Curious Kids is a series for children of all ages, where The Conversation asks experts to answer questions from kids. All questions are welcome: find out how to enter at the bottom of this article.

How do eyes grow? – Annette, age seven, Stratford-upon-Avon, UK

Thanks for this brilliant question, Annette. Human beings’ eyes are quite unusual, because they are almost full sized when we are born. They do grow a bit bigger – but only by a few millimetres. But that’s not all that happens – when we are very young, our brains also learn to make images from the messages it gets from our eyes, and that’s how we learn to see.

Let’s start at the beginning: before we are born, we grow inside our mum’s body. We start life being very tiny – about the size of the top of a pin, or a full stop in a book.

Even though we start out very small, we are made up of special tiny building blocks called cells.

Every day, the number of cells gets bigger and bigger, and different types of cell start to form as well.

The starting point

Each different type of cell is the starting point for the different parts of our bodies. So one type of cell might help to grow our ears, while another will help to grow our hearts, and so on.

There are three different types of cell that work to make our eyes. When we have been growing inside mum for about three weeks, our eyes start to be created.

After four weeks, special connectors called “nerves” start to grow, to connect our eyes with our brain. These connectors are very important, because they help our eyes to tell our brain about what we are seeing.

And by the time we have been growing inside mum for ten weeks, our eyes are fully formed, with all the parts they need in order to see.

At this stage, our whole body is about the size of a strawberry, so you can imagine how small our eyes must be. For the next 30 weeks or so, the baby will use energy from mum to grow bigger and bigger, until it is born.

Learning to see

When we are born, our eyes alone are about the size of a large raspberry. They don’t grow much bigger than that, and end up being about the size of a cherry.

In fact, when you think about how much bigger a grown up hand is than a baby’s hand, it’s clear that our eyes don’t have to grow very much at all, compared with the rest of our body.

What does change, though, is our sight. As soon as we open our eyes after we are born, they start to send signals along the nerves connecting to our brain.

But at first, we don’t see very well, and most things will look quite blurry. This is because our brain needs to learn how to turn information from our eyes into what we see.

As we get older, our vision gets better and better. When we are about eight weeks old, we can start to focus our eyes on the faces of people close to us. When we are three months old, we start to be able to follow things if they are moving around.

By five months old, we can see colours, and by the time we are three years old, we can see things just as clearly as most grown-ups.

It’s really important that we look after our eyes. We can do this by wearing sunglasses on bright days to protect our eyes from the sun, and by having our eyes checked over every year by an optometrist or eye doctor, so that we have clear sight long into adulthood.

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to us. You can:

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Please tell us your name, age and which town or city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question, but we will do our best.

More Curious Kids articles, written by academic experts:

• What existed before the Big Bang? – Ethan, age ten, Sydney, Australia

• What is a species? – Finlay, age four, London, UK

• How do moths eat our clothes? – Albie, age five, Australia

Hannah Bartlett, Reader in Optometry, Aston University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

This is an article from Curious Kids, a series for children of all ages. The Conversation is asking young people to send in questions they’d like an expert to answer. All questions are welcome: find out how to enter at the bottom.

We have eyes on the front of our heads so we can see where we are going, but birds’ eyes are on the side so how do they see where they’re going? – Thomas and Luke, age six, Sussex, UK

Dear Thomas and Luke,

Thanks for your question. First of all, I should mention that not all birds have their eyes on the sides of their heads. Pigeons and parrots do, but other birds, such as owls, have large eyes placed close together at the front of their heads – a bit like ours.

Whether they have eyes at the front or on the sides of their heads, all birds can still see straight ahead. But that doesn’t mean all birds see things in the same way. In fact, where a bird’s eyes are on its head can tell us a lot about how it sees the world.

Having two eyes means animals can see a three dimensional image of what’s around them. So they can perceive the height, width and depth of an object, as well as how far away it is.

Where a bird’s eyes are on its head affects its field of vision – that’s how much it can see in front and to the side at any one time. Think about how far you can see to either side without turning your head: these are the limits of your own field of vision.

Because owls have eyes at the front of their heads, they have a smaller field of vision – around 150 degrees for a barn owl (though they can turn their heads very far to look around).

Parrots, pigeons and other birds with eyes on the sides of their heads have a much bigger field of vision, of about 300 degrees. Amazingly, this means that they can see in front and a long way to the side, at the same time.

Where the eyes are placed decides how a bird views its surroundings using different types of vision. Binocular vision means both eyes focus on the same object at the same time, and eye movement is coordinated – this is the kind of vision that predatory birds such as owls rely on most.

