When I (Nathan Brooks English) was six years old, I snuck a starfish home from the beach and hid it in my closet. I regret that now, as my parents did then when the smell of rotting starfish overwhelmed the house. I regret it also because that starfish had a place and a purpose – and dying in a hot, dark closet next to my Hot Wheels was not it.

Likewise, the beautiful shells and natural flotsam that decorate Australian beaches have a place and a purpose. For many of us, summer at the beach is a cherished memory and collecting seashells is probably a part of that memory.

On most beaches in Australia, collecting shells without living creatures in them is legal, but let me convince you there are better options that ensure future Sallies will still find seashells by the seashore.

Someone needs that shell more than you

For native wildlife, both occupied and unoccupied shells provide important shelter and sources of calcium and grit.

Taking that beautiful snail shell could increase the cost of housing for a hermit crab or the small shrimp that needs it next. The beautiful conch shell that calls to you is actually an octopus caravan.

For these reasons, never pick up shells in the water or in tidal pools; chances are they are being used or will be shortly.

Likewise, collecting shells in marine parks is strictly prohibited.

Shells have spiritual and cultural importance

For the island Woppaburra People of central Queensland, beaches and shells have spiritual and cultural importance as part of Dreaming stories, dance and ceremonies.

In addition to their place and purpose in my (Robert Muir) stories and culture, shells can also provide valuable insight and context to our history on the island.

Middens (deep piles of shells left on the beach after being used to produce food or tools) provide archaeological evidence that the islands have been occupied for at least the past 5,000 years.

Back then, Woppa (also known as Great Keppel Island, in Queensland) and its beaches could sustainably support the 100 to 200 people who lived on the island for more than five millenia.

Today, Woppa hosts tens of thousands of visitors a year on three small beaches. And while people are welcome to pick up, examine and play with the shells, to preserve their place and purpose they must be left on the shore where they were found.

If everyone took a shell…

Increasing pressure on beaches and their natural resources isn’t just felt on Woppa.

The global population now exceeds 8 billion people and our collective (pun intended) impact on beaches is magnified. That’s twice as many people as when I (Nathan Brooks English) was a child in the late 1970s.

For example, in 2019 Bondi Beach had more than 2.1 million visitors (not that anyone is looking at shells). If everyone took a shell, there’d be hardly any left.

Even smaller beaches need time to accumulate shells and a summer rush of collectors can quickly deplete beaches of shells until the next cyclone or winter storm washes more up.

What to do instead of collecting shells

So how do we balance wanting a tangible reminder of the beach in our own yards or homes (the destination of many shells) versus not damaging the natural beauty and function of beach ecosystems?

Instead of taking a shell, take a picture instead. You can photograph unoccupied shells in place along the beach where the tide has collected, or arrange them together for a photographic collage.

Include them in your sandcastles as gates, windows, or little people to populate the castle.

For your artsy children (or adults), use crayons or coloured pencils and a small sketch pad to draw the shells.

Taking a few shells at a time to your umbrella to sketch them and then returning them to the tide line will sate the urge to collect and leave the beach unchanged.

You may even find you have a gifted scientific illustrator on your hands.

When you’re done with the shells, leave them by the shore. Wind, tides and time (or tomorrow’s small visitor) will sweep them back into natural circulation, continuing their storied lives as creature homes or fine grit for our beautiful Australian beaches, their purpose and place preserved.

If you absolutely must pick something up and take it home, please pick up some of the vast amount of plastic found on Australian beaches.

Nathan Brooks English, Associate professor; Flora, Fauna & Freshwater Research Cluster Lead, CQUniversity Australia and Robert Muir, Project Officer at the Woppaburra TUMRA Aboriginal Corporation, Indigenous Knowledge

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

Curious Kids is a series for children. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.

My name is Abhilasa. I am 10 years old and I live in Melbourne. My question is: Why are people colour blind? – Abhilasa, age 10, Melbourne.

Hi Abhilasa. Thank you for your great question.

