It sounds like a simple question – what is the time? But look closer and you realise time is a slippery concept that scientists still do not fully understand. Even though we now have atomic clocks that can keep time to one second in 15 billion years, this astonishing level of accuracy may not be enough. The complexity of computer-controlled systems, such as high-frequency financial trading or self-driving cars which rely on the pinpoint accuracy of GPS, could in future require clocks that are even more accurate to ensure everything runs ‘on time’.

But what does that even mean? As Anand Jagatia discovers, time is a very strange thing. He visits the origins of modern time-keeping at the Royal Observatory in Greenwich and meets scientists at the National Physical Laboratory who have been counting and labelling every second since the 1950s. He meets Demetrios Matsakis, the man who defined time and visits the real-life ‘Time Lords’, at the International Bureau of Weights and Measures (BIPM) in Paris to find out how they co-ordinate the world’s time and why the leap second is ‘dangerous’.

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From Chihuahuas to Great Danes, Mexican Hairless to Afghan Hounds, dogs are the most diverse mammal on the planet. There are currently over 500 recognised breeds worldwide with almost every conceivable combination of size, shape, coat, colour and behaviour.

But why are there so many different kinds of dog?

That's what listener Simon St-Onge in Quebec, Canada wants to know – and CrowdScience has taken up the challenge.

Presenter Marnie Chesterton heads to Sweden, a world-class centre of canine research, to sniff around for answers. She finds out how the grey wolf morphed into the vast variety of dogs we have today, and heads out on a moose hunt with one of Scandinavia's most ancient breeds.

But are dogs really as different as they seem on the surface? The dog genome is revealing more about man's best friend than ever before – and could now be the answer to understanding both dog and human health.

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(Image: Tika, the Russian-European Laika)

Modern Martian hunting involves looking for the tiniest evidence of life. But when presenter Marnie Chesterton found out that a scientist she was meant to be chatting to about cleanliness had previously worked for NASA, the topic of space bugs turned out to be too intriguing to ignore, especially when a CrowdScience listener asked us a question on a similar theme. Could Earth's microbes hitch a ride on our missions to Mars and colonise the Martian soil? As the European Space Agency's ExoMars venture gears up to launch a rover in 2020 that aims to find out whether there is, or has ever been, life on Mars, we head to the programme's clean rooms and Mars Yard - a giant planet-simulating sandpit - to find out. Marnie meets space engineers whose job is to prevent microbial contamination of Mars whilst creating robots that can find signs of life on the Red Planet. And she discovers that planetary protection is not all about remote aliens: Could tiny Martians have already arrived here on Earth via a meteoric hitch hike?

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Presenter: Marnie Chesterton

Producer: Jen Whyntie

(Picture: Mars from the Hubble Space Telescope. Credit: NASA)

To be healthy you need to be clean – or so we’ve thought throughout human history.

The dazzling array of antibacterial products that exploded onto the scene in the 20th century took things to the next level, with their promises of eliminating 99.9% of germs.

But could an obsession with cleanliness actually be bad for us? There’s a whole world of microbes out there: some make us sick, but others are essential for our health.

How do we tell the difference? Listener Younes’s question gives CrowdScience the chance to sift the good dirt from the bad, with the help of hygiene expert Professor Sally Bloomfield. Along the way we soap up our hands with schoolchildren in Mumbai, get knee deep in mud on an English farm, and find out why snuggling up to a cow might be a good idea.

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Presenter: Marnie Chesterton

Producer: Cathy Edwards and Marijke Peters

Is there a killer asteroid with Earth’s name on it? The dinosaurs ruled for many millions of years before coming to their violent end. Will humanity prevail or are we doomed to succumb like the dinosaurs? It’s a question that will keep you up at night. No wonder our listeners Zarin and Pablo wanted to know more.

To find out, Anand Jaggtia heads to Denmark to see first-hand the evidence for a giant asteroid impact, written into the rocks at Stevns Klint. And we will hear from scientists at Nasa who are keeping a careful eye out for asteroids on collision course with Earth. Also, we discover that asteroids have a lot to answer for, maybe even our own existence.

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Why can't we use energy from the waves of the sea to create all the electricity that we need? Listener Michael in Kingston, Jamaica wants to know. Living on a Caribbean island means he’s never far from the might of the ocean – so could it power his house?

Presenter Greg Foot heads to one of the world’s leading wave energy test locations, the coast of Cornwall in the UK, to find out. There, he witnesses the challenges of the marine environment, from metre high waves in a giant indoor test tank to being buffeted on a beach where a 25km cable runs beneath his feet to a grid-connected offshore test site. And find out if Greg’s plan to feel the power of the waves first-hand on a research boat works out – in the middle of winter, in the northern hemisphere.

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Picture: Waves, Credit: Oli Scarff/Getty Images

Most of us want to be nice. But is it all it's cracked up to be? It's a question that's been nagging at listener Tony in Illinois, USA, for over 25 years. While studying at university, the lecturer asked him whether competing or co-operating was the best strategy for success – essentially, does it pay to work together or should we sharpen our elbows and look after number one?

Nastaran Tavakoli-Far goes in search of answers. She talks to a local hero about why he puts his life on the line for others, and visits a neuroscientist to find out what happens in the brain when we help others. Her quest also leads her to question whether women really are the more co-operative sex and how an animal called a kudu might reveal how human co-operation evolved in the first place.

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(Image: John Cook from Hertfordshire Fire and Rescue Service. Credit: Anna Lacey / BBC)

How would a fourth dimensional being appear to humans?

"It would look just weird" is one way to answer the question 'How would a fourth dimensional being appear to humans?' But it's more complicated than that - theoretical cosmologist Andrew Pontzen describes how objects are viewed from one dimension to another, and how it might affect parking spaces.

Also on the programme: our panel of experts discuss bubble experiments, a theory that the Black Death was a virus, space elevators, algae as a biomass fuel, what affects the speed of digestion in our gut, a short definition of dark energy and the question is it true our DNA has alien properties?

With Helen Czerski, department of mechanical engineering, University College London; virologist Jonathan Ball, University of Nottingham; and cosmologist Andrew Pontzen, University College London.

Do you have a question we can turn into a programme? Email us at [email protected].

(Image: Stripes and points of light, one guess what a 4th dimension might look like, Credit: Thinkstock)

What effect does air travel have on the climate? That is the question listener Neil sent CrowdScience from New Zealand. If you have ever looked up at the sky and seen the wispy white streaks that airplanes leave behind, then you are looking at one of the major environmental impacts of air transport – contrails.

To find out more, Anand Jagatia goes on a journey through the rugged, lava-ridden Icelandic landscape with earth scientist Thor and discovers how both natural events like volcanic eruptions as well as man-made acts of terror can shed light on the environmental impact of aircraft. Plus, we meet a man who tailgates 737 airliners to measure their emissions.

Do you have a question we can turn into a programme? Email us at [email protected].

Where did the first viruses come from? They have the potential to wipe out life on Earth. But could life on Earth itself have evolved from the first viruses? Like the chicken and the egg, there are fierce arguments about which came first and rival scientists get quite cross about it all.

We take a dip into the primordial soup of creation and try to answer listener Ian's excellent question. Along the way, we revisit medieval plagues, travel to Texas to the largest urban bat colony in the world and take a walk through the dense mosquito-infested Ugandan forest that gave its name to the Zika virus.

Plus, we reveal how a virus is responsible for the placenta. No virus, no placenta; no placenta, no humans?

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This programme has been edited since broadcast to remove a brief reference to ‘bubonic plague’ being included in a list of viral diseases.

(Photo: HIV viruses attacking a Cell. Credit: ThinkStock)