Why are there still heavy elements in the earth's crust?

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In summary, during the early Earth's melting, the heavy elements such as iron sank into the core due to gravity and being insoluble in molten rock. However, uranium, being a lithophile element, stayed in the crust. This explains why we still have a lot of uranium deposits in the Earth's crust even though the theory suggests that the heat energy for the melt was due to radioactive decay. Additionally, comet and meteor bombardment also brought heavy elements like iridium to the outer crust, as seen in the Chicxulub crater dating back to ~64 million years ago.
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jr1956
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When the early Earth melted, the heavy elements were drawn to the center due to gravity. Thus we have a iron core. Why shouldn't the core also have drawn in the heavy elements like uranium? The theory says the heat energy for the melt was due to the radioactive decay Why do we still have a lot of deposits of Uranium in the Earth's crust?
 
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Separation was never perfect - we still have plenty of iron in the crust, even if the majority went down to the core.
 
  • #3
Later comet and meteor bombardment also brought heavy elements to the outer crust. For example: the Chicxulub crater, dating ~64 million years ago, contains shocked quartz with the element iridium in it.

http://en.wikipedia.org/wiki/Chicxulub_Crater
 
  • #4
jr1956 said:
When the early Earth melted, the heavy elements were drawn to the center due to gravity. Thus we have a iron core.
Iron sank into core not only because it is heavy but because it is insoluble/immiscible in molten rock (and heavier than rock).
jr1956 said:
Why shouldn't the core also have drawn in the heavy elements like uranium? The theory says the heat energy for the melt was due to the radioactive decay Why do we still have a lot of deposits of Uranium in the Earth's crust?

Because, although heavy, uranium is a lithophile - it is chemically active, forms oxides and silicates and dissolves in molten rocks. So uranium and thorium stayed in rocks.

Chemically inactive heavy elements, like gold, platinum and iridium, do preferentially dissolve in iron - which is why they did mainly sink into core, and this is why they are rare/expensive near surface.

Look at water - rock salt is heavier than raw flesh or waterlogged wood. Yet flesh and wood are insoluble and sink - but once salt is dissolved in water, it absolutely will not sink out of water.
 
  • #5
Thank you for your answers. I had thought about the meteorite angle, but no the lithophile characteristic of Uranium. Good analogy with the salt water.
 

1. Why are heavy elements found in the earth's crust?

The earth's crust is made up of various elements, including heavy elements, due to the process of differentiation during the earth's formation. During this process, heavier elements sank towards the earth's core, while lighter elements rose towards the surface. This resulted in the crust containing a mixture of elements, including heavy ones.

2. How did heavy elements form in the first place?

Heavy elements are formed through nuclear fusion reactions in the cores of stars. As stars age and run out of lighter elements to fuse, they begin fusing heavier elements, such as carbon, oxygen, and iron. When these stars eventually die and explode, they release heavy elements into the universe, which then become incorporated into planets like Earth.

3. Are there still heavy elements being formed on Earth?

No, the formation of heavy elements on Earth is a slow process that occurred billions of years ago. However, some heavy elements, such as uranium and thorium, have long half-lives and continue to decay into other elements, contributing to the presence of heavy elements in the earth's crust.

4. Are heavy elements evenly distributed in the earth's crust?

No, heavy elements are not evenly distributed in the earth's crust. The concentration of heavy elements varies depending on the location and geological processes that have occurred in that area. For example, areas with volcanic activity may have higher concentrations of heavy elements due to the melting and mixing of different layers of the earth's crust.

5. What role do heavy elements play in the earth's crust?

Heavy elements play a crucial role in the earth's crust. They make up important minerals and compounds, such as feldspar, quartz, and calcite, which are essential for the formation of rocks and soils. Heavy elements also play a role in various geological processes, such as the formation of mountains and the movement of tectonic plates.

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