Question 1

This PDF of the Earth's crust, while informative, confuses me a bit now because it appears to misrepresent facts, namely that if the Earth's core is mostly iron and nickel I would expect there to be more than traces of these elements. And if we have so much water (H2O) I would expect there to be higher than 0.15% of Hydrogen, unless we're not counting water as part of the Earth's crust. Also, what about the Earth's atmosphere? 
I'm thinking this view is too narrow-minded and puts things out of perspective.

Accepted Answer

I think the key here is that the infographic is talking about the elements that compose the Earth's crust, which doesn't include the water on top of the crust, or the atmosphere above it. It's not a misrepresentation; it just has a particular focus. As for nickel and iron, you're right that the core is mostly nickel and iron, but that's because these very dense elements sank to the center of the Earth while the entire planet was still molten--leaving much less near the surface of the Earth to go into the crust.

Question 2

why does the earth's crust compose of so many other elements

Accepted Answer

The reason of why the earth was composed of so many other elements other than hydrogen and helium is that the earth was a rocky planet.when the rocky planet was in the process of accretion,our sun ejected a flow called stellar wind.The stellar wind is so strong that it has blown away the lighter elements around the earth ,such as hydrogen and helium .And so the result turns out that only the heavier elements, such elements is the elements that we now have ,was gragually generated our dear homeplanet earth.Hopefully it will help you.

Course: Big History Project > Unit 4

ACTIVITY: Infographic — Chemical Abundances: Earth’s Crust

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