Monocular vision means each eye is focused on a different object at any particular moment, and this is normal for parrots and pigeons. Having different kinds of vision helps different kinds of birds survive in the wild.

For parrots and pigeons, having eyes on the sides of their heads is a huge advantage. Having a wider field of vision with only a small blind spot behind them lets these birds see where they are going, while also keeping an eye out for predators which might be trying to sneak up on them.

For predatory raptors such as barn owls, having forward-facing eyes helps them to see depth and distance much more clearly, since both eyes can focus on the same object at the same time. This is perfect for spotting and catching small prey such as field mice.

So though it might seem like birds with eyes on the side of their heads can’t see where they are going, they can see forward and sideways at the same time, and in fact can see much more than those with eyes facing forwards.

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to us. You can:

* Email your question to curiouskids@theconversation.com
* Tell us on Twitter by tagging @ConversationUK with the hashtag #curiouskids, or
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Please tell us your name, age and which town or city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question, but we will do our best.

More Curious Kids articles, written by academic experts:

• How does gravity pull things down to Earth? – Gabriel, age 4, Stewartby, UK

• What sea creature can attack and win over a blue whale? – Drake, age seven, Sydney, Australia

• What is fire? – Lyra, age seven, Oxford, UK

Hazel Jackson, Affiliate, University of Kent

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Curious Kids is a series for children of all ages, where The Conversation asks experts to answer questions from kids. All questions are welcome: find out how to enter at the bottom of this article.

People say that everything is made of molecules. Are feelings made of molecules? Is sound made of molecules? – Claire, age six, Bristol, UK

Thanks for the question, Claire. First things first: when people say “everything”, often they actually mean the stuff that scientists call “matter”. Matter is stuff you can touch. But feelings are not matter, and neither is sound.

Things that are matter include stars, air, water, tables, chairs, trees, your body, your brain, and pretty much everything that you see around you.

All of these things are made up of molecules – but molecules aren’t the smallest pieces of matter, because every molecule is made up of even smaller pieces called atoms.

And atoms themselves are made up of even tinier pieces. One of the tiniest types of pieces that makes up matter is called the electron.

Electrons and emotions

Things that are not matter include feelings, thoughts and light. Light allows us to see all of the things around us, but it’s different from matter. The main difference is that it doesn’t weigh anything. Even air has a weight, but light doesn’t.

Feelings and thoughts also don’t have a weight, and are not matter. But they’re not light, either. Feelings and thoughts live inside our brains.

The way that the matter in our brains acts affects our feelings and thoughts, and our feelings and thoughts can affect the way the matter in our brain acts.

Scientists don’t yet know exactly how thoughts are made, but they do know that it has something to do with the way those tiniest pieces of matter – electrons – move around to create an electrical signal, like the signals that are sent from a light switch to turn a light on.

For example, scientists have found out that your brain holds on to memories by keeping electrons in certain places.

There are different kinds of feelings. There are feelings that your body tells you, like when you burn your finger on a candle or when you feel hungry. And there are feelings that we call emotions, like when you’re sad or excited.

Both kinds of feelings are made in your brain and both kinds have to do with those electrons again, with how they move and where they sit in your brain.

Sensing sound

Sound is a different thing again. Sound is made of waves, but not really like waves on the ocean. Soundwaves are created when the molecules around us move in a certain way.

Imagine you’re playing some loud music through a speaker. If you touch the front of a speaker while the music’s playing, you should be able to feel it jiggle.

The jiggle of the speaker causes the molecules in the air around it to jiggle and bump into each other.

That little jiggle causes the other molecules nearby to jiggle, and the jiggles pass from one group of air molecules to another, until they finally reach the air molecules next to your ear drum.

Your ear drum is very sensitive, and can tell that the air molecules are jiggling, so it sends a special message to your brain. Your brain gets the message and says, “that’s music!” – and that’s how you hear the song.

So, neither feelings nor sound are made of molecules in the same way that matter is. But they both have a lot to do with the way molecules – and their smaller parts, atoms and electrons – move around.

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to us. You can:

* Email your question to curiouskids@theconversation.com
* Tell us on Twitter by tagging @ConversationUK with the hashtag #curiouskids, or
* Message us on Facebook.

Please tell us your name, age and which town or city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question, but we will do our best.

More Curious Kids articles, written by academic experts:

• Is it true dogs don’t like to travel? – Ankush, India

• How do eyes grow? – Annette, age seven, Stratford-upon-Avon, UK

• Who were the Spartans? – Trystan, a young reader from Australia

Laura Kormos, Senior Lecturer in Physics, Lancaster University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

In southeast Queensland, roughly 250 kilometres from Brisbane, lies the tiny town of Murgon. Located on Wakka Wakka Country, it’s home to about 2,000 people – and one of the most important fossil sites in the world.

