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EARTH’S sixth great extinction event has already begun. Now science is calling for urgent action to prevent life as we know it going the way of the dinosaurs.

The first five “events” destroyed more than 75 per cent of this planet’s life.

Animals. Plants. Entire ecosystems. The fossil record reveals all were smashed by natural disasters such as asteroids.

It’s happening again: But this time the experts say we are the cause.

Life on Earth is dying at an unprecedented rate.

The journal Science reports more than 320 animal and bird species alone have vanished since the 1500s. Most other animal populations from among the more than five million species on our planet have declined by an average 28 per cent.

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One third of all life on Earth is now threatened or endangered.

Remember how we always predicted bugs would inherit the world?

That now looks to be wrong: Studies show these humble creepy-crawlies are among the worst affected with losses representing as much as 45 per cent of their populations in the past 35 years.

Only humanity has thrived: Our population has doubled in the same time frame.

Doomsday looms — without the comet.

What’s causing it?

Wars. Pollution. Hunting. Fishing. Farming.

And climate-change induced natural disasters.

The new all-of-science review by international biologists and palaeoecologists warns all are seriously undermining the ecological health of the planet.

And our struggling ecosystems will increasingly start to hurt humans.

Already the effects are increasingly obvious: The current Ebola outbreak is just one example.

WHAT’S HAPPENING NOW?

Bats. Birds. Monkeys. Even mice.

All are among species being forced out of their habitats and into ever-expanding human territory.

Some even thrive amid the rubbish or under the eaves of our sprawling suburbs.

With them come previously unencountered — or at least rare — forms of disease.

Beetles. Butterflies. Worms.

All are vital for the health — and reproduction — of plants.

Insects are responsible for the pollination of 75 per cent of the world’s food crops — yet they are the target of intense insecticide spraying and habitat-changing activities.

The loss of such small creatures is having a trickle-up effect.

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It’s not just the fertilisation of next year’s wheat, barley, corn and apple crops: There’s also the vital nutrient recycling and composting roles which keep soils productive.

Balanced invertebrate ecosystems are also a strong natural source of pest control. Without them, US farmers would have to spend an extra $5 billion each year on eradication programs, the study says.

Then there are the wars.

As fish stocks vanish in one area, fleets need to move to another. This is already the source of increasing tensions in the South and West China Seas.

Unhealthy habitats also can unsettle streams from their paths — if they’re not already dammed.

Justin Brashares warns in Science that declines in wildlife have been linked to economic and social stresses which lead to exploitative child labour practices and the proliferation of terrorism.

“Leadership must move beyond superficial reactions to elephant and rhino poaching and consider the complicated fate of the billions of people who rely on our planet’s rapidly disappearing wildlife for food and income,” his study concludes.

SIGNS OF THE SIXTH MASS EXTINCTION

This extinction event differs from others in the long history of our planet in one major way: It’s been brought about by the loss of major predators and herbivores through human interaction.

Scientists have a term for it: Anthropocene defaunation.

All previous extinctions have been driven by cataclysmic events (such as asteroid collisions or super volcanoes) or natural transformations (such as the impact of world-spanning ice ages).

The impact of this one — which is already affecting up to 33 per cent of all animals — will be equally severe.

“Where human density is high, you get high rates of defaunation, high incidence of rodents, and thus high levels of pathogens, which increases the risks of disease transmission,” said Stanford University Biology Professor Rodolfo Dirzo who helped produce the review for the journal Science.

The demise of the megafauna — such as giant kangaroos, woolly mammoths and giant sloths — as recently as some 20,000 years ago may just have been the start. Many anthropologists believe such beasts were easy meals to the newly organised and armed homo sapiens (us).

Then there’s the fate of the Tasmanian tiger and the passenger pigeon. One of the most recent additions to the extinct-at-human-hands list is the baiji freshwater dolphin of China.

More than 1000 species have been killed off in the past 200,000 years. The International Union for the Conservation of Nature keeps records of 20,000 more plants and animals classified as endangered.

Large animals remain at the forefront of decline: Now, it’s the ever-present tale of rhinos and elephants being slaughtered for their horns, lions and leopards killed for the thrill (and dried testicles), and whales hunted for the sake of tradition.

But the greatest threat comes from loss of habitat: Less space to roam means fewer offspring, which in turn results in less viable populations.

The loss of such large animals is having a trickle-down effect.

Kenya is cited as a case-study: After the kill-off of most of its zebras, giraffes and elephants — the nation has become overwhelmed by rodents gorging on the ungrazed terrain.

Professor Dirzo states this loss of animal diversity will most likely have a very harmful future impact.

“We tend to think about extinction as loss of a species from the face of Earth, and that’s very important, but there’s a loss of critical ecosystem functioning in which animals play a central role that we need to pay attention to as well,” Dirzo said.

Some 3.5 billion years of evolutionary experimentation is under threat and with it much of the knowledge which could improve our own futures.

After all, we still striving to unravel the secrets of spider webs, gecko toes and pigeon homing.

IS IT TOO LATE?

It can be done, they say. If we have the will.

Scientific American cites the example of the black-footed ferret. Merely seven of these little animals were still alive little more than a decade ago. Now they’re back from the brink. Similar stories can be found for critically endangered animals ranging from condors to salamanders.

Philip Seddon reports in the journal Science that human efforts have saved 424 species of plants — mostly through careful cultivation and moving them to new areas away from human activity.

We’ve also seen — in the abandoned landscape around Chernobyl and the deliberate attempts to reforest the US eastern seaboard — that woodlands return (along with all their associated life) when farms and towns are abandoned.

But it remains a task requiring willpower from among general populations, government and industry.

There is no point saving animals without preserving the habitats within which they would live, the study says.

Reintroducing animals to unbalanced habitats is one tactic the study supports. Whether through introducing new predators to fill a vacated niche, or through genetically rebuilding lost animals, such stability has a cascade effect on the survival of other local animals, plants and trees.

How long do we have?

A study published by Nature in 2011 says we have just a century to change our ways before the “tipping point” is reached that will guarantee mass extinction.