Questions tagged [geochemistry]

The science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems.

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Why is Earth's age given by dating meteorites rather than its own rocks?

Reading a course on Precambrian, I read that: Earth Age (around 4.5 billion years) is dated thanks to the meteorites hitting Earth during its formation rather than the inner materials composing the ...
Chirac's user avatar
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13 votes
1 answer
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What are the high field strength and large ion lithophile (HFS or HFSE & LIL or LILE) elements?

There are two groups of elements that are frequently mentioned when discussing incompatible trace elements. They are the high field strength elements (HFS or HFSE) and the large ion lithophile ...
Gimelist's user avatar
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9 votes
2 answers
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Will the sea get saltier forever?

The sea wasn't always salty. It's been getting saltier over millions of years as minerals dissolve. Is there a natural limit to this process, or the will the sea keep getting saltier forever? Is there ...
spraff's user avatar
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5 votes
1 answer
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Why is uranium only in the crust, really?

As I know, uranium is currently thought that it is mainly in the crust and not in the core or in the mantle. The reason for that it is a siderophile element which means it won't be solved in molten ...
peterh's user avatar
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20 votes
3 answers
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What are rare earths and why do they cluster near alkaline magmatism?

'Rare earths' play a vital role in the modern economy, and they are becoming more of a point of focus in geopolitical realms. What are 'rare earths' and why do they appear to cluster in association ...
DrewP84's user avatar
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18 votes
2 answers
852 views

Why is there Uranium in Earth's Crust?

Uranium's density is greater than most elements, so you would expect it to settle to the bottom of a volume of fluid. In the case of the Earth, which was molten in the beginning, you might then expect ...
Danubian Sailor's user avatar
16 votes
3 answers
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What processes produced the basalt columns of the Giant's Causeway?

The Giant's Causeway is, according to the Wikipedia page was formed during during the Paleogene Period, Antrim was subject to intense volcanic activity, when highly fluid molten basalt intruded ...
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6 votes
2 answers
851 views

What was the likely composition of Earth's early crust (how did crustal composition evolve)?

Was the first crust entirely mafic (oceanic) crust which was later distilled via volcanic arcs along subduction zones to make felsic rocks or did the earth start with bits of felsic crust? Are the ...
Inkenbrandt's user avatar
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5 votes
3 answers
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Why silicon is abundant in earth surface?

What is the reason for having silicon in so large quantity on earth surface?
ga1406's user avatar
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36 votes
5 answers
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How do we know the asteroids formed at the same time as earth?

In continuation of the question Why is Earth's age given by dating meteorites rather than its own rocks?, what evidence do we have that the asteroids indeed formed at the same time as earth? Is there ...
Nathaniel Bubis's user avatar
27 votes
5 answers
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What is the origin of the dominant atmospheric nitrogen content in Earth's atmosphere?

Comparing the atmospheric compositions of Earth with our nearest neighbours: As the table shows, the Earth's atmospheric nitrogen concentration is 78%, compared to 3.8% for Venus and 2.7% for Mars ...
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22 votes
2 answers
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What is the origin of the ocean's salt?

We know we cannot live without salt, but an investigation into the origins of ocean's salt leads one to believe that this issue is not fully resolved yet. What geological phenomenon caused the earth ...
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21 votes
6 answers
23k views

What was the first rock in the rock cycle?

I am an undergraduate student but I am a tutor at a High School, and one student asked me. Attempting to explain the rock cycle "if one rock turns into the other then which came first" my gut is ...
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15 votes
3 answers
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What, if any, paleoclimate data can be derived from igneous rocks?

Paleoclimate data often derives from sedimentary rocks. Metamorphic rocks can also contribute to paleoclimate information in a wide variety of ways. What about igneous rocks? I guess that this can ...
Gimelist's user avatar
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7 votes
1 answer
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Why is calcium so much more abundant in/on Earth's crust (and oceans) than it is elsewhere? (relatively speaking...)

Inside the entire Earth as a whole, and throughout our Solar System and galaxy, etc., magnesium is at least 14 times (or more) as common as calcium, atom-per-atom. But, on Earth's crust and oceans, ...
Kurt Hikes's user avatar
6 votes
1 answer
4k views

The effect of CO2 concentration on the pH of the ocean

I'm confused about how increased $\ce{CO2}$ concentration in the atmosphere affects the pH of the ocean. The increase in $\ce{CO2}$ concentration means the pH of the ocean will decrease (by several ...
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4 votes
1 answer
841 views

What are the implications of the recent discovery that huge oceans exist close to the mantle of the Earth? [duplicate]

I was of the notion that as we get deeper into the Earth, it gets hotter and hotter. If so, how can there be huge oceans (they seem bigger than our Pacific) exist at such a place? If so, what are the ...
user3736290's user avatar
2 votes
1 answer
252 views

Why the "Mission to Earth’s core" proposal suggests using liquid iron instead of lead?

