Lecture 2: Birth of the Earth Flashcards
When did the big bang, formation of solar system and earth happen?
big bang was ~13.7 Ga
solar system and then earth soon after formed ~4.6 Ga
What is happening to the universe as a result of the big bang?
It is still expanding
How do we know the universe is still expanding?
By cross-comparing the redshift and brightness of the light emitted from a distant solar system
What was released in large quantities following the big bang?
Neutrons
What happened to the neutrons that were initially released in the big bang, during the subsequent cooling period?
They decayed to divide up their components (electron and proton) which then immediately formed a hydrogen atom
How was the helium atom produced in the early stages of the solar system?
A hydrogen atom would collide with a neutron
What was the source of energy that allowed for the forming of a helium atom?
The energy released during the big bang allowed the neutron and hydrogen atom to collide despite their opposing charges
Why were helium atoms unable to collide with another neutron to therefore keep the development of new elements progressing?
A helium atom cannot acquire another neutron because that would increase its atomic mass from 4 to 5. 5 is an unstable mass and so it cannot form.
What process allowed the solar system to develop new elements other than hydrogen and helium?
Nuclear Fusion
What is the first step in the nuclear fusion process that forms a star?
Hydrogen and helium atoms collide. This releases a lot of energy but leads to a loss of mass. The energy released fights and then balances out against the gravity created around the collision to create a young star
How does a star develop elements through the nuclear fusion process which are heavier than hydrogen and helium?
Two helium atoms have a greater mass than hydrogen so accumulate in the core of the star. If they collide they can produce heavier elements such as Carbon or Neon.
How is silicone in stars produced in the nuclear fusion process?
The different elements that are created following the helium element collision then collide with each other to produce even heavier elements such as Silicone.
How is the core of the star finalised through the nuclear fusion process?
Silicon atoms collide numerous times at the periphery to eventually produce Iron which is much heavier element and so migrates to the centre of the star
Why are collisions of Iron not possible via nuclear fusion?
Because their collision requires so much energy, which is not provided
What allows elements heavier than Iron to form?
In smaller stars there is a lack of energy which allows neutrons to join on to the heavier elements they have which were produced in the nuclear fusion process of bigger stars. This then marks a return to the original process of element formation which produced helium and hydrogen initially.
How do elements heavier than Iron form in stars?
The accumulation of neutrons on to heavier elements causes their mass to increase marking the creation of a new element
How will a supernova happen?
Once a big star’s energy that it produced via nuclear fusion starts to decline it will be overcome by its gravity. This will cause it to shrink and constrain meaning the energy is concentrated in a much smaller space. Eventually the space will become too small so it will explode outwards as a supernova.
What does a supernova explosion allow to happen which is important for the development of the solar system?
The elements that are contained within that star are distributed across a greater area of space and are allowed to collide with each other thereby forming new elements. The agglomeration of these elements in new spaces allows planets to form across space.
Describe the distribution of elements released from a supernova explosion across space
Non-uniform: some places experience a high concentration of the elements while others experience low concentrations
What is the formation process called for new planets?
Rocky planet formation
What happens to a collection of high concentration elements in a part of space?
They essentially coagulate and cluster to form centimetre then kilometre size particles.
What is the name given to the kilometre-size ‘particles’ of elements that clustered together?
Planetesimals
What happens to Planetesimals once they start to grow roughly 1000km in size?
The growth/accumulation rate starts to increase
What allows the growth/accumulation rate of planetesimals to increase once they reach the 1000km scale?
they have a bigger surface area which means they can be involved in more collisions, but also their size means they have a bigger gravitational pull which draws more elements toward them to collide
How long does the process of planetismals growing to 1000km scale size take?
tens to hundreds of thousands of years
What is the name given to the element accumulation positive feedback?
Runaway accretion
What happens to planetesimals on million-year time scales?
They collide with each other
What is the name given to the product of a collision between wo planetesimals?
Oligarch/Planetary embryo
What happens to planetesimals, which are now called oligarchs, on billion-year time scales?
They will form between two to five earth-size planets
What is mars regarded as in terms of planetary evolution?
A failed planet because it did not reach the size expected through this process
What happens to planets that form further away from the sun?
They will experience cooler temperatures which means some gases solidify and add to the planet’s outer layers
Describe the relationship between element density and depth in planet structure
Denser elements are found at the core of the planets while lighter elements are located at the outer edges
Where would we find Iron?
The inner core
Where would we find Silicone and oxygen?
Outer layer and crust
What sort of elements are also found at the outer core of the planets and why?
Elements that are important for life such as phosphorus and potassium
What happens to solidity as you move away from the core and why?
Declines because there is less compaction
Why are some elements found completely separate from each other in the planet structures?
Because they do not mix well in terms of denisty
