What was the Earth like over 4 billion years ago
- 90% was covered in iron-rich ocean
- > there was a co2 atmosphere
- > and the temperature was over 93 degrees celcius
- the Earth was molten to hundreds of km of depth
- > referred to as the magma ocean
State the six steps in the geologic history of the Earth
1) Formation of Earth, 4.6 billion years ago
2) Impacts dominate earliest history
3) Nickel-iron separates and sinks; low-density melts rise to surface
4) Early crust becomes unstable
5) Continents assemble, break up and disperse
6) Today. there is plate tectonism, deep subduction, and buoyant continents that dominate the crust
Describe the characteristics of the Earth during the Hadean Eon from 4.6 billion to 3.8 billion years ago
- conditions were hellish
- there was accretion of millions of planetesimals in a short time
- > planetisimals are the 100 km scale objects that are like the building blocks of other planets in the solar system
- the planet was hot
- > differentiation of iron to core, silicates to mantle and gases to atmosphere
- > there was also a magma ocean
- moon-forming event
- > formed by a Giant Impact
- there was heavy bombardment
Describe the characteristics of the Earth during the Archean Eon 3.8 billion to 2.5 billion years ago
- there is a formation of continental nuclei and assembly of shields(larger continents from older crust)
- > from 3.0 to 2.5 billion years ago
- > biggest fundamental change in the atmosphere was 2.5 billion years ago
- there were few multicellular organisms at this time
- > the main advance in life was cyanobacteria being able to use sunlight to do photosynthesis and use carbon dioxide that was rich in the atmosphere
- > thus they gave off oxygen, which came to be known as th eprimitive oxygen back then
Describe the characteristics of the Earth during the Proterozoic Eon from 2.5 billion to 0.6 billion years ago
- Proto-life
- there is stabilization of continents
- > sedimentary platforms
- > stronger, thicker lithisphere
- > more modern plate tectonics
-there is removal of carbon dioxide from the atmpshere
- increase of oxygen
- > banded iron formation
- > this means that all iron originally dissolved in the oceans was precipitated out because the conditions of the atmosphere changed so much
Describe the Phanarozoic Era characteristics on the Earth(note this eon was from 0.6 billion ears ago to the present)
- there is now evident life
- deposition of sedimentary rocks on continent
- extensive expansion of life in oceans, onto land
- grouping of plates into Pangea and breakup
- also glaciation
- > evidence of glaciation in both phanerozoic and protozoic
- > but more important for the phanerozoic eon
What is a galaxy and a galaxy supercluster
Galaxy
->is a collection of a few hundred million to trillion stars
Galaxy supercluster
->tightly packed chains and sheets of galaxies
How do elements on the Earth form
- they have all formed through nuclear fusion on the stars
- > fusion is the combination of two or more nuclei to form a different, heavier, element
- > the by-product is radiation(including light and heat that we require to live)
Why is the Sun able to undergo fusion
-because it is so large
What is the most abundant element in the universe
- hydrogen is the most abundant element in the universe
- > need 10 million K temperature to get hydrogen burning
- > two hydrogens make deuterium
- > deuterium + hydrogen makes helium
-need high pressures and high temperatures for hydrogen to come together
What elements can be produced on more massive stars
- there is helium burning to produce carbon
- carbon and helium burning to produce oxygen
- neon, sodium, and even iron can be produced
- our Sun does not produce any element heavier than helium
- > all the other heavier elements come from other previous generation of stars
- > these stars needed to live and die to produce heavier elements(supernova)
What is a supernova
- the cataclysmic explosion of a star
- > as a result of internal nuclear reactions
- note iron does not burn
- > so when the star gets to the iron section
- > the star begins to contract and breakdown as it cannot breakdown iron
- > outer shells of unburned fuel reacts suddenly
- > star explodes, spreading elements into space
What is a nebula
- it is a dusty, dense(1000 gas molecules/ 10 cm cube) cloud
- > in space, there is an average of 1 molecule of gas/10 cm cube
- > in Earth’s atmosphere, there is 10^20 gas molecules per 10 cm cube
What is gravitational collapse
- when molecules are concentrated
- > attracted to each other
- > may be triggered by a nearby supernova
Are all planets in our solar system in the plane and orbit in the same direction
-yes
What are T tauri stars
- stars that are similar in mass to the Sun
- >but only about 1 million years old
What are proplyds
- they are disks of dust and gas around young stars
- > contraction of protoplanetary disks
-proplyds can eventuallly become their own planetary system
Describe the stellar nursery in the Orion Nebulla
- there are over 150 proplyds within this region
- > there are stars inside that are very new
- > eg; 2.5 light years across
-since there are so many new stars, the stellar nursery is the place where stars are forming
Describe the steps leading up to accretion, starting out with the formation of a nebula
1) Slowly rotating portion of a large nebula becomes a distinct globule as a mostly gaseous cloud collapses by gravitational attraction
- >this is due to a supernova nearby
2) Rotation of the cloud prevents collapse of the equatorial disk while a dense central mass forms
- >this central mass is the protostar
3) A protostar ignites(1 million years after the collapse of the nebula) and warms the inner part of the nebula
- >vaporizing preexisting dust
- >as the nebula cools, condensation produces solid grains that settle to the central plane of the nebula
- this is the T-tauri stage because it has bipolar outflows
- >the inner part of the nebula is very hot
- >starts to bring material into the disk(accretion)
4) The dusty nebula clears
- >either by dust aggregation into larger particles(planets or planetesimals)
- >or by ejection during a T-tauri stage of the star’s evolution
- a star energized by fusion and a system of cold bodies remains
- >gravitational accretion of these small bodies eventually leads to the development of a small number of small planets
-note all the dust and gas is cleared 10 million years after collapse
Describe the differences in refractory vs volatile substances that result from the collapse of the nebula
refractory
->materials that form solids at very high temperatures
volatile
->materials that condense/solidify at very low temperatures
