Earth Science Chapter 22.2 Riddle · Earth’s first supercontinent Rodinia Positioned at the...
Transcript of Earth Science Chapter 22.2 Riddle · Earth’s first supercontinent Rodinia Positioned at the...
Earth Science
Chapter 22.2
Riddle
Formation of the Crust Scientists believe that Earth consisted of hot molten
rock.
As the planet cooled minerals and elements became concentrated in specific density zones.
Differentiation Less dense materials float
on top of more dense materials
Iron- most dense- sank Silicon and oxygen- less
dense- floated to surface Differentiation: process by
which a planet becomes internally zoned when heavy materials sink toward the center and lighter materials accumulate near its surface.
Relative Densities
47%
28%
8%
5%
3%3% 3% 2% 1%
Earth’s Crust
Oxygen Silicon Aluminum
Iron Calcium Sodium
Potassium Magnesium All others
33%
31%
15%
2%
1%4% 14%
Entire Earth
Iron Oxygen Silicon Calcium
Aluminum Sulfur Magnesium
Earliest Crust Some type of early crust formed as soon as Earth’s
upper layer began to cool.
Similar to basaltic crust of Earth’s oceans
Early crust was recycled
Today it is recycled in subduction zones
Early recycling was vigorous
This vigorous recycling is not a process on Earth today
Continental Crust Early crustal pieces contained water.
This water was necessary for forming continental crust
Water reacted with mantle material to produce new less dense material.
This material crystallized to form small granite
Granite makes up most of the continental crust
These crustal fragments are called microcontinents
Microcontinents are not large enough to be considered continents.
Cratons Cratons- the oldest and most
stable part of a continent Most microcontinents formed
during the Archean and early Proterozoic still exist at the cores of today’s continents.
Cratons are made of granitic rocks Granite Gneiss Alternating bands of
metamorphosed basaltic rocks Represent 10% of Earth’s land
mass
Precambrian Shields Most cratons are buried beneath sedimentary rocks
Some places deep erosion has exposed the rocks of the craton Precambrian shield- the exposed rocks of the craton
Canadian Shield- the North American craton is called the Canadian shield Most of the exposed rock is in Canada
Also occurs in Greenland, northern Minnesota, Wisconsin and Michigan
Contain valuable minerals Nickel, silver and gold
Oldest rocks are about 3.8 billion years old.
Precambrian Shields
Canadian Shield
Growth of the Continents Earth’s continents were
once one big landmass
Pangaea
200 mya
Plate tectonics forces that formed Pangaea have been working since the end of the Archean
Mountain Building During the Proterozoic,
the microcontinents that formed during the Archean began to collide with each other
Formed massive mountains Orogenies-the mountain
building episodes The belts of rocks that are
deformed by the immense energy of the collisions are orogenies
Laurentia One of Earth’s largest
Proterozoic land masses
Laurentia- Ancient continent of
North America
Involved many different mountain-building events
Between 1.8 and 1.6 mya thousands of square kilometers were added
This collision was called Yavapai-Mazatzal Orogeny
First Supercontinent Collision of Laurentia with
Amazonia Occurred at the end of the
Proterozoic about 1.3 to 1 mya Coincided with formation of
Earth’s first supercontinent Rodinia
Positioned at the equator with Laurentia at its center.
By the time Rodinia formed, nearly 75% of Earth’s continental crust was in place.
The remaining 25% was added during the three eras of the Phanerozoic eon
The break up of this supercontinent began about 750 mya.