Let’s say you have three tubs of paint: blue, green and red. You have a paintbrush and a piece of paper. You can use the three paints to make lots of different things. A green tree, a blue car, or a red apple. And if you want to paint a purple shirt, you can mix red and blue paint to make purple.

How do we see those different colours? In your eye you have special kinds of cells that pick up the light rays bouncing off each splotch of paint. These cells are called cone cells.

In the microscope, they look like ice-cream cones. But they are much smaller. The cone cells help you see the different colours.

There are three kinds of cone cell in most people’s eyes. They are called long wave cones, medium wave cones, and short wave cones, because they pick up different kinds of light waves (or rays).

The cone cells tell the brain how much of each type of light wave is bouncing off each splotch of paint.

Your brain puts those messages back together again.

So let’s say you mix red and blue paint to make a purple splotch. Lots of long and short wave light will bounce off that splotch, but not much medium wave light will (the reason this happens is hard to explain, but you just have to trust me that this is how light works). Then the long and short cones in your eyes get activated, and will send their message to the brain. The brain interprets the message and voilà! The splotch will look purple to you.

Colour blind people can still can see colours, but not as many as most people do. That’s because the cone cells in their eyes may be different.

Some colour blind people only have two kinds of cone cell in their eye. Others have three kinds, but the cones do not pick up the same light waves as the cone cells in most people’s eyes do. So their brain does not get three different messages like most people’s brains do.

Being colour blind is a bit like what would happen if I took away one of your tubs of paint, so you only have two tubs. You could still make some different-coloured splotches, but not as many as when you had three tubs. That would not be so much fun. Being colour blind is sometimes not much fun either. Some kids laugh in school when colour blind kids get their coloured pencils mixed up. That’s mean.

But being colour blind can be good, too. Colour blind people are really good at spotting things that are far away, and they are better than most people at telling things apart by their shape.

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

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Please tell us your name, age and which 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.

Paul Martin, Professor of Clinical Ophthalmology & Eye Health, Central Clinical School, Save Sight Institute, University of Sydney

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

As a kid, it was tough for me to grasp the massive time scale of Earth’s history. Now, with nearly two decades of experience as a geologist, I think one of the best ways to understand our planet’s history and evolution is by condensing the entire timeline into a single calendar year.

It’s not a new concept, but it’s a powerful one.

So, how do we go about this? If we consider Earth’s age as 4.54 billion years and divide it by 365 days, each day of the Gregorian calendar represents about 12.438 million years.

Let’s say we want to calculate what “day” the Paleozoic started in our new Earth calendar. We just need to subtract 541 million years from the age of the planet and divide it by 12.438 million years. Simple, right?

As I ran these equations, I noticed something amusing. Some of the most significant events in Earth’s history coincide with major holidays in the Western world. By this reckoning, the dinosaurs went extinct on Christmas Day.

The Earth calendar

View the events in the infographic above, or scroll down to read about the entire year in order.

January 1

4.54 billion years ago: Formation of proto-Earth as part of the Solar System

Dust and gas in the early Solar System collide and combine under gravity. This process eventually leads to the formation of a molten planet, our proto-Earth.

January 3

4.5 billion years ago: Theia’s impact and the formation of the Moon

A Mars-sized planet, Theia, collides with the proto-Earth, changing the composition of our planet forever. This massive impact ejects a significant amount of material into orbit around Earth, which eventually coalesces to form the Moon.

February 4

4.1 billion years ago: Beginning of the Late Heavy Bombardment

Earth, the Moon and other inner bodies of our Solar System experience intense asteroid and comet impacts, which shape their surfaces. Unlike Earth, the Moon still retains these craters today because it lacks an atmosphere, water and tectonic activity. The bombardment continues until the very end of February – 3.8 billion years ago.

February 14

3.97 billion years ago: Beginning of the Archean Eon

By Valentine’s Day, the hottest period in Earth’s history – the Hadean Eon – has finally come to an end. With these hostile conditions in the past, the stage is lovingly set for life to emerge as the Archean Eon begins.