From the 55 million-year-old clays there, palaeontologists have unearthed a range of precious fossils over several decades. These include the world’s oldest fossil songbirds, the only known fossils of salamanders in Australia and the oldest fossil marsupial remains in Australia.

And the site continues to serve up ancient treasures. In a new study, published today in the Journal of Vertebrate Paleontology, my colleagues and I report the discovery of the oldest crocodilian eggshells ever found in Australia.

These eggshells now serve as the basis for a new eggshell type, Wakkaoolithus godthelpi. They belong to the oldest known member of a now extinct group of crocodiles known as mekosuchines. And they offer a new look into not just their evolution – but also the forest-lined wetlands they lived in.

Tree-climbing crocodiles

Mekosuchines were Australia’s own unique, local branch of the crocodile family. They dominated inland waters of the continent 55 million years ago. They were part of the group of species that includes alligators, true crocodiles, gharials and caiman.

But they represent a much older branch than the saltwater and freshwater crocs found in Australia today. These modern species made their way to the continent much later, as it came into contact with southeast Asia about five million years ago.

In the 1980s, fossil finds began to take off at sites such as Murgon and the Riversleigh World Heritage Area in Queensland, and Alcoota in the Northern Territory. Since then, palaeontologists have been able to piece together a good picture of the diversity of mekosuchines. This was much higher than what we see today, with ten extinct genera now accounted for.

These fossil finds preserve a vigorous evolutionary history, and in particular a trend towards land-based hunting by about 33 million years ago.

This diversity includes the likes of Quinkana, a large land-based crocodile with narrow jaws, and dwarf species such as Trilophosuchus which may have been in a position to fill the niche of a tree-climbing hunter – a kind of “drop croc”.

The latter case was originally suggested by palaeontologist Paul Willis on the basis of the unusual musculature at the back of Trilophosuchus’s skull. Although hotly debated, Willis suggested this would allow Trilophosuchus to hold its head aloft and scan through the three dimensional environment of the canopy.

Reading eggshells

The new study, however, takes a look at one of the oldest genera of Mekosuchines, Kambara. It grew up to two metres long and is thought to have fed on fish and softshell turtles.

At Murgon, University of New South Wales researchers led by Henk Godthelp and Michael Archer uncovered fragments of eggshell, a comparatively rare find. Surprisingly little work has been done in the area of analysing crocodile eggshells.

Xavier Panadès I Blas from the Institut Català de Paleontologia at the University of Barcelona took up the challenge to explore the shell’s preserved microstructure with high-resolution microscopy.

What he found was intriguing. The eggshells of Kambara have their own unique micro-structural features, still preserved after 55 million years.

These features differ from what we know of the microstructures that have evolved among modern crocodiles and alligators. However, it will take a lot more work to put things formally into context.

Still, these eggshells may provide a valuable new avenue for understanding how mekosuchines fit into the big picture of evolution that spans Australia, Asia, Africa and the Americas.

A window into an ancient ecosystem

Beyond evolution, these eggshells are an insight into the environment that existed at Murgon 55 million years ago. Crocodile reproduction is intimately tied to their local environment and modern species display a complex mix of nesting strategies in response.

In the case of the eggshell of Kambara, there is little sign of degradation from bacteria.

This suggests the nest may have experienced periods of dryness due to the ephemeral nature of the surrounding wetlands at Murgon.

While mekosuchines enjoyed a much larger range of territories compared to our modern crocodiles, they eventually experienced a considerable contraction as the continent became increasingly arid.

Between this and the decline of large prey, mekosuchines eventually went extinct on the Australian continent.

Michael David Stein, Research Associate, School of Biological, Earth & Environmental Sciences, UNSW Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to curiouskidsus@theconversation.com.

Why do people have two sets of teeth? – Ivy D., age 11, Hyde Park, New York

Teeth help animals bite and chew food. Meat-eating carnivores tend to have sharp teeth to sink into their prey, while herbivores tend to have flatter teeth to grind down their plant-based meals.

Some animals also use their pearly whites for specialized purposes like digging or fighting. Tusks, like you see in elephants, walruses and warthogs, are one special kind of teeth – they grow continuously for as long as the animal is alive.

Over time, no matter what you use them for, teeth wear down. This is good news if you’re a rodent, such as a beaver or a rat. Because their teeth never stop growing, rodents rely on gnawing and chomping to grind their teeth down so they don’t grow so long that they cause problems.

