8barcheahist - Archean Remember Precambrian time includes...

Info icon This preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Archean Remember… Precambrian time includes 80% of the earth's history, from 4.5 byr - 700 myr. So for the first 500 myr there is no geologic record. Original crust was thin and composed mainly of komatite & basalt. Granites have formed from basalts from partial melting with the crust. – -mafic to felsic This process causes enrichment of lighter elements such as Si, Al, K, Na. Granites formed by accreted terrains onto a larger land mass. The chemistry of granitic rocks changed through time. This seems to indicate increasing chemical differentiation of the earth through time. Partial melting Early crust characteristics Early atmosphere
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
2 How did the oxygen get into the atmosphere? Photochemical dissociation – Breakup of water molecules by ultraviolet light. Also produces ozone. – Significant in the past. • Photosynthesis – More important. Plants evolved to split carbon dioxide into carbon and oxygen.
Image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern