The Times Australia
The Times World News

.

What created the continents? New evidence points to giant asteroids

  • Written by Tim Johnson, Associate Professor, Curtin University
What created the continents? New evidence points to giant asteroids

Earth is the only planet we know of with continents[1], the giant landmasses that provide homes to humankind and most of Earth’s biomass[2].

However, we still don’t have firm answers to some basic questions about continents: how did they come to be, and why did they form where they did?

One theory is that they were formed by giant meteorites crashing into Earth’s crust long ago. This idea[3] has been proposed several times[4], but until now there has been little evidence to support it.

In new research published in Nature[5], we studied ancient minerals from Western Australia and found tantalising clues suggesting the giant impact hypothesis might be right.

How do you make a continent?

The continents form part of the lithosphere, the rigid rocky outer shell of Earth made up of ocean floors and the continents, of which the uppermost layer is the crust.

The crust beneath the oceans is thin and made of dark, dense basaltic rock which contains only a little silica. By contrast, the continental crust is thick and mostly consists of granite, a less dense, pale-coloured, silica-rich rock that makes the continents “float”.

The internal structure of Earth. Kelvin Song / Wikimedia, CC BY[6][7]

Beneath the lithosphere sits a thick, slowly flowing mass of almost-molten rock, which sits near the top of the mantle, the layer of Earth between the crust and the core.

If part of the lithosphere is removed, the mantle beneath it will melt as the pressure from above is released. And impacts from giant meteorites – rocks from space tens or hundreds of kilometres across – are an extremely efficient way of doing exactly that!

What are the consequences of a giant impact?

Giant impacts blast out huge volumes of material almost instantaneously. Rocks near the surface will melt for hundreds of kilometres or more around the impact site. The impact also releases pressure on the mantle below, causing it to melt and produce a “blob-like” mass of thick basaltic crust.

This mass is called an oceanic plateau, similar to that beneath present-day Hawaii or Iceland. The process is a bit like what happens if you are hit hard on the head by a golf ball or pebble – the resulting bump or “egg” is like the oceanic plateau.

Read more: How rare minerals form when meteorites slam into Earth[8]

Our research shows these oceanic plateaus could have evolved to form the continents through a process known as crustal differentiation. The thick oceanic plateau formed from the impact can get hot enough at its base that it also melts, producing the kind of granitic rock that forms buoyant continental crust.

Are there other ways to make oceanic plateaus?

There are other ways oceanic plateaus can form. The thick crusts beneath Hawaii and Iceland formed not through giant impacts but “mantle plumes”, streams of hot material rising up from the edge of Earth’s metallic core, a bit like in a lava lamp. As this ascending plume reaches the lithosphere it triggers massive mantle melting to form an oceanic plateau.

So could plumes have created the continents? Based on our studies, and the balance of different oxygen isotopes in tiny grains of the mineral zircon, which is commonly found in tiny quantities in rocks from the continental crust, we don’t think so.

Zircon is the oldest known crustal material[9], and it can survive intact for billions of years. We can also determine quite precisely when it was formed, based on the decay of the radioactive uranium it contains.

What’s more, we can find out about the environment in which zircon formed by measuring the relative proportion of isotopes of oxygen[10] it contains.

We looked at zircon grains from one of the oldest surviving pieces of continental crust in the world, the Pilbara Craton in Western Australia, which started forming more than 3 billion years ago. Many of the oldest grains of zircon contained more light oxygen isotopes, which indicate shallow melting, but younger grains contain a more mantle-like balance isotopes, indicating much deeper melting.

Zircon δ18O (‰) vs age (Ma) for individual dated magmatic zircon grains from the Pilbara Craton. The horizontal grey band shows the array of δ18O in mantle zircon (5.3 +/– 0.6‰, 2 s.d.). The vertical grey bands subdivide the data into three stages, as discussed in the paper. The pink boxes represent the age of deposition of high-energy impact deposits (spherule beds) from the Pilbara Craton and more widely.

This “top-down” pattern of oxygen isotopes is what you might expect following a giant meteorite impact. In mantle plumes, by contrast, melting is a “bottom-up” process.

Sounds reasonable, but is there any other evidence?

Yes, there is! The zircons from the Pilbara Craton appear to have been formed in a handful of distinct periods, rather than continuously over time.

Except for the earliest grains, the other grains with isotopically-light zircon have the same age as spherule beds in the Pilbara Craton and elsewhere.