March 16

3.6 billion years ago: Formation of the first supercontinent, maybe

For a couple of weeks now, Earth has been cool enough to form stable continental crusts. Vaalbara is a theorised supercontinent consisting of two cratons (ancient, stable and thick blocks that form the cores of continents): Kaapvaal in eastern South Africa, and Pilbara in north-western Western Australia. While still under debate, this would make Vaalbara 3.6 to 2.7 billion years old, one of the oldest supercontinents we know of.

March 26

3.48 billion years ago: Earliest direct evidence of life

Right before the end of the first quarter of the year, simple prokaryotic organisms appear during the Paleoarchean. These are the earliest direct evidence of life recorded as microfossils (stromatolites).

May 27

2.7 billion years ago: Cyanobacteria become the first oxygen producers

Blue-green algae called cyanobacteria develop oxygenic photosynthesis. They use sunlight to convert carbon dioxide and water into organic compounds, releasing oxygen as a byproduct. It’s a milestone for the development of our current atmosphere.

June 16

2.46 billion years ago: The Great Oxygenation Event

A dramatic rise in oxygen levels occurs in shallow seas and in Earth’s atmosphere, driven by oxygenic photosynthesis from cyanobacteria. This event lasts approximately 400 million years, transforming Earth’s environment and paving the way for more complex life forms to thrive on a radically changed planet.

September 17

1.3 billion years ago: Formation of the supercontinent Rodinia

One of the first supercontinents to form on Earth, Rodinia brings together most of the planet’s landmasses. During its 550 million years of existence, Earth is predominantly inhabited by simple life forms, including prokaryotes and early eukaryotes.

October 31

750 million years ago: Breakdown of Rodinia and Snowball Earth events

By Halloween, Rodinia begins to crack apart just like candies in a kid’s trick-or-treat bag. The breakup of Rodinia dramatically influences the planet’s climate and ocean circulation, potentially triggering Snowball Earth events. These two major global glaciations, lasting approximately 70 million years, play a significant role in shaping Earth’s history.

November 9

635 million years ago: The Ediacaran Period begins

Right before the start of the Paleozoic, the first large, complex, multi-cellular marine life forms appear. The Ediacaran biota includes diverse, soft-bodied organisms – early animals, algae and other complex life. Today, curious visitors to the Flinders Ranges in South Australia might be lucky enough to spot some Ediacaran fossils.

November 17

538.8 million years ago: The Cambrian Explosion

The Cambrian Explosion lasts no more than two days (25 million years). During this time, sudden development of complex life occurs in the oceans. Almost all present-day animal phyla appear, and other groups diversify in major ways. Undoubtedly, this is a critical period for life on our planet.

November 23

470 million years ago: Plants first colonise Gondwanaland during the Ordovician Period

Early land plants are simple, non-vascular organisms that colonise moist environments – much like moss today. Over time, plants evolve more complex structures, including vascular tissue specialised for transporting water, nutrients and food, allowing them to thrive in a wider range of terrestrial habitats.

December 1

370 million years ago: First vertebrates move onto land

On the very first day of December, four-limbed animals called tetrapods are the first animals with backbones (vertebrates) to transition to a life on land during the Late Devonian period. These are the ancestors of all land-dwelling vertebrates, living and extinct.

December 10

252 million years ago: Permian-Triassic mass extinction

Life is almost entirely obliterated after a series of massive Siberian volcanic eruptions trigger global warming and a lack of oxygen in the oceans. The Great Dying is the largest extinction in Earth’s history, wiping out more than 90% of marine species and about 70% of terrestrial species.

December 12

230 million years ago: The rise of dinosaurs

The very first dinosaurs are small, bipedal reptiles that eventually evolve into the diverse group of animals that dominate Earth during the Mesozoic Era. Dinosaurs reign over our planet for 13 days, meaning their kingdom endures for an epic 165 million years.

December 25

66 million years ago: Cretaceous-Paleogene mass extinction

Christmas Day is not a joyful day for dinosaurs: they go extinct. The current leading hypothesis for their demise is an asteroid impact in the Yucatán Peninsula of Mexico. A massive space lump of coal from Santa, if you will.

