<h2>You forgot about continents</h2>

<p>First of all, it's necessary to point out the false premise in your question: It is <strong>not true</strong> that "all plates that are currently left are younger than Cretaceous".  There is a near-continuous record of rocks stretching all the way back to the <a href="https://en.wikipedia.org/wiki/Hadean" rel="nofollow noreferrer">Hadean</a> Eon 4 billion years ago.  And there are older crystals called <a href="https://en.wikipedia.org/wiki/Zircon#Radiometric_Dating" rel="nofollow noreferrer">zircon</a>s that are found as inclusions in younger rocks.  </p>

<p>The thing is, these rocks are on land, part of <a href="https://en.wikipedia.org/wiki/Continental_crust" rel="nofollow noreferrer">continental crust</a>. Your question seems to be unaware of the existence of  continental crust. Of course, since you're not currently sitting at the bottom of the ocean, you're on top of continental crust right now. Most of the big tectonic plates are part oceanic and part continental.</p>

<p>Continents have been built up little by little over geological time. Their rocks are a mixed-up jigsaw puzzle of various types and ages. It's the geologist's job to figure out how those pieces fit together.</p>

<p>Here's just a taste, and it doesn't even show the complexity of the puzzle in North America by a long shot:</p>

<p><img src="https://upload.wikimedia.org/wikipedia/commons/a/a7/North_america_basement_rocks.png" alt="basement rocks">
<em>(courtesy of <a href="https://www.usgs.gov/information-policies-and-instructions/copyrights-and-credits#copyright" rel="nofollow noreferrer">United States Geological Survey</a>, via <a href="https://commons.wikimedia.org/wiki/File:North_america_basement_rocks.png" rel="nofollow noreferrer">Wikimedia Commons</a>)</em></p>

<p>It is true that the oceanic plates are mostly destroyed by subduction, but the oceanic crust has to go beneath something, and that's often a continent. Besides, subduction helps make continents grow:</p>

<ul>
<li><p>not all of the rock is subducted: some seafloor sediments are scraped off and piled against continental margins</p></li>
<li><p>The top layers of rock that are subducted melt, and the melted rock bubbles its way up through the overlying crust, producing plutons and volcanic arcs. Sometimes these are on continents (such as the Cascades and Andes) so their rocks directly add mass to them.</p></li>
<li><p>When the volcanoes are out in the ocean, the subduction process pulls them into continents and they get cemented to the edge. Sometimes they form little mini- continents (such as Japan and New Zealand).</p></li>
</ul>

<p>The oldest oceanic crust currently at the seafloor is in the eastern Mediterranean. In <a href="https://www.nature.com/articles/ngeo2784" rel="nofollow noreferrer">an article in Nature Geoscience</a> Roi Granot of Ben-Gurion University of the Negev suggests that the [Herodotus Basin] is a remnant of ancient <a href="https://en.wikipedia.org/wiki/Tethys_Ocean" rel="nofollow noreferrer">Tethys Ocean</a>, having formed up to 340 Ma during the Early <a href="https://en.wikipedia.org/wiki/Carboniferous" rel="nofollow noreferrer">Carboniferous</a> period. Most oceanic crust is 200 million years old (Jurassic) or younger.  They're an important part of putting the puzzle together, but as I stated at the beginning of my answer, the geological record is <em>much</em> older, because of continental rocks.</p>

<p>Finally, there is really old oceanic crust in the form of <a href="https://en.wikipedia.org/wiki/Ophiolite" rel="nofollow noreferrer">ophiolites</a>, which are bits of oceanic crust that have been incorporated into continents.  Since they're no longer part of the oceanic conveyor belt, some can be quite old. The oldest is about 3.8 billion years old. </p>

CC BY-SA 4.0
2018-09-10T02:16:16.017Z
2018-09-14T00:57:33.857Z
2018-09-14T00:57:33.857Z
Spencer
<p>I have read that the oldest oceanic plate that we see today is from the Cretaceous period. If so, how do scientists reconstruct plate movements and continental structure pre Cretaceous? And aren't all fossils before Cretaceous lost?</p>

<p>Why are we able to deduct geology information pre Cretaceous? And what is the oldest period we are able to gain information from?</p>

CC BY-SA 4.0
2018-09-09T19:24:02.267Z
I'm glad you want to participate, but you have to tell us the source of your assumption that "the oldest oceanic plate that we see today is from Cretaceous period", which isn't true. Some oceanic crust dates back to the Permian, and some [ophiolites](https://en.wikipedia.org/wiki/Ophiolite) are as old as 3.8 billion years old. Finally, geological history is reconstructed from rocks in [continental crust](https://en.wikipedia.org/wiki/Continental_crust), and these show a full history with even some rocks from the late Hadean, 4 billion years ago.
Spencer
CC BY-SA 4.0
2018-09-09T19:55:21.180Z
@Universal_Learner The rocks under the eastern Mediterranean are of Permian age.  There are also very old ophiolites, which are arguably oceanic crust.  Anyway that's a side issue; the title asserts that "all plates that are currently left" are that young.
Spencer
CC BY-SA 4.0
2018-09-09T22:55:04.787Z
I think I might be mistaken then, I went back to the post I found and see that the author of the post did indeed mentioned pacific ocean plate instead of all tetonic plate. So is the Permian period the oldest plate we can see currently, if so is there techniques to deduct what happen geologically before the oldest plate we can excavate ?
Jal
CC BY-SA 4.0
2018-09-10T00:24:58.077Z
@Spencer would you like to expand your comments to an answer?
Gimelist
<plate-tectonics><continent>
How do scientists reconstruct pre Cretaceous continent if all plates that are currently left are younger than Cretaceous?
Jal
# How do scientists reconstruct pre Cretaceous continent if all plates that are currently left are younger than Cretaceous?

