Chapter 22 - Earth Space Science
Define LAURENTIA
LAURENTIA: ancient continent formed during the Proterozoic that is the core of modern day North America
Define METEORITE
METEORITE: a small fragment of an orbiting body that has fallen to Earth generating heat; does not completely burn up in Earth's atmosphere and strikes Earth's surface, sometimes leading to an impact crater
Define MICROCONTINENT
MICROCONTINENT: a small fragment of granite-rich crust formed during the Archean
Explain Radioactivity and how it effected Earth
RADIOACTIVITY: Scientists know that certain radioactive isotopes were more abundant in Earth's past than they are today. While some isotopes are longer lasting, and continue to decay today, others were short-lived and have nearly disappeared. Radioactive decay generates heat. Because there were more radioactive isotopes in early Earth, more heat was generated making Earth hotter than it is today.
Describe the Mountain Building process. What are mountain building episodes called?
So during the Proterozoic, microcontinents that formed during the Archean collided with each other, becoming larger but fewer in number. As they collided they formed massive mountains - mountain building episodes called Orogenies.
Define ASTEROID
ASTEROID: metallic or silica-rich object 1 km-950 km in diameter that bombarded early Earth generating heat energy; rocky remnant of early solar system found mostly between orbits of Mars & Jupiter in the asteroid belt
List the Time Line of Earth.
- 4.6 bya = Rocks of oldest meteorites form - 4.56 bya = Earth forms - 4.6-3.9 bya = Heavy bombardment of Earth by asteroids and meteorites occurs - 4.45 bya - Oldest moon rocks form - 4.4 bya = oldest dated zircon from granite crust forms - 3.9-3.5 bya = first living things appear - 3.5 bya = oldest known cyanobacteria appear - 3.5 bya = oldest known stromatolites appear - 3.0-1.8 bya = stromatolites increase local oxygen levels - 2.5 bya = formation of most granite continental cores is completed - 2.1 bya = oldest known eukaryotes appear - 1.8-1.6 bya = volcanic island arc collides with Laurentia - 1.2-1.0 bya = grenville orogeny occurs - 750 mya = widespread glaciation occurs - 630 mya = first undisputed multicellular organisms appear - 630-540 mya = ediacaran fauna flourish - 542 mya = Proterozoic ends
List the 3 heat sources of Earth shortly after it formed
3 heat sources of Earth shortly after it formed: 1. gravitational contraction 2. radio activity 3. Bombardment by asteroids & meteorites
List 4 important developments of Earth by the end of the Proterozoic
4 important developments of Earth by the end of the Proterozoic: 1. formation of 75% of present day North America 2. formation of all the major masses of continental lithosphere 3. Formation of first super continent, Rodinia 4. formation of an atmosphere & ocean had formed
Explain the Evidence of Crustal Rock. How did it form? What do they prove?
Absolute-age dating revealed the oldest crustal rocks are b/w 3.96 - 3.8 billion years old. Evidence that Earth is more than 3.96 billion years old exists in small grains of mineral zircon found in certain metamorphosed Precambrian rocks in Australia. Because zircon is a stable and common mineral that can survive erosion and metaphosphorism, scientists often use it to age-date old rocks. Geologists theorize that the zircon n Australian rocks is residue from crustal rocks that no longer exist since radiometric dating reveals that the zircon is at least 4.4 billion years old - thus Earth has to be at least this old.
Explain how Coontinental Crust formed and what this led to the formation of.
As the early rustle piece were returned to the mantle, they carried water and the introduction of water into the mantle was essential for the formation of the first continental crust. BECAUSE the water reacted with the mantle material to produce new material that was less dense than the original crustal pieces. As the new material reemerged on Earth's surface, it crystallized to form small fragments of granite-containing crust. Granite makes up much of the crust that forms Earth's continents today. Volcanic activity in the Archean contributed to more small fragments of granite-rich crust forming Earth's continents today. These crustal fragments are called microcontinents which were large enough to be considered continents.
Explain the cores of the continents
Continents contain a core of the Archean and Proterozoic rock called a Precambrian Shield. The Precambrian Shield of North America is called the Canadian Shield. It is exposed in parts of Canada, Minnesota, Wisconsin, Michigan, New York and Greenland.
Define CANADIAN SHIELD
CANADIAN SHIELD: name given to the Precambrian Shield in North America b/c much of it is exposed in Canada
Define CRATON
CRATON: continental core formed from Archean or Proterozoic microcontinents - deepest (as far as 200 km into mantle) & most stable part of continent
Explain DIFFERENTIATION and its association to Earth
DIFFERENTIATION: Earth forming, so Iron sank towards centre because high density materials sink a low density materials rise. And light density materials like silicon and oxygen remained closer to the surface. The process by which a planet becomes internally zones when heavy materials sink towards its centre and lighter materials accumulate toward its surface is called differentiation. Here are the zones: - Inner core - outer core - lower mantle - upper mantle -crust This process explains the relative densities of parts of Earth today - denser elements much less in Earth's crust than it is in entire earth as whole and less dense much more abundant in Earth's crust than it is in entire Earth as whole.
