Eons Quiz Study Guide

Precambrian 3 divisions? Based on Radiometric dates

• Protozoic Eon (542 my - 2.5 by) youngest

• Archean Eon (4.0 by - 2.5 by) oldest

• Hadean Eon (4.6 by - 4.0 by) formation of Earth

Hadean Formation

• No rock record during this time, only at the end when Zircon crystals started forming

• Meteorite bombardment, volcanism, extreme temperatures

• A sea of magma covered much of the Earth’s surface

• An early atmosphere started to form

Komatiite - what forms it?

• Only formed during Early Earth when the temperatures were extreme.

• Lots of heat is needed to form Komatiite

Archean tectonics overview

• Small continent mass

• Plate tectonic movement was rapid

• Passive continental Margins

• Occurs where the transition from land to sea such as a divergent boundary

Archean atmosphere

• Formed by outgassing

• No free oxygen at first

• Oxygen began to appear

• Photochemical dissociation of H2O by UV radiation

• Photosynthesis

• Oceans began to accumulate

Evidence of oxygen present

• Banded Iron Formation: BIFs

• Made of hematite layered with Fe-rich chert. The hematite is FE2O3. In the presence of free O2 in the atmosphere the Fe would oxidize before forming this mineral.

First supercontinent in Proterozoic

• Gonawanaland formed

• Consists of southern continents.

• Luarentia and Gondawanaland formed a supercontinent known as Rodinia at the end of Proterozoic Eon

Rock evidence in Proterozoic

• Banded Iron Formations (BIFs) – Reflect increasing oxygen levels.

• Glacial Tillite – Evidence for early ice ages, such as the Snowball Earth.

• Sedimentary – Show evidence of more stable continental environments. (

Stromatolites

• Produce O2

• BIFs became common 2.5 - 2.0 by

• Continental red beds appeared 1.8 by

• Atmosphere oxidizing

• First oxygen in aquatic areas then in the atmosphere

First multicellular organism

• It may have developed from specialized colonies

• Ediacaran

• Soft-bodied, Nearshore, shallow marine

• 670 - 570 my