UNIT 1 SES 1 A AND B How

UNIT 1 SES 1 – A AND B How Early Earth Formed Chapter 22 Page 618

Section 22. 1 Early Earth Early earth is estimated to be 4. 56 Billion Years Old! How do we know this? We have several things to base this on…

#1 ROCK EVIDENCE Zircon minerals found in rocks date back 4. 7 Billion years ago. Therefore we can assume the rocks are at least that old!

#2. Solar System Evidence Meteorites that constantly land on earth are between 4. 7 and 4. 5 Billion years old. and, moon rocks collected are 4. 7 Billion years old

Early earth – it’s Heat Sources From one of three things: 1. Gravitational Contraction 2. Radioactivity 3. Bombardment

Gravitational Contraction #1 Possibly formed from accumulation of rocky bodies orbiting the sun. It then grew bigger and increased gravity This caused it to squeeze and increase pressure causing the temp to rise!

#2 � Radioactivity Earth had/has radioactive isotopes that release heat

Bombardment � Asteroids, meteors, and other things impacted earth creating great thermal energy!

Now Earth cools… � � � Earth began to cool enough to allow an atmosphere and ocean to form eventually. When? We’re not sure, but maybe water formed in it’s first 200 million years. Earth is still cooling…

22. 2 Formation of the Crust and continents came first! � We believe that the molten hot earth began to cool – forming a crust and the minerals and elements began to separate internally by density! � Ex – pudding “skin” ewwwww!

22. 3 Formation of the atmosphere and oceans � Possibly from meteors, etc hitting earth contained water which vaporized upon impact – creating an atmosphere. � Once volcanoes began to erupt, they too released gases that helped create the atmosphere. This created storms which accumulated surface water – oceans, lakes, etc. �

Formation of Oceans � � Water vapor in the atmosphere accumulated and began to fall back to earth. This rain began to fall down the mountains and dissolve the surface minerals which accumulated as oceans making them salty!

Hadean No evidence found directly! � But…zircon minerals found in metamorphic Australian rocks. Believed to be 4. 4 Billion years old! �

Archean � Earliest Organisms (living things) found! � Unicellular orgs.

Proterozoic � Multicellular organisms found