Have you ever wondered why we have dry land on Earth? It might seem obvious that without water, there wouldn’t be any lakes, rivers, or oceans, and therefore no dry land. But there’s more to it than that. Without water, our continents wouldn’t even exist!
The continents are mostly made up of a type of rock called granite. Granite is a lightweight igneous rock, which means it’s formed from cooled magma. Because it’s lighter than other rocks, granite can pile up high to form continents without sinking into the Earth. But how does this lightweight rock come to be?
To understand how granite forms, we need to look beneath the ocean. Deep ocean trenches are places where two tectonic plates meet, and one plate sinks beneath the other. Long ago, ocean water seeped into the seafloor and became part of the rocks there. When these rocks dive deep into the Earth, the heat and pressure cause the water to be squeezed out. This water lowers the melting temperature of the surrounding rocks, allowing some of the lighter minerals to melt and form low-density magma.
This buoyant magma rises toward the Earth’s surface, eventually forming mountain chains made of granite. You can see examples of these new continental crusts along the Ring of Fire, like the Mariana Islands, Japan, and the Aleutian Islands. While these mountain chains aren’t full continents yet, over time, they can become part of larger landmasses.
As tectonic plates move, the dense seafloor beneath these island chains sinks into the Earth, but the lighter granite gets scraped onto existing continents. This process has been happening for millions of years, gradually building the continents we live on today, one piece at a time. So, in a way, we owe our continents to the oceans!
This fascinating process of continental formation is brought to you by 80,000 Hours, a nonprofit organization dedicated to helping people make a positive impact through their careers. With an average career lasting 80,000 hours, it’s a great opportunity to make a difference in the world.
80,000 Hours offers resources like guides for high-impact careers, a job board with meaningful roles, and a podcast featuring experts. They even discuss important topics like mental health challenges in careers. Best of all, their resources are free! Visit their website at 80000hours.org/minuteearth to get a free career guide and sign up for their newsletter.
Explore the process of granite formation by creating a simple model. Use clay to represent the Earth’s crust and a mixture of sand and small pebbles to simulate the lighter minerals. Heat the mixture gently with a lamp to mimic the heat and pressure beneath the Earth’s surface. Observe how the lighter materials rise, similar to how granite forms.
Engage with the concept of tectonic plates by assembling a puzzle of the Earth’s plates. Use a world map and cut out the continents and oceanic plates. Try to fit them together, simulating how they move and interact. Discuss how these movements contribute to the formation of continents.
Participate in a role-playing game where you act as tectonic plates. Assign roles to different students as plates, ocean water, and magma. Move around the classroom to simulate the process of subduction, water seepage, and magma formation. This will help you understand the dynamic nature of Earth’s crust.
Conduct a research project on the Ring of Fire. Investigate the geological activity in this area and how it contributes to the formation of new continental crusts. Present your findings in a creative format, such as a poster or a digital presentation.
Visit the 80,000 Hours website and explore careers related to geology and environmental science. Identify a career that interests you and create a plan outlining the steps you would take to pursue it. Share your plan with the class and discuss how you can make a positive impact through your career choice.
Here’s a sanitized version of the provided YouTube transcript:
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We couldn’t have dry land without water. You might be thinking, obviously, because if Earth didn’t have any water on it – no lakes, no rivers, no oceans – the whole idea of “dry land” would be pretty meaningless. But that’s not what I mean; I mean that, without water, our continents simply wouldn’t exist.
There are all kinds of rock on the continents, but the vast bulk of continental crust – the part of Earth’s rocky outer layer that isn’t the seafloor – is made of granite, a relatively lightweight igneous rock. The lightweight nature of granite is the whole reason continental crust can pile up way higher than the seafloor without sinking, but it’s kind of surprising that so much of this low-density rock exists at all.
That’s because granite is formed when rock deep in the planet melts and re-cools, but the material down there isn’t like granite at all; it’s much denser. So how does granite turn out so lightweight? Ironically, we’re able to keep our toes dry thanks to what’s happening beneath the ocean: this black crack here is a deep ocean trench, where two tectonic plates are colliding, and one is sinking down into the planet.
And here’s where water comes in: long ago, ocean water seeped into the seafloor and became part of the rock’s mineral structure. Now, as the seafloor begins diving into the planet, the intense heat and pressure hundreds of kilometers below the surface sort of squeeze a lot of the water back out, and this water has a unique effect: it lowers the melting temperature of the surrounding rock just enough to melt some of the lightest minerals, creating pockets of low-density magma.
This buoyant magma makes its way up toward Earth’s surface, eventually creating mountain chains of granite. Take a spin along the Ring of Fire and you can see these piles of new continental crust – for example, there are the Mariana Islands, Japan, and the Aleutian Islands. Of course, these mountain chains aren’t continents yet – they’re just scraps of continental crust – but it’s only a matter of (a very long) time until the plate they are riding on crashes into another plate carrying larger chunks of continent.
At that point, the dense seafloor these island chains are sitting on will plunge into the planet, but thanks to their relatively low density, the heaps of granite will simply get scraped onto the existing landmass. The continents we live on today were largely assembled this way, one pile of rock at a time. In other words, it’s thanks to our oceans that we can take our continents for granted.
This video is brought to you by 80,000 Hours – which we’re pretty excited about. That’s because 80,000 Hours is a nonprofit whose sole purpose is to help people use their careers to make a positive impact on the world. Your career is on average 80,000 hours long, so it’s a pretty big opportunity to make a difference.
80,000 Hours provides resources including guides on how to have a high-impact career, a curated job board with hundreds of high-impact roles, and even a podcast featuring interesting guests, including experts who already have careers in these areas. I especially appreciated the thoughtful episode where they discuss navigating a career through challenges like depression, impostor syndrome, and other mental health issues.
And all their resources are free – all they want is to help you make a difference. Click our link in the description or go to 80000hours.org/minuteearth to receive a free copy of their in-depth career guide, as well as to sign up for their newsletter to get updates on their research and new job opportunities.
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This version maintains the original meaning while removing any informal language or phrases that could be considered inappropriate.
Continents – Large landmasses on Earth’s surface that are separated by oceans. – Africa and Asia are two of the seven continents on Earth.
Granite – A common type of intrusive, igneous rock that is granular and phaneritic in texture. – The mountains in the region are primarily composed of granite, which is very durable.
Water – A transparent, tasteless, odorless, and nearly colorless chemical substance that is essential for all known forms of life. – Water covers about 71% of Earth’s surface, mostly in seas and oceans.
Tectonic – Relating to the structure of the Earth’s crust and the large-scale processes that take place within it. – The tectonic plates are constantly moving, which can cause earthquakes.
Magma – Molten rock beneath the Earth’s surface. – When magma erupts from a volcano, it is called lava.
Ocean – A large body of saltwater that covers most of Earth’s surface and surrounds its continents. – The Pacific Ocean is the largest and deepest of Earth’s oceanic divisions.
Crust – The outermost layer of Earth, composed of rock, that forms the continents and ocean floors. – The Earth’s crust is broken into several large tectonic plates.
Islands – Landforms that are completely surrounded by water. – The Hawaiian Islands were formed by volcanic activity in the Pacific Ocean.
Mountains – Large landforms that rise prominently above their surroundings, typically having steep slopes and a significant elevation difference. – The Rocky Mountains stretch over 3,000 miles from Canada to New Mexico.
Density – The measure of mass per unit volume of a substance. – The density of oceanic crust is greater than that of continental crust, which is why it sits lower in the mantle.
