Cheap, capable of being made into any conceivable shape, strong and durable, plastic is something of a wonder material. It has proved so useful to humans that since the 1950s we have produced an estimated 8.3 billion metric tonnes of the stuff.

However, the victim of this success appears to be much of life on Earth. And humans, one day, could find themselves among them.

For some 79 per cent of the plastic produced over the last 70 years has been thrown away, either into landfill sites or into the general environment. Just nine per cent is recycled with the rest incinerated.

This has been described as "an uncontrolled experiment on a global scale" by scientists.

How much plastic is in the sea?

With more than eight million tonnes going into the oceans every year, it is estimated there will be more plastic than fish by 2050 and 99 per cent of all the seabirds on the planet will have consumed some. It is thought the sea now contains some 51 trillion microplastic particles – 500 times more than stars in our galaxy.

It is found all over the planet, with 300 billion pieces in the once-pristine Arctic and a remote island in the Pacific, the uninhabited Henderson Island, one of the Pitcairns, believed to have the highest concentration of plastic pollution in the world.

Is it dangerous?

Some plastic is toxic and it can disrupt hormones crucial for a healthy existence. Even when it is not dangerous itself – or not known to be – plastic acts like a magnet for a range of other poisons and pollutants we have spilled into the natural world.

To sea turtles, plastic bags in the water can look like jellyfish, floating on the surface plastic can appear to be a tasty snack for a seagull, based on millennia of experience, and to baby perch it appears more appetising than the plankton they are supposed to eat.

Unsurprisingly, gulping down all this indigestible poison instead of food is bad for their health. So far, it is known that marine litter harms more than 600 species amid what some regard as the beginning of the sixth mass extinction of life on Earth.

Why should we worry about pollution in the sea?

Killing off sea creatures is bad for humans because we consume so much of it ourselves. Some 92.6 million tonnes were caught worldwide in 2015, according to the United Nations' Food and Agriculture Organisation.

Given plastic degrades to pieces small enough to pass through the stomach into the flesh of fish and other animals, we are already eating some of the plastic we have thrown into the sea.

And, of course, just like other animals that plastic is likely to be finding its way into the tissues of our bodies with potentially harmful consequences.

What's being done about it?

The world is, finally, starting to wake up to the problem.

In February this year, the United Nations announced it had “declared war on ocean plastic”.

Thirty countries have now joined the UN’s CleanSeas campaign, including the UK, Canada, France, Indonesia, Sierra Leone, Brazil, Norway, Italy, Costa Rica, Kenya and Peru. The US, China, Russia and Japan have not.

The UK has banned microplastics in "rinse-off" cosmetics, like facial scrubs, but not "leave-on" products like make-up and suntan cream.

Any other problems I should know about?

Plastic may also be contaminating the air we breathe.

Plastic microparticles from cosmetics and microfibers from synthetic clothes are washed into the sewage system. While many pass through treatment plants and end up in the sea, others particles are caught up in sewage used to fertilise farmers’ fields. After it dries out, it may get picked up by the wind and blown about.

Professor Frank Kelly, an expert in environmental health from King’s College London, told a committee of MPs last year: “There’s a real possibility that some of those microparticles will be entrained into the air and they will be carried around and we will end up breathing them.”

Just how bad is it?

Perhaps not Earth-shattering, but definitely Earth-trashing. Plastic may end up being one of the defining characteristics of a new epoch in the planet’s history.

Eventually, the layer of plastic spread around the world from the 1950s onwards will form a noticeable line in the sedimentary rocks of the future.

And that is one reason – along with radioactive fallout from nuclear bomb tests, pollution, climate change effects such as higher sea levels, and the extinction of many animal species – that geologists are considering declaring the end of the Holocene and the beginning of the Anthropocene or the ‘Epoch of the Humans’.