.

  • Written by Alan Collins, Professor of Geology, University of Adelaide
Rocks contain a layer-by-layer record of the history of our planet. Fred Moore/flickr, CC BY-NC

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.


Where do rocks come from? - Claire, age 5, Perth, WA.

Wow, Claire, what a great question. Sitting in a university, I rarely get asked such brilliant questions. So, thank you.

As strange as it sounds, rocks are made from stardust; dust blasted out and made from exploding stars.

In fact, our corner of space has many rocks floating around in it. From really fine dust, to pebbles, boulders and house-sized rocks that can burn up in the night sky to make meteors or “shooting stars”.

The Moon and our local planets – Mars, Venus and Mercury – are just the largest rocks floating around our part of space. These are all made from space dust stuck together over billions of years.


Read more: Curious Kids: how was the Earth made?


An artist’s impression of early Earth, which was then a molten ball of lava flying through space. NASA/JPL-Caltech, CC BY

The ‘light’ rocks are on the Earth’s surface

Planet Earth is a rock too, but so much has happened since it was formed from dust and small rocks that smashed and stuck together 4.543 billion years ago.

As the space dust hit each other to make the earth, it got super hot and melted. The Earth was, at that time, a spinning ball of red-hot lava flying through space.

In this melted lava planet, heavy bits of the earth sank and the light frothy bits gathered on the surface.

Have you ever looked closely at a glass of milky coffee at a cafe? The dark heavy coffee is at the bottom, whereas the light, frothy milk sits on the top. Well, our planet was a bit like that coffee billions of years ago.

We don’t see the really heavy rocks these days because they sank deep in the planet very early on. The rocks we see on the surface are like the frothy milk! They were light and rose to the top. Then, as time moved on, the planet cooled and froze to become the solid earth we have now.

I know most rocks are heavy. But in fact some rocks – even really big ones like Uluru – are actually much lighter than the rocks found in the deep Earth.

Lava and plates

Those rocks on the Earth’s surface actually move around. Large chunks the size of continents (called “plates”) jostle each other and this can cause earthquakes. Some of them get forced under other plates and heat up and eventually melt. This forms more lava. The lava erupts from volcanoes, then cools and forms new rocks.

Here are some pictures of lava in the melted state and then after it has cooled down:

Volcanic lava in Etra Ale Volcano in Ethiopia in 2016. Lava emerges from volcanoes and then cools on the Earth’s surface to form rocks. Petr Meissner/flickr, CC BY

Read more: Curious Kids: how do mountains form?


Mountains and gems are also rocks

Mountains form where two plates smash into each other. The rocks that get caught between two of the Earth’s plates get squashed under huge pressures and heat up. These can form really beautiful rocks. Sometimes gems form in these rocks and people try to find them to make jewellery.

Rain and ice break up the rocks in mountains. These form sand and mud that get washed out to form beaches, rivers and swamps. This sand and mud can get buried, squashed and heated, which eventually turns them into rocks.

Rocks contain a record of the history of our planet; what is has been through and what is capable of. We are only just learning how to read it.

So, next time you see a rock, just think what an incredible story it contains.

Spectacular layered sedimentary rocks from Tigray, Ethiopia, where each layer represents an ancient sea bed. Rocks of these types contain the history of the surface of the planet. Author provided

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

CC BY-ND

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.

Alan Collins receives funding from a number of industry and government sources including the Australian Research Council

Authors: Alan Collins, Professor of Geology, University of Adelaide

Read more http://theconversation.com/curious-kids-where-do-rocks-come-from-116429

An 8-year-old made US$22 million on YouTube, but most social media influencers are like unpaid interns

A whopping 12% of the population aged 13 to 38 consider themselves social influencers, according to marketing company Morning Consult. www.shutterstock.comLike any eight-year-old, Ryan Kaji loves to p...