Some animals deal with wear and tear by continuously developing new teeth as their old ones fall out. Sharks and crocodiles, for example, are what scientists call polyphyodont: They can grow nearly infinite sets of teeth.

Like most mammals, humans are diphyodont: We have two sets of teeth – baby teeth and adult teeth. The technical term for our baby teeth is deciduous teeth because they fall out, the same way deciduous leaves fall off trees in autumn.

We are a dentist who focuses on treating kids and an anthropologist who studies how humans’ teeth and faces grow. We are both passionate about teeth and oral health care, and love thinking and learning about teeth. How did two sets become standard for human beings?

How human teeth develop

Most people are born with no teeth showing in their mouths at all, even though your baby teeth start developing before you’re even born. Baby teeth usually start poking through the gums when you’re between 6 and 8 months old. Sometimes when dentists take X-rays to check for cavities or other problems, they can see adult teeth growing within the gums.

Baby teeth are relatively small because they need to fit in the small faces of babies and little kids. As you grow older and your face gets bigger, you have room in your mouth for more and larger teeth. Teeth have different sizes and shapes, depending on their purpose. Human front teeth are good at biting into things and tearing off a piece of food. Your back teeth are good at chewing foods into smaller bits before you swallow.

Most kids lose their first baby tooth when they’re between 5 and 6 years old, and the process slowly continues until you’re between 10 and 12 years old and all 20 of your original choppers have fallen out.

During that same time, your adult, or permanent, teeth gradually take their spots in your mouth. They’re bigger than your baby teeth and can help you chew more food at once. Eventually you have a set of 28, with the potential of four more wisdom teeth at the very back. Some people just naturally don’t ever grow wisdom teeth, some have wisdom teeth that don’t fit their jaws and need to be removed, and some have big, wide smiles with 32 teeth.

So, getting two sets of teeth means your teeth fit the size of your face as you grow, and helps make sure you can chew food your entire life.

Baby teeth deserve gentle care

You might be thinking that if baby teeth are just going to fall out, they can’t be that important. But that’s not true.

If you were a shark, every time you got a bunch of cavities or chipped a tooth, you’d just grow a new one and keep on chewing. But unlike sharks or crocodiles or even manatees, we humans only get two sets of teeth. By taking care of your baby teeth, you can keep them healthy and make sure they stay right where they belong until they’re ready to fall out.

If you don’t take care of your baby teeth, they can wind up with lots of cavities. If the cavities get too large or teeth become infected, they may need to be removed by the dentist. Not only is this process not fun, but taking out baby teeth too early can create problems for your adult teeth.

You can wind up with not enough space for your adult teeth to come in – that is, what dentists call “erupt” – into the right spots. This issue happens in part because the other teeth around where the baby tooth was will shift and may move into the space where your adult teeth are supposed to come in. Teeth can get stuck in the jaw and not erupt, or your teeth can be crowded in your mouth. If there is a mismatch between the size of your teeth and the size of your jaws, an orthodontist might attach braces to your teeth to reposition them so they all fit.

What is the future of teeth?

Because people can live long lives, 70 or 80 years or more, many outlive their teeth even if they do their best to take care of them. While there are lots of options for artificial teeth – like removable dentures or even dental implants, which are fake teeth that are screwed into your jaws – it’s not quite the same as having natural teeth.

If you break a bone, it heals because you can grow new bone to patch up the part that broke. Scientists call this process fracture healing. Human teeth aren’t bone and, unfortunately, do not heal themselves. Unlike your bones, which are mostly composed of a structural protein your body makes called collagen, your teeth are primarily made up of minerals such as calcium-rich hydroxyapatite. In some ways, teeth are closer to being like hard stones than living bones.

Regenerative dentistry is the study of how teeth grow and develop, with the goal of ultimately designing new ways to repair and replace our teeth. Scientists are working hard to figure out ways to grow new teeth or help existing teeth regenerate. They’re learning about the environment and materials needed to grow new teeth.

For now, the best thing you can do is take good care of the teeth you have and keep the gums and bones that support them healthy. Brush your teeth twice a day with toothpaste that contains fluoride, and floss once a day. Try to limit sugary, sticky foods and drinks – a good diet keeps your whole body healthy, not just your teeth. See a dentist regularly, and protect your teeth from injury.

Being kind to your teeth now can help your future self have a beautiful, healthy smile.

Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the city where you live.

And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.

Christina Nicholas, Associate Professor of Orthodontics and of Anthropology, University of Illinois Chicago and David Avenetti, Associate Professor of Pediatric Dentistry, University of Illinois Chicago

This article is republished from The Conversation under a Creative Commons license. Read the original article.