<blockquote>
<p>I know that continental crust has a granite composition while oceanic crust has a basalt composition.</p>
</blockquote>
<p>That's the key. Granitic rock has a significantly higher silicon composition compared to basaltic rock and has a significantly lower iron and magnesium composition compared to basaltic rock. This results in continental crust being less dense than oceanic crust. Cooling does not change the chemical composition.</p>

CC BY-SA 4.0
2023-08-14T06:21:49.113Z
2023-08-14T06:21:49.113Z
David Hammen
<p>With oceanic, older crust is denser because it is cooler (old=cold=dense=faster subduction).</p>
<p>Even when several millions of years old, the sheer thickness of the layer and the heat capacity of the rock require that there must be a lot of thermal energy locked up.</p>

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2023-08-14T17:59:28.317Z
2023-08-14T17:59:28.317Z
Bob Sjerunkel
<p>When we consider <strong>two oceanic</strong> crusts, the older oceanic crust is heavier and the newer oceanic crust is lighter.</p>
<p>But when we consider two crusts, one <strong>continental</strong> and the other <strong>oceanic</strong>, continental crust is the older one yet LIGHTER of the two; while oceanic crust, the newer one, is HEAVIER of the two.</p>
<p>Why is that?</p>
<p>I know that continental crust has a granite composition while oceanic crust has a basalt composition.</p>
<p>Hence, I am not sure if the question can be reduced to: &quot;<strong>Why is older basalt heavier than newer basalt?</strong>&quot; (iff that actually is the case)</p>

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2023-08-14T07:57:05.433Z
Highly related: https://earthscience.stackexchange.com/q/25460/18081
Jean-Marie Prival
<oceanography><plate-tectonics><ocean-ridge><oceanic-crust>
If among oceanic crusts older means heavier, then why is old continental crust lighter than new oceanic crusts?
Koushik Sarkar
# If among oceanic crusts older means heavier, then why is old continental crust lighter than new oceanic crusts?

(Asked by: username_0 on 2023-08-14)

When we consider **two oceanic** crusts, the older oceanic crust is heavier and the newer oceanic crust is lighter.

But when we consider two crusts, one **continental** and the other **oceanic**, continental crust is the older one yet LIGHTER of the two; while oceanic crust, the newer one, is HEAVIER of the two.

Why is that?

I know that continental crust has a granite composition while oceanic crust has a basalt composition.

Hence, I am not sure if the question can be reduced to: "**Why is older basalt heavier than newer basalt?**" (iff that actually is the case)

**Tags:** oceanography, plate-tectonics, ocean-ridge, oceanic-crust

> **Comments:**
> **username_1**: Highly related: https://earthscience.stackexchange.com/q/25460/18081  

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## 2 answers

### Answer by username_2 on 2023-08-14. Score: 5

> I know that continental crust has a granite composition while oceanic crust has a basalt composition.

That's the key. Granitic rock has a significantly higher silicon composition compared to basaltic rock and has a significantly lower iron and magnesium composition compared to basaltic rock. This results in continental crust being less dense than oceanic crust. Cooling does not change the chemical composition.


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### Answer by username_3 on 2023-08-14. Score: 0

With oceanic, older crust is denser because it is cooler (old=cold=dense=faster subduction).

Even when several millions of years old, the sheer thickness of the layer and the heat capacity of the rock require that there must be a lot of thermal energy locked up.


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