosystems — are being unravelled faster than we can document them.

Eldredge's book was published in 1991. In the more than three decades since, the evidence has only grown stronger. The canary is not just silent — it has fallen from its perch.

Original post published on 23 October 2004 on the blog Ciência ao Natural, hosted at the University of Campinas (UNICAMP), Brazil.