The Sixth Mass Extinction: Are We Living Through a Biodiversity Crisis?

Earth has witnessed five mass extinction events over its 4.5-billion-year history. Each one reshaped life on the planet – from the Great Dying 252 million years ago, which wiped out nearly 96% of marine species, to the asteroid-driven Cretaceous extinction that ended the age of non-avian dinosaurs 66 million years ago. Now, scientists are debating whether we are living through a sixth – and this time, the driving force isn’t an asteroid or volcanic super-eruption. It’s us.

What is the sixth extinction?
Human activities driving extinction
Habitat destruction and land-use change
Overexploitation
Pollution and invasive species
Climate change as a compounding force
The Anthropocene epoch
Why it matters: the consequences of biodiversity loss
Food systems and agriculture
Medicine and scientific knowledge
Ecosystem stability and resilience
Irreversibility

What is the sixth extinction?

A mass extinction is defined as a geological interval in which at least 75% of all species on Earth disappear in a relatively short span of time. According to the WWF, the planet has experienced five such events, each triggered by natural forces entirely beyond any organism’s control. What scientists now call the Sixth Mass Extinction – also referred to as the Holocene or Anthropocene extinction – is different in one critical way: it is being driven by a single species, Homo sapiens.

The scale of current species loss is staggering. A landmark study published in Science Advances found that even under the most conservative assumptions, the average rate of vertebrate species loss over the last century is up to 100 times higher than the natural background extinction rate. Species that would have taken between 800 and 10,000 years to disappear under normal conditions have vanished within a single century. Current extinction rates are estimated to be between 1,000 and 10,000 times higher than natural extinction rates – rates that would prevail in the absence of human activity.

It is worth noting that not all scientists agree on the exact framing. A 2025 analysis published in Trends in Ecology & Evolution argues that while biodiversity loss is real and serious, the evidence does not yet meet the strict geological threshold of a mass extinction at the genus level across all groups. Researchers like population ecologist Leah Gerber caution that overstating the evidence risks undermining scientific credibility. This debate is about definitions and measurement, not about whether biodiversity loss is occurring – on that, there is near-universal agreement.

The 2019 Global Assessment Report by IPBES, produced by 145 scientists from 50 countries, put the situation plainly: around one million animal and plant species are currently threatened with extinction, many within decades. That figure represents an unprecedented level of biological crisis in human history.

Human activities driving extinction

Unlike past extinction events, today’s biodiversity crisis has identifiable, human-caused drivers. According to UNEP and IPBES, the five principal direct threats to biodiversity are: land and sea use change, direct exploitation of organisms, climate change, pollution, and invasive alien species – in roughly that order of impact for terrestrial ecosystems.

Habitat destruction and land-use change

Habitat loss is the single largest driver of terrestrial biodiversity decline. Agriculture alone is responsible for 90% of global deforestation and accounts for 70% of the planet’s freshwater use. Currently, 40% of all land has been converted for food production. As natural habitats shrink and fragment, species lose not only their living space but also their ability to migrate, find mates, and access food. Fragmented habitat patches cannot support the same species diversity as contiguous natural landscapes, and smaller, isolated populations are more vulnerable to disease and environmental shifts.

Overexploitation

Direct exploitation – hunting, fishing, logging, and the trade in wild species – is the dominant driver of biodiversity loss in marine ecosystems and a major factor on land. The IPBES sustainable use report warns that unsustainable exploitation threatens the survival of one million species and the livelihoods of billions of people who rely on wild species for food, fuel, and income. Overexploitation strips ecosystems of key species before natural population recovery mechanisms can compensate.

Pollution and invasive species

Pollution – including pesticides, heavy metals, plastics, and industrial chemicals – degrades habitats and poisons organisms directly. Nitrogen deposition from agricultural runoff is one of the most serious threats to terrestrial biodiversity, triggering cascading ecological effects. Meanwhile, invasive alien species, facilitated by global trade and travel, have been a major factor in 60% of all recorded extinctions. Humans have introduced more than 37,000 invasive species into biomes worldwide, costing the global economy more than $423 billion annually.

Climate change as a compounding force

Climate change is not just a future threat – it is already amplifying every other driver of extinction. Rising temperatures alter species’ ranges, disrupt migration and breeding cycles, bleach coral reefs, and make habitats inhospitable faster than many species can adapt. Research indicates that if all currently threatened species were to go extinct within this century, we could reach mass extinction thresholds comparable to past events within 240 to 540 years – an alarmingly short window in geological time.