December 26

56 million years ago: The rise of mammals

Boxing Day is a good day for mammals. During the Palaeocene, right after the extinction event, mammals begin to grow in size and diversity. By noon, when the Eocene starts 56 million years ago, they have evolved into the first large herbivores and carnivores.

December 31: midday

~7 to 6 million years ago: The planet of the apes

The very first hominids, either Sahelanthropus or Orrorin, appear by noon on December 31. These species represent some of the earliest common ancestors of humans and other great apes, such as gorillas, orangutans and chimpanzees.

December 31: 11:25pm

300,000 years ago: Modern humans finally arrive

The very first Homo sapiens emerge in Africa, marking the beginning of anatomically modern humans.

The final ten minutes

We’re almost at midnight, and nearly all of humanity’s history can be condensed into the last ten minutes of the year.

11:50pm

~86,377 years ago: Homo sapiens migrate out of Africa into Eurasia. Thus begins a significant global colonisation by early modern humans.

11:51pm

~77,740 years ago: The first symbolic art. Engraved ochre in South Africa’s Blombos Cave is considered one of the earliest symbolic artworks created by humans, indicating the development of cognitive and cultural sophistication.

11:52pm

~69,102 years ago: The Last Glacial Period. An ongoing global cooling event intensifies, forcing humans to adapt to harsher climates.

11:53pm

~60,464 years ago: Humans reach Australia. This marks the earliest known migration across sea, and settlement on a new isolated continent.

11:54pm

~51,826 years ago: Upper Paleolithic Revolution. Humans arrive at a capacity for well-developed language, more complex social structures, and highly specialised tools.

11:55pm

~43,119 years ago: The Neanderthals go extinct. Multiple factors cause their demise, including violence, diseases, natural catastrophes and being outcompeted by Homo sapiens, the only remaining hominid species on Earth.

11:56pm

~34,551 years ago: Symbolic art flourishes and culture emerges globally among modern humans. This time is characterised by significant advancements in creativity and social organisation.

11:57pm

~25,913 years ago: The Last Glacial Maximum. Ice sheets reach their greatest extent, covering large parts of North America, Europe and Asia. This is the peak of the most recent ice age, affecting both ecosystems and human migration.

11:58pm

~17,275 years ago: Warming begins after the Last Glacial Maximum. Ice sheets gradually retreat, leading towards the end of the last ice age.

11:59pm

~8,638 years ago: Significant events take place globally. The Agricultural Revolution has started, with humans cultivating crops and domesticating animals, leading to the first permanent settlements and village life.

Midnight

8,638 years ago to today: A great deal happens in the last few seconds of the year. From the Bronze and Iron Age, to the rise and fall of major empires, the Renaissance, the Industrial Revolution, world wars, space exploration, the internet and artificial intelligence.

Francisco Jose Testa, Lecturer in Earth Sciences (Mineralogy, Petrology & Geochemistry), University of Tasmania

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 does a rocket have to go 25,000 mph (about 40,000 kilometers per hour) to escape Earth? – Bo H., age 10, Durham, New Hampshire

There’s a reason why a rocket has to go so fast to escape Earth. It’s about gravity – something all of us experience every moment of every day.

Gravity is the force that pulls you toward the ground. And that’s a good thing. Gravity keeps you on Earth; otherwise, you would float away into space.

But gravity also makes it difficult to leave Earth if you’re a rocket heading for space. Escaping our planet’s gravitational pull is hard – not only is gravity strong, but it also extends far away from Earth.

Like a balloon

As a rocket scientist, one of the things I do is teach students how rockets overcome gravity. Here’s how it works:

Essentially, the rocket has to make thrust – that is, create force – by burning propellant to make hot gases. Then it shoots those hot gases out of a nozzle. It’s sort of like blowing up a balloon, letting go of it and watching it fly away as the air rushes out.

More specifically, the rocket propellant consists of both fuel and oxidizer. The fuel is typically something flammable, usually hydrogen, methane or kerosene. The oxidizer is usually liquid oxygen, which reacts with the fuel and allows it to burn.

