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Posted in response to What era does silica appear in geological earth from Laura on May 22, 2007 at 17:51:47:

Re: What era does silica appear in geological earth

Hello Laura;

I have not read the article to which you referred, but let me try to answer your questions.

From your post, my guess is that the "silica" to which they refer is quartz sand, or was sand. Sand usually, but not always, requires water for its formation. Water is the chief agent for weathering quartz out of igneous rock and grinding it to sand.
The sand of course can then lithify to make sandstone or, with pebbles, conglomerate.

As for when "silica" appeared in/on earth, since the beginning. Early on, it separated and crystallized from the magma as quartz when the early continental granite cratons formed. But, silica isn't just quartz. The silicon/oxygen tetrahedron is part of the structure of all silicates.

I am guessing that the news article was reporting that quartz sand silica was more evidence for water on Mars. That would make a lot of sense.

I hope this helps.

Don

From Don Peck - May 23, 2007 at 10:34:38
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