Dr Natalya Saldanha, Academic, RMIT University - avatar Dr Natalya Saldanha, Academic, RMIT University

Domestic violence will spike in the bushfire aftermath, and governments can no longer ignore it

Over the past two weeks, bushfires have raged across New South Wales and Queensland. While the narrative appears focused on potential causes and political point-scoring, what’s lost in this disc...

Rowena Maguire, Senior Lecturer, Faculty of Law, Institute for Future Environments, Queensland University of Technology - avatar Rowena Maguire, Senior Lecturer, Faculty of Law, Institute for Future Environments, Queensland University of Technology

The main problem with virtual reality? It's almost as humdrum as real life

Virtual horse racing, at a real racecourse? Zero points for imagination. Rachel Grey/AAP ImageJust a few years ago, virtual reality (VR) was being showered with very real money. The industry raised an...

Tomas Trescak, Senior Lecturer in Intelligent Systems, Western Sydney University - avatar Tomas Trescak, Senior Lecturer in Intelligent Systems, Western Sydney University

Children learn through play – it shouldn’t stop at preschool

Over the next few weeks, many preschoolers will meet their foundation teachers, spend some time in a classroom and hopefully make some new friends. from shutterstock.comThe transition from preschool t...

Kate Noble, Education Policy Fellow, Mitchell Institute, Victoria University - avatar Kate Noble, Education Policy Fellow, Mitchell Institute, Victoria University

GOD save us: greenspace-oriented development could make higher density attractive

The lure of suburbia clearly remains strong. To deal with sprawl, planners need to increase urban density in a way that resonates with the leafy green qualities of suburbia that residents value. Juli...

Julian Bolleter, Deputy Director, Australian Urban Design Research Centre, University of Western Australia - avatar Julian Bolleter, Deputy Director, Australian Urban Design Research Centre, University of Western Australia

Re-imagining a museum of our First Nations

The Quandamooka Art, Museum and Performance Institute offers a new way of considering the shape of First Nations museums in Australia. Cox Architecture/QYACIndigenous voices are finally being ackno...

Kieran Wong, Adjunct Senior Research Fellow, Monash University - avatar Kieran Wong, Adjunct Senior Research Fellow, Monash University

Making sense of menopausal hormone therapy means understanding the benefits as well as the risks

Grappling with the pros and cons of menopausal hormone therapy can be confusing. From shutterstock.comAt menopause, a woman’s ovaries lose their reproductive function. Eggs are no longer release...

Susan Davis, Chair of Women's Health, Monash University - avatar Susan Davis, Chair of Women's Health, Monash University

What are the best bed sheets

Looking for new bedsheets? With so much choice on the market, finding the best bed sheets can be a challenge – but when you’re between the sheets for so many hours, it’s important to get it ri...

Digital 360 - avatar Digital 360

6 Groovy ‘70s Costume Ideas to Help You Stand Out at Your Next Retro Party

In the early 1970’s Vogue magazine famously proclaimed, “There are no rules in the fashion game now.” Indeed, by following in the footsteps of the ‘60s – defying old traditions and exp...

Digital 360 - avatar Digital 360

Chinese embassy says Liberal critics Hastie and Paterson should “repent”

The Chinese embassy has lashed out at two Liberal members of parliament, Andrew Hastie and James Paterson, saying they would need to “repent and redress their mistakes” before they would b...

Michelle Grattan, Professorial Fellow, University of Canberra - avatar Michelle Grattan, Professorial Fellow, University of Canberra

VIDEO: Michelle Grattan on the government's response to the bushfires

University of Canberra Deputy Vice-Chancellor Professor Geoff Crisp discusses the the week in politics the government’s response to the bush fires as well as the Emergency Leaders for Climate Ac...

Michelle Grattan, Professorial Fellow, University of Canberra - avatar Michelle Grattan, Professorial Fellow, University of Canberra

Conditions built into Frydenberg's okay for Chinese baby formula takeover

Bellamy’s will have to have to manufacture in Victoria and keep its Australian headquarters for ten years. Bellamy’s AustraliaThe proposed acquisition of infant formula producer Bellamy&rs...