(Asked by: username_0 on 2018-09-09)

I have read that the oldest oceanic plate that we see today is from the Cretaceous period. If so, how do scientists reconstruct plate movements and continental structure pre Cretaceous? And aren't all fossils before Cretaceous lost?

Why are we able to deduct geology information pre Cretaceous? And what is the oldest period we are able to gain information from?

**Tags:** plate-tectonics, continent

> **Comments:**
> **username_1**: I'm glad you want to participate, but you have to tell us the source of your assumption that "the oldest oceanic plate that we see today is from Cretaceous period", which isn't true. Some oceanic crust dates back to the Permian, and some [ophiolites](https://en.wikipedia.org/wiki/Ophiolite) are as old as 3.8 billion years old. Finally, geological history is reconstructed from rocks in [continental crust](https://en.wikipedia.org/wiki/Continental_crust), and these show a full history with even some rocks from the late Hadean, 4 billion years ago.  
> **username_1**: @Universal_Learner The rocks under the eastern Mediterranean are of Permian age.  There are also very old ophiolites, which are arguably oceanic crust.  Anyway that's a side issue; the title asserts that "all plates that are currently left" are that young.  
> **username_0**: I think I might be mistaken then, I went back to the post I found and see that the author of the post did indeed mentioned pacific ocean plate instead of all tetonic plate. So is the Permian period the oldest plate we can see currently, if so is there techniques to deduct what happen geologically before the oldest plate we can excavate ?  
> **username_2**: @username_1 would you like to expand your comments to an answer?  

---

## 1 answers

### Answer by username_1 on 2018-09-10. Score: 8 | Accepted answer

## You forgot about continents

First of all, it's necessary to point out the false premise in your question: It is **not true** that "all plates that are currently left are younger than Cretaceous". There is a near-continuous record of rocks stretching all the way back to the [Hadean](https://en.wikipedia.org/wiki/Hadean) Eon 4 billion years ago. And there are older crystals called [zircon](https://en.wikipedia.org/wiki/Zircon#Radiometric_Dating)s that are found as inclusions in younger rocks.

The thing is, these rocks are on land, part of [continental crust](https://en.wikipedia.org/wiki/Continental_crust). Your question seems to be unaware of the existence of continental crust. Of course, since you're not currently sitting at the bottom of the ocean, you're on top of continental crust right now. Most of the big tectonic plates are part oceanic and part continental.

Continents have been built up little by little over geological time. Their rocks are a mixed-up jigsaw puzzle of various types and ages. It's the geologist's job to figure out how those pieces fit together.

Here's just a taste, and it doesn't even show the complexity of the puzzle in North America by a long shot:

![basement rocks](https://upload.wikimedia.org/wikipedia/commons/a/a7/North_america_basement_rocks.png)
*(courtesy of [United States Geological Survey](https://www.usgs.gov/information-policies-and-instructions/copyrights-and-credits#copyright), via [Wikimedia Commons](https://commons.wikimedia.org/wiki/File:North_america_basement_rocks.png))*

It is true that the oceanic plates are mostly destroyed by subduction, but the oceanic crust has to go beneath something, and that's often a continent. Besides, subduction helps make continents grow:

* not all of the rock is subducted: some seafloor sediments are scraped off and piled against continental margins
* The top layers of rock that are subducted melt, and the melted rock bubbles its way up through the overlying crust, producing plutons and volcanic arcs. Sometimes these are on continents (such as the Cascades and Andes) so their rocks directly add mass to them.
* When the volcanoes are out in the ocean, the subduction process pulls them into continents and they get cemented to the edge. Sometimes they form little mini- continents (such as Japan and New Zealand).

The oldest oceanic crust currently at the seafloor is in the eastern Mediterranean. In [an article in Nature Geoscience](https://www.nature.com/articles/ngeo2784) Roi Granot of Ben-Gurion University of the Negev suggests that the [Herodotus Basin] is a remnant of ancient [Tethys Ocean](https://en.wikipedia.org/wiki/Tethys_Ocean), having formed up to 340 Ma during the Early [Carboniferous](https://en.wikipedia.org/wiki/Carboniferous) period. Most oceanic crust is 200 million years old (Jurassic) or younger. They're an important part of putting the puzzle together, but as I stated at the beginning of my answer, the geological record is *much* older, because of continental rocks.

Finally, there is really old oceanic crust in the form of [ophiolites](https://en.wikipedia.org/wiki/Ophiolite), which are bits of oceanic crust that have been incorporated into continents. Since they're no longer part of the oceanic conveyor belt, some can be quite old. The oldest is about 3.8 billion years old.


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