Nature communications article "Mission to Earth's core — a modest proposal", suggests placing a large volume of liquid iron in a crack and let it sink all the way to the Earth's core, carrying along a ...
Camilo Rada's user avatar
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2 votes
2 answers
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Melting point of minerals

Looking at this website, I can see the melting point of the following minerals: http://hyperphysics.phy-astr.gsu.edu/hbase/Geophys/meltrock.html Apparently at a temperature of 1200 °C, all the ...
Neeraj Kulkarni's user avatar
35 votes
5 answers
11k views

How and why did the oceans form on Earth but not on other planets?

Earth is the only planet in our solar system that has copious amounts of water on it. Where did this water come from and why is there so much water on Earth compared to every other planet in the ...
Kenshin's user avatar
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19 votes
3 answers
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Is the magma in one volcano different from the magma in every other volcano?

First off, a confession: I'm asking this question because of The Lord of the Rings. If you're not aware already, in the story, a magical ring can only be destroyed in a specific volcano. The reason ...
Wad Cheber's user avatar
19 votes
3 answers
3k views

Why does Earth have abundant oxygen in the atmosphere?

Because of photosynthesis, obviously. But then it's not actually that obvious after all, because photosynthesis is mostly balanced by respiration. We can summarise the processes of photosynthesis ...
N. Virgo's user avatar
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17 votes
2 answers
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How much Uranium is there in the Earth's Crust?

Are there any estimates of the amount of Uranium there is in Earth's Crust? From what I know, it's supposed that there are large amounts of Uranium in Earth's Core, the decay of which is responsible ...
Danubian Sailor's user avatar
16 votes
1 answer
575 views

When a tectonic plate subducts, does any of the subducted material melt, or is it just the mantle above the subducted slab that melts?

I know that water released from oceanic crust causes melting of the mantle in subduction zones, but does any part of the subducted slab melt as well - such as the sediments on the slab or the basalt? ...
Inkenbrandt's user avatar
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13 votes
1 answer
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What is it about ancient craton geology that results in associated kimberlite pipes containing economic diamond deposits?

According to the Australian Geological Survey Organisation paper Kimberlite and lamproite diamond pipes (Jaques, 1998), economic deposits of volcanically-formed diamonds are restricted to ancient ...
user avatar
13 votes
2 answers
233 views

Are there any metal anomalies other than iridium in the K-Pg boundary?

The iridium anomaly marks the elevated concentration of iridium in sedimentary deposits of the Cretaceous-Paleogene boundary. The iridium is said to come from the impactor, which is supposed to have ...
Gimelist's user avatar
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12 votes
1 answer
515 views

Are there significant amounts of rare earth elements on Iceland?

The rare earth elements form in magmatic rocks. The Iceland is very active vulcanic region, and it's, to my knowledge, entirely build from magmatic rocks. So it wouldn't be surprising if there were ...
Danubian Sailor's user avatar
12 votes
3 answers
436 views

Nuclear testing and the Anthropocene, a chemostratigraphic link?

The Anthropocene is described by Wikipedia as an informal geologic chronological term for the proposed epoch that began when human activities had a significant global impact on the Earth's ...
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11 votes
1 answer
272 views

How can scientists be confident of isotope ratios in past eras and varied locations, used for radiometric dating?

Radiometric dating relies on past isotope ratio predictions being very reliable. However, this is not necessarily so. For example, in Uranium forensics, 235U and 238U ratios are about the same for ...
497362's user avatar
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10 votes
5 answers
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Why is continental crust less dense than oceanic?

Why is it that continental crust is less dense than oceanic, where in fact continental crust is thicker than oceanic crust?
Joerico's user avatar
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10 votes
0 answers
95 views

Predicting volcanic eruptions by experimentally proven volatile outgassing observations

In the abstract for the article Forecasting Etna eruptions by real-time observation of volcanic gas composition (Aiuppa et al. 2007), the authors assert that real time monitoring of volcanic volatiles,...
user avatar
10 votes
2 answers
1k views

Composition of Martian Crust

Does the composition of the crust of Mars roughly correspond to that of the crust of Earth. That is, is the elemental abundance in decreasing order silicon, oxygen, aluminum, etc.?
wogsland's user avatar
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9 votes
2 answers
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Is oxygen the most abundant element on Earth?

When I was in school, I was taught that we need oxygen to breathe, but it actually constitutes only a small fraction of the atmospheric composition, and that nitrogen constituted the largest fraction ...
Matthew Layton's user avatar
9 votes
1 answer
311 views

Did an impact crater influence the formation of uranium deposits in South Australia?

As a supplementary question Did an impact crater cause the formation of the gas fields in north eastern South Australia . South Australia is a well documented uranium province. Could an impact crater, ...
Fred's user avatar
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9 votes
1 answer
551 views

How does the composition of volcanic rock change as it makes its ascent towards the surface?

