The Visible Earths
01- Nazca,Cocos,Caribbean
02- Pre-Cambrian
03- Shields of the Earth
04- Shield Re-assembly
05- Volcanic Activity
06- Hinge Faults
07- Himalayas
08- Juan De Fuca, Gorda
09- Ring of Fire
10- Oceans Closed
11- Earthquake Waves
12- Mirror Plates
13- Interior
14- Continent Reflections
15- Earthquake Paths
16- Object in the interior
17- Magnetic Mirror
18- Full Expansion
  Mars
19- Contraction
20- Shield Volcanoes
21- Valles Marineris
22- Entry Point of Mars
  The Gas Giants
23- The Gas Giants
  Asteroids
24- Asteroids
  Mercury
25- Mercury
  Venus
26- Venus' Crust
27- Gravity Anomalies
28- Free-Air Correction
29- Rudimentary America
30- Magma Oceans
31- Full Sequence & Notes

02 - Pre-Cambrian

 

 

In the centres of the continents there are large stable shield areas of rock, the oldest rock on the planet surface. They are the thickest parts of the Earth's crust and date from the Pre-Cambrian period, between 600 million and 4.6 billion years ago ( referred to here as 'original shields' ).

These shields are permanently magnetically striped ( a process which occurs when fresh rock emerges and cools, it's orientation in relation to the magnetic poles recorded in its magnetism: also called paleo-magnetism ).

How these shields move in relation to each other is shown by the positions of the fault lines ( the boundaries between the plates on which these shields lie ) and whether the fault lines are extensional ( creating new crust where the seafloor spreads ) or compressional ( destroying old crust at plate boundaries and subsuming it back into the mantle: also called subduction )

Note: see Plate-Tectonic sub-section ( ptss ) for 'Pre-Cambrian', 'Paleo-Magnetism' and 'Subduction'.

 
Alan Lambert 2010