The Anthropocene epoch

The scale of human influence on Earth has led scientists to propose an entirely new chapter in geological time. The term Anthropocene – derived from the Greek anthropo (human) and cene (new) – was coined by biologist Eugene Stoermer and popularized in 2000 by atmospheric chemist Paul Crutzen. It describes the period in which human activity has become a dominant planetary force, reshaping geology, climate, and life itself.

Officially, we still live in the Holocene epoch, which began roughly 11,700 years ago. The Natural History Museum notes that while it is widely accepted that humans have had a lasting and potentially irreversible influence on Earth’s systems, the International Commission on Stratigraphy voted in 2024 to reject the formal addition of the Anthropocene to the Geological Time Scale, primarily because its sedimentary record was considered too shallow and recent. Despite this decision, the term continues to be widely used in science, policy, and public discourse – precisely because it captures something real and urgent.

The markers of the Anthropocene are visible across Earth’s systems. Plutonium from nuclear tests appears in sediments worldwide from around 1950. Nitrogen from synthetic fertilisers saturates soils globally. Carbon dioxide concentrations in the atmosphere have risen to levels not seen in at least 800,000 years. Researchers examining Crawford Lake in Canada found that its sediment layers since 1950 captured precisely these anthropogenic signatures – nuclear markers, fertiliser nitrogen, and fossil fuel ash – demonstrating just how clearly and rapidly humans have altered planetary chemistry. Whether or not the Anthropocene becomes a formal geological epoch, its conceptual value is clear: it forces us to reckon with the fact that human civilisation is now a geological-scale force.

Why it matters: the consequences of biodiversity loss

Biodiversity is not simply an ecological metric – it is the foundation that sustains human life. As UNDRR explains, biodiversity underpins ecosystem services such as pollination, climate regulation, water purification, and nutrient cycling. Lose enough species, and these services break down in ways that directly harm human health, food security, and economic stability.

Food systems and agriculture

An estimated 75% of global food crops depend on animal pollination – primarily bees, butterflies, and other insects. Ecosystem services like crop pollination and water purification are directly tied to the diversity of living organisms. As insect populations collapse – driven by habitat loss, pesticides, and climate change – the agricultural systems that feed billions of people face mounting risk. The loss of soil biodiversity, including microorganisms essential for decomposition and nutrient cycling, further erodes the productivity of the land.

Medicine and scientific knowledge

A significant proportion of modern medicines are derived from or inspired by natural compounds found in plants, fungi, and animals. Every species that goes extinct represents a permanent loss of biological information – genetic sequences, biochemical pathways, and evolutionary adaptations built over millions of years. That knowledge cannot be recovered once it is gone. Scientists emphasise that we focus too narrowly on species loss itself, while the more immediate crisis may be the collapse of populations – the functional units that actually deliver ecosystem services – even before species-level extinctions are formally recorded.

Ecosystem stability and resilience

Biodiversity acts as a buffer against environmental shocks. Diverse ecosystems recover more quickly from droughts, floods, disease outbreaks, and climate extremes than species-poor ones. As the IPBES Global Assessment warned, we are eroding the very foundations of our economies, livelihoods, food security, and health. The interconnectedness of species means that losing one can trigger cascading effects – trophic collapse, the spread of invasive species, and accelerating habitat degradation – creating feedback loops that drive further extinctions.

Irreversibility

Perhaps the most sobering aspect of the current crisis is its permanence. Past mass extinctions took millions of years for biodiversity to recover. As research from Berkeley’s Understanding Evolution project notes, there are still opportunities to reduce our impact and protect remaining species – but the window is closing. Unlike climate change, where reducing emissions can gradually lower atmospheric carbon, extinction is a one-way door. No conservation effort, however well funded, can bring back a species once its last individual is gone.

The path forward does exist. Expanding protected areas, reforming food systems, reducing greenhouse gas emissions, and curbing the illegal wildlife trade are all interventions backed by strong scientific evidence. The question is not whether solutions are available – it is whether the political and economic will exists to implement them at the speed and scale the crisis demands.

What do you think? If current extinction rates are already 100 to 1,000 times higher than natural background levels, at what point does the distinction between a “biodiversity crisis” and a “mass extinction” stop mattering for conservation action? And given that biodiversity loss is irreversible in a way that many other environmental problems are not, should it be treated as a higher policy priority than climate change – or are the two inseparable?

References

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Table of Contents

What is the sixth extinction? 🔗

Human activities driving extinction 🔗

Habitat destruction and land-use change 🔗

Overexploitation 🔗

Pollution and invasive species 🔗

Climate change as a compounding force 🔗

The Anthropocene epoch 🔗

Why it matters: the consequences of biodiversity loss 🔗

Food systems and agriculture 🔗

Medicine and scientific knowledge 🔗

Ecosystem stability and resilience 🔗

Irreversibility 🔗