A schematic for the fluid mechanics of a volcano is represented below. Graciously borrowed from Figure 1 of the reference cited below From the caption of that figure: During explosive eruptions, ...
jonsca's user avatar
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8 votes
2 answers
2k views

Do lead 206 and other daughter isotopes occur naturally?

I am reading studies about the age of the earth and U-238 to Pb-206 comes up a lot. My question is: In meteorites, or really anywhere, is lead 206 natural or does it always come from radioactive decay?...
Beans's user avatar
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8 votes
1 answer
682 views

Release mechanism for methane clathrate at the PETM

The Paleocene-Eocene Thermal Maximum (PETM) is a well-studied warming event near the Paleocene-Eocene boundary. It is characterized by its extreme warming rate: from onset to recovery the event lasted ...
plannapus's user avatar
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8 votes
1 answer
969 views

What "g" would be needed to keep helium on Earth?

I know that helium is a very light and rare gas on Earth because Earths gravity is not strong enough to keep it. Instead, helium and hydrogen are rising through the atmosphere and escape into outer ...
Petr Hykš's user avatar
7 votes
1 answer
122 views

What is the geochemical source for the helium detected in deep Arctic explosive eruptions?

Recently, there has been explosive deep-ocean volcanism detected along the slowly-spreading Gakkel Ridge in the Arctic Ocean (see map below), according the National Geographic news article Arctic ...
user avatar
7 votes
1 answer
491 views

What ozone depleting chemicals can salt produce?

According to How Long Will Life Last On Earth, 250 million years ago Siberia underwent a large a prolonged period of volcanic activity. It has been speculated that large salt deposits that existed in ...
Fred's user avatar
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7 votes
1 answer
2k views

How do hematite and magnetite form?

I want to understand the conditions under which hematite $\ce{Fe_2O_3}$ and magnetite $\ce{Fe_3O_4}$ form in nature. The linked Wikipedia articles explain various conditions under which they form, but ...
Tyler Durden's user avatar
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6 votes
2 answers
844 views

Why doesn't the Earth's outer core dissolve into the mantle?

It is well accepted that the outer core is made out of liquid iron and nickel, and as everything else it should tend to reach chemical equilibrium with its surrounding. In particular, I would expect ...
Camilo Rada's user avatar
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5 votes
2 answers
218 views

Why does calcium occur together with felsic rocks and magnesium with mafic rocks if calcium is denser than magnesium?

Felsic rocks contain a lot of sodium, potassium and calcium (and a great deal of aluminum), while mafic rocks consist of a lot of magnesium with iron.... Why is this? Why is magnesium (z=12) in the ...
Kurt Hikes's user avatar
5 votes
2 answers
732 views

Where does molecular hydrogen in the atmosphere come from?

This figure from Wikipedia's Atmosphere of Earth shows a hydrogen fraction of 0.000055 percent by volume. Question: Where does molecular hydrogen in the atmosphere come from? Does this come directly ...
uhoh's user avatar
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4 votes
1 answer
77 views

Phosphate in the oceans, does it tend to bond with sodium?

Phosphate has a major role in biology and the biosphere. In its "abiotic" form, floating around in the oceans, lets say marine oceans to be specific, does it tend to be in the Na3PO4 form? ...
ElnorCat's user avatar
4 votes
1 answer
87 views

Likely air composition in cave only accessible from underwater?

I recently stumbled on the images of the Cosquer cave, located in France, famous for being a comparatively recently discovered as a Paleolithic decorated cave. The entrance to cave now is more than ...
Gnudiff's user avatar
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4 votes
1 answer
5k views

What is the difference between chalcophile and siderophile elements?

As it is described (W. M. White, Geochemistry): Siderophile elements have an affinity for a metallic liquid phase and chalcophile elements have an affinity for a sulfide liquid phase. What ...
marianess's user avatar
3 votes
0 answers
76 views

Can $\ce{CaCO3}$ shells contribute to $\ce{CO2}$ emissions in volcanoes within subduction zones?

CaCO3 dissolves below the Carbonate Compensation Depth (CCD). However, this paper suggests that some CaCO3 can exist below the CCD. My question arises from a discussion in this answer. The question is ...
user avatar
2 votes
3 answers
7k views

Are fossil fuels really formed from fossils?

Hydrocarbons have been found in great abundance elsewhere in the solar system where there is unlikely to be evidence for life past or present. No fossils involved. Petroleum and natural gas wells ...
0tyranny0poverty's user avatar
2 votes
1 answer
81 views

How does friction and radiolysis provide hydrogen for "unusual types of methane"?

The fascinating New York Times article Gas That Makes a Mountain Breathe Fire Is Turning Up Around the World talks about the Flames of Chimaera and the Deep Carbon Observatory: And a series of ...
uhoh's user avatar
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