<p>Does look a bit like a homework question..</p>

<h1>First rock</h1>

<p>Igneous rocks would have formed first, obviously, although if we consider the pre-Mars-forming collision Earth, then the process of cold accretion could have initially formed metamorphic rocks at the center of the early <a href="https://www.universetoday.com/37116/planetoid/" rel="nofollow noreferrer">planetoid</a>..</p>

<p>And that planetoid would have to be considered sedimentary, formed out of dust particles.</p>

<p>So what the first rock is depends on how you define Earth, or the point at which a specific planetoid would be positively identified as Earth.</p>

<h1>Oldest Rock</h1>

<p>First, are we talking about the oldest identifiable mineral grain (<a href="https://www.livescience.com/43584-earth-oldest-rock-jack-hills-zircon.html" rel="nofollow noreferrer">Zircons, about 4.4 billion years old</a>), or the oldest complete rock (<a href="https://en.wikipedia.org/wiki/Isua_Greenstone_Belt" rel="nofollow noreferrer">Isua Greenstone Belt, Greenland</a>, 3.8 billion years). The first may qualify as part of a sedimentary rock, the second is metamorphic - but with a volcanic original rock.</p>

<p>And, of course, there could well be a meteorite out there - yet to be discovered or dated - that originates from <a href="http://www.sciencemag.org/news/2018/03/mysterious-asteroid-visited-us-beyond-our-solar-system-probably-came-place-two-stars" rel="nofollow noreferrer">outside the solar system</a> and is therefore older than the solar system. That would qualify as the oldest rock on the planet.</p>

CC BY-SA 4.0
2018-10-30T15:25:09.527Z
2018-10-30T15:25:09.527Z
Andrew Jon Dodds
<p>It could be sedimantary or metamorphic rock or intrusive igneous rock</p>

CC BY-SA 4.0
2018-10-29T18:54:34.307Z
I think it's safe to assume you're asking about whatever rocks formed after the Theia-Earth impact, since anything that formed before that would have been obliterated. Since the Earth was all magma ocean after that impact, the first rocks would had to have been basalt. Sedimentary rocks couldn't have formed until well after the oceans formed, and intrusive igneous rocks, until there was a crust for the magma to intrude into.
BillDOe
CC BY-SA 4.0
2018-10-29T21:45:34.113Z
Why do you give those 3 suggestions?
Jan Doggen
<planetology>
What type of rock formed first on earth and which rock is the oldest?
Savagecas23
# What type of rock formed first on earth and which rock is the oldest?

(Asked by: username_0 on 2018-10-29)

It could be sedimantary or metamorphic rock or intrusive igneous rock

**Tags:** planetology

> **Comments:**
> **username_1**: I think it's safe to assume you're asking about whatever rocks formed after the Theia-Earth impact, since anything that formed before that would have been obliterated. Since the Earth was all magma ocean after that impact, the first rocks would had to have been basalt. Sedimentary rocks couldn't have formed until well after the oceans formed, and intrusive igneous rocks, until there was a crust for the magma to intrude into.  
> **username_2**: Why do you give those 3 suggestions?  

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## 1 answers

### Answer by username_3 on 2018-10-30. Score: 1

Does look a bit like a homework question..

# First rock

Igneous rocks would have formed first, obviously, although if we consider the pre-Mars-forming collision Earth, then the process of cold accretion could have initially formed metamorphic rocks at the center of the early [planetoid](https://www.universetoday.com/37116/planetoid/)..

And that planetoid would have to be considered sedimentary, formed out of dust particles.

So what the first rock is depends on how you define Earth, or the point at which a specific planetoid would be positively identified as Earth.

# Oldest Rock

First, are we talking about the oldest identifiable mineral grain ([Zircons, about 4.4 billion years old](https://www.livescience.com/43584-earth-oldest-rock-jack-hills-zircon.html)), or the oldest complete rock ([Isua Greenstone Belt, Greenland](https://en.wikipedia.org/wiki/Isua_Greenstone_Belt), 3.8 billion years). The first may qualify as part of a sedimentary rock, the second is metamorphic - but with a volcanic original rock.

And, of course, there could well be a meteorite out there - yet to be discovered or dated - that originates from [outside the solar system](http://www.sciencemag.org/news/2018/03/mysterious-asteroid-visited-us-beyond-our-solar-system-probably-came-place-two-stars) and is therefore older than the solar system. That would qualify as the oldest rock on the planet.


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