Michelle Grattan, Professorial Fellow, University of Canberra - avatar Michelle Grattan, Professorial Fellow, University of Canberra

Outdoor Lighting Solutions – How to Make the Right Choice?

Whether it’s your patio, your deck, your porch, or your backyard – your outdoor space needs to be illuminated properly if you want your entire property to look good. This is also a way to boos...

Diana Smith - avatar Diana Smith

Climate change: why Sweden's central bank dumped Australian bonds

Sweden's central bank ways it will no longer invest in assets from governments with large climate footprints, even if the yields were high. ShutterstockWhat’s happening? Suddenly, at the level...

John Hawkins, Assistant professor, University of Canberra - avatar John Hawkins, Assistant professor, University of Canberra

The Conversation Yearbook 2019: celebrate with us and grab your discounted copy

The Conversation's Deputy Health Editor, Phoebe Roth, and Assistant Editor: Technology, Noor Gillani, agree this is the must-have read of 2019. Wes Mountain/The ConversationA little bit of authority ...

Molly Glassey, Digital Editor, The Conversation - avatar Molly Glassey, Digital Editor, The Conversation

Place your bets: will banning illegal offshore sites really help kick our gambling habit?

While total gambling spending in Australia decreased during 2016-17, sports betting increased by 15.3%, from A$921 million to A$1.062 billion. SHUTTERSTOCKThe Australian Communications and Media Auth...

Charles Livingstone, Associate Professor, School of Public Health and Preventive Medicine, Monash University - avatar Charles Livingstone, Associate Professor, School of Public Health and Preventive Medicine, Monash University

Stop the world, I want to get off! In Exit Strategies, one woman leaves and leaves again

The script for Exit Strategies was developed by performer Mish Grigor during an artist’s residency in the UK, against the backdrop of Brexit. Bryony JacksonTo perform an exit is not as simple as...

Sandra D'urso, Researcher, The Australian Centre, University of Melbourne - avatar Sandra D'urso, Researcher, The Australian Centre, University of Melbourne

Sri Lanka election: will the country see a return to strongman politics?

Gotabaya Rajapaksa, the frontrunner in Sri Lanka's presidential election, faces a lawsuit in the US for alleged extrajudicial killing and torture. M.A. Pushpa Kumara/EPASri Lanka’s presidential ...

Niro Kandasamy, Tutor, University of Melbourne - avatar Niro Kandasamy, Tutor, University of Melbourne

Is social media damaging to children and teens? We asked five experts

They need to have it to fit in, but social media is probably doing teens more harm than good. from www.shutterstock.comIf you have kids, chances are you’ve worried about their presence on socia...

Alexandra Hansen, Chief of Staff, The Conversation - avatar Alexandra Hansen, Chief of Staff, The Conversation

Sick and Tired of Your Dead End Job? Try Teaching!

Tired of the same old grind at the office? Want an opportunity to impact lives both in your community and around the world? Do you love to travel and have new experiences? Teaching English is the perfect job for you! All you need is a willingness to ...

News Company - avatar News Company

The Impact of an Aging Population in Australia

There’s an issue on the horizon that Australia needs to prepare for. The portion of elderly citizens that make up the country’s overall population is increasing, and we might not have the infrastructure in place to support this. Australians h...

News Company - avatar News Company

LifeStyle

How to Make Your Girlfriend’s Birthday Extra Special

Your girlfriend’s birthday is your opportunity to show her how much you care. But how exactly do...

A Guide to Building Your Kid’s Confidence

As your child grows, confidence is key. Having low self-esteem as a child can have a detrimental e...

3 Hacks that Will Extend the Life of Your Hair Extensions

Everybody has the right to enjoy beautiful, long hair, including you! If you’ve always heard a...

Lessons in Empathy for Children

The ability to be able to understand and share the feelings of a fellow human being – empathy ...