When going into space and escaping from Earth, rockets need lots of force, so they consume propellant very quickly. That’s a problem, because the rocket can’t carry enough propellant to keep thrusting forever; the amount of propellant needed would make the rocket too heavy to get off the ground.

So what happens when the propellant runs out? The thrust stops, and gravity slows the rocket down until it gradually begins to fall back to Earth.

Fortunately, scientists can launch the rocket with some sideways momentum so that it misses the Earth when it returns. They can even do this so it continuously falls around the Earth forever. In other words, it goes into orbit, and begins to circle the planet.

Many launches intentionally don’t completely leave Earth behind. Thousands of satellites are orbiting our planet right now, and they help phones and TVs work, display weather patterns for meteorologists, and even let you use a credit card to pay for things at the store or gas at the pump. You can sometimes see these satellites in the night sky, including the International Space Station.

Escaping Earth

But suppose the goal is to let the rocket escape from Earth’s gravity forever so it can fly off into the depths of space. That’s when scientists do a neat trick called staging. They launch with a big rocket, and then, once in space, discard it to use a smaller rocket. That way, the journey can continue without the weight of the bigger rocket, and less propellant is needed.

But even staging is not enough; eventually the rocket will run out of propellant. But if the rocket goes fast enough, it can run out of propellant and still continue to coast away from Earth forever, without gravity pulling it back. It’s like riding a bike: build up enough speed and eventually you can coast up a hill without pedaling.

And just like there’s a minimum speed required to coast the bike, there’s a minimum speed a rocket needs to coast away into space: 25,020 mph (about 40,000 kilometers per hour).

Scientists call that speed the escape velocity. A rocket needs to go that fast so that the momentum propelling it away from Earth is stronger than the force of gravity pulling it back. Any slower, and you’ll go into an orbit of Earth.

Escaping Jupiter

Bigger, or more massive, objects have stronger gravitational pull. A rocket launching from a planet bigger than Earth would need to achieve a higher escape speed.

For example, Jupiter is the most massive planet in our solar system. It’s so big, it could swallow 1,000 Earths. So it requires a very high escape speed: 133,100 mph (about 214,000 kilometers per hour), more than five times the escape speed of Earth.

But the extreme example is a black hole, an object so massive that its escape speed is extraordinarily high. So high, in fact, that even light – which has a speed of about 670 million mph (over a billion kilometers per hour) – is not fast enough to escape. That’s why it’s called a black hole.

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.

This article has been updated to correct the speed of light.

Benjamin L. Emerson, Principal Research Engineer, School of Aerospace Engineering, Georgia Institute of Technology

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

Curious Kids is a series for children. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.

I would like to know how long garden snails would live if they were not eaten by birds (or other predators)? – Alice, age 6, Canberra.

That’s a really good question! There have been reports of at least one snail living as many as 14 years in captivity. His name was George and he lived in Hawaii, in the United States.

Very few people have ever had the patience to study how long garden snails live in the wild. However, it might be longer than we might at first think – studies showed that snails in gardens in California needed to be between two and four years old before they were old enough to have babies. Many of these Californian garden snails, which were studied for almost five years, were therefore over six years old at least – older than you, Alice! It seems that rats and small mammals were the main predators of these snails.

Counting snail shell rings

There is a snail very like the garden snail that is called the Roman or Apple snail – it is the one that some people like to eat.

A study of a population of these snails in England was able to work out how old these snails are. That’s because, as they get older, you can count growth rings at the edge of their shell.

Some of the snails were at least six years old and probably more like eight or nine. The older snails had very thick shells and were often out and about. The scientists thought this might be because as the snails got older and bigger, fewer birds and other predators could crack their thick shells, and so they felt safe enough not hide away all the time.

So, it seems that if you are a snail that can survive long enough to get big then you might stand a good chance of getting even older – maybe 15 years old. It depends on what type of snail you are.

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au

Please tell us your name, age and which city you live in. We won’t be able to answer every question but we will do our best.

Bill Bateman, Associate professor, Curtin University

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