Define DIFFERENTIATION
DIFFERENTIATION: process in which planet becomes internally zones with heavy materials sinking towards the centre & the lighter materials accumulating near its surface
How can we use evidence from the solar system to show how old Earth is?
Evidence from meteorites and other bodies seems to suggest that the Earth is more than 4.4 billion years old since some meteorites that have fallen on Earth have been dated at between 4.7 - 4.5 bya. Since most scientists agree that parts of the solar system formed at the same time, they can assume that Earth and meteorites are approximately the same age. Additionally - the moon rocks are dated back to 4.45 by a and since the moon formed very early in Earth''s history, when a massive solar system body collided with Earth, scientists agree that Earth is about 4.56 bya.
How did ASTEROID AND METEORITE BOMBARDMENT effect Earth temp wise.
For the first 500-700 million years of Earth's history, many moree asteroids were distributed throughout the solar system than there are today and collisions were much more frequent. The impacts of these bodies on Earth's surface generated a tremendous amount of thermal energy. Scientists think that the collision that formed the moon generated so much heat that much of Earth melted. The debris from the impacts also caused a blanketing effect which prevented newly generated heat from escaping to space.
Explain GRAVITATIONAL CONTRACTION
GRAVITATIONAL CONTRACTION: another source of Earth's hear was gravitational contraction. Meteor bombardment and the resulting accumulations of meteorite material caused Earth to become larger. The weight of the material caused gravitational contraction of the layers beneath. This energy was converted into thermal energy. The meteorite's material also caused a blanketing effect, which kept the heat from escaping
Explain Gravitational Contraction and how it effected Earth
GRAVITATIONAL CONTRACTION: scientists think that the Earth formed by the gradual accumulation of small, rocky bodies in orbit around the Sun. As Earth accumulated these small bodies, it grew in size and mass. With increased mass came increased gravity. Gravity caused Earth's centre to squeeze together with so much force that the pressure raised Earth's internal temp.
What is LAURENTIA and how did it form?
One of earth's largest Proterozoic land-masses was Laurentia: the ancient continent of North America. The growth of LAurentia involved many different mountain building events for example between 1.8-1.6 by a, thousands of square kms were added to LAurentia when Laurentia collided with a volcanic island arc. This collision is called the Yava-Mazatzal Orogeny
Define PRECAMBRIAN SHIELD
PRECAMBRIAN SHIELD: the top of a carton exposed at Earth's surface
Describe Pangaea and how it formed
Pangaea was a single landmass containing all of Earth's continents and formed relatively recently in Earth's history - only about 200 mya. The plate tectonic forces that formed Pangea has been at work since the end of the Archean.
Describe what the Precambrian eon was like: how long did it span? What do we know about it? How is our knowledge limited?
The Precambrian, which includes the Hadean, Archean and Proterozoic Eons, is a time period that spans nearly 90% of the Earth's history. When Earth first formed, it was hot, volcanically active and no continents existed on its surface. Rocks of Earth's earliest eon - the Hadean - do not exist, so scientists know very little about Earth's first 700 million years. The oldest existing rocks and earliest signs of life are from the Archean. Earliest signs of life were simple unicellular organisms.
What was the first super continent? How did it form? What was it called? When did the breakup of this super continent begin?
The collision of Laurentia and Amazonia occurred at the end of the Proterozoic about 1.3-1.6bya. This collision coincided with the formation of Earth's first super continent, Rodinia. Rodinia was positions on the equator with Laurentia at its centre. By the time Rodinia formed, nearly 75% of Earth's continental crust was in place. The remaining 25% was added during the 3 eras of the Phanerozoic eon. The breakup of this supercontinent began about 750 mya.
Describe Earth's earliest crust.
The crust was probably similar to the basaltic crust that underlies Earth's oceans today. Present day oceanic crust is recycled at subductive zones. Pieces of Earth's earliest crust were also recycled but we don't know how that recycling process occurred. Some suggest that it occurred by a process that no longer occurs on Earth today - and that the recycling process was so vigorous that none of the Earth's earliest crust exists today.
What will happen to the number of radioactive isotopes as the Earth continues to get older?
The number of radioactive isotopes will decrease
When did Earth cool enough for liquid water to form? Does this process continue? What happened as Earth cooled
Within its first 200 million years. Cooling process continues today. As much as half of Earth's internal heat remains from Earth's formation As earth cooled, the minerals and elements from molten magma became concentrated in specific density zones.
Define ZIRCON
ZIRCON: very stable and common mineral that scientists often use to age-date old rocks
Describe CRATONS.
much of the microcontinents that formed during the Archean and early Proterozoic still exist as the cores of continent's today. A carton which is the oldest and most stable part of a continent is attached to a part of the upper mantle and has a depth that can extend 200 km. Cratons are made up of granitic rocks like granite and gneiss, with alternating bands of metamorphosed basaltic rocks which represent ancient continental collisions. The Archean cartons represent about 10% of Earth's total landmass. Most of the cartoons are buried beneath sedimentary rocks however in some places, deep erosion has exposed rocks of the craton. These exposed area are called th Precambrian Shield and in North America this Shield is called the Canadian Shield because much of it is exposed in Canada. The rocks in this shield are about 3.8 billion years old and in contrast other rocks in North America's platform are younger than 600 million years.