Spherule beds are deposits of droplets of material “splashed out” by meteorite impacts. The fact the zircons have the same age suggests they may have been formed by the same events.

The sun sets in the Pilbara, and the hunt for firewood is on. Chris Kirkland, 2021.

Further, the “top-down” pattern of isotopes can be recognised in other areas of ancient continental crust, such as in Canada and Greenland. However, data from elsewhere have not yet been carefully filtered like the Pilbara data, so it will take more work to confirm this pattern.

The next step of our research is to reanalyse these ancient rocks from elsewhere to confirm what we suspect – that the continents grew at the sites of giant meteorite impacts. Boom.

References

  1. ^ only planet we know of with continents (doi.org)
  2. ^ Earth’s biomass (www.pnas.org)
  3. ^ idea (www.nature.com)
  4. ^ several times (doi.org)
  5. ^ new research published in Nature (www.nature.com)
  6. ^ Kelvin Song / Wikimedia (en.wikipedia.org)
  7. ^ CC BY (creativecommons.org)
  8. ^ How rare minerals form when meteorites slam into Earth (theconversation.com)
  9. ^ oldest known crustal material (www.nature.com)
  10. ^ isotopes of oxygen (doi.org)

Read more https://theconversation.com/what-created-the-continents-new-evidence-points-to-giant-asteroids-185606

Times Magazine

Headless CMS in Digital Twins and 3D Product Experiences

Image by freepik As the metaverse becomes more advanced and accessible, it's clear that multiple sectors will use digital twins and 3D product experiences to visualize, connect, and streamline efforts better. A digital twin is a virtual replica of ...

The Decline of Hyper-Casual: How Mid-Core Mobile Games Took Over in 2025

In recent years, the mobile gaming landscape has undergone a significant transformation, with mid-core mobile games emerging as the dominant force in app stores by 2025. This shift is underpinned by changing user habits and evolving monetization tr...

Understanding ITIL 4 and PRINCE2 Project Management Synergy

Key Highlights ITIL 4 focuses on IT service management, emphasising continual improvement and value creation through modern digital transformation approaches. PRINCE2 project management supports systematic planning and execution of projects wit...

What AI Adoption Means for the Future of Workplace Risk Management

Image by freepik As industrial operations become more complex and fast-paced, the risks faced by workers and employers alike continue to grow. Traditional safety models—reliant on manual oversight, reactive investigations, and standardised checklist...

From Beach Bops to Alpine Anthems: Your Sonos Survival Guide for a Long Weekend Escape

Alright, fellow adventurers and relaxation enthusiasts! So, you've packed your bags, charged your devices, and mentally prepared for that glorious King's Birthday long weekend. But hold on, are you really ready? Because a true long weekend warrior kn...

Effective Commercial Pest Control Solutions for a Safer Workplace

Keeping a workplace clean, safe, and free from pests is essential for maintaining productivity, protecting employee health, and upholding a company's reputation. Pests pose health risks, can cause structural damage, and can lead to serious legal an...

The Times Features

Exploring the Curriculum at a Modern Junior School in Melbourne

Key Highlights The curriculum at junior schools emphasises whole-person development, catering to children’s physical, emotional, and intellectual needs. It ensures early year...

Distressed by all the bad news? Here’s how to stay informed but still look after yourself

If you’re feeling like the news is particularly bad at the moment, you’re not alone. But many of us can’t look away – and don’t want to. Engaging with news can help us make ...

The Role of Your GP in Creating a Chronic Disease Management Plan That Works

Living with a long-term condition, whether that is diabetes, asthma, arthritis or heart disease, means making hundreds of small decisions every day. You plan your diet against m...

Troubleshooting Flickering Lights: A Comprehensive Guide for Homeowners

Image by rawpixel.com on Freepik Effectively addressing flickering lights in your home is more than just a matter of convenience; it's a pivotal aspect of both home safety and en...

My shins hurt after running. Could it be shin splints?

If you’ve started running for the first time, started again after a break, or your workout is more intense, you might have felt it. A dull, nagging ache down your shins after...

Metal Roof Replacement Cost Per Square Metre in 2025: A Comprehensive Guide for Australian Homeowners

In recent years, the trend of installing metal roofs has surged across Australia. With their reputation for being both robust and visually appealing, it's easy to understand thei...