Lecture 2: Birth of the Earth

Question 1

When did the big bang, formation of solar system and earth happen?

Answer 1

big bang was ~13.7 Ga

solar system and then earth soon after formed ~4.6 Ga

Question 2

What is happening to the universe as a result of the big bang?

Answer 2

It is still expanding

Question 3

How do we know the universe is still expanding?

Answer 3

By cross-comparing the redshift and brightness of the light emitted from a distant solar system

Question 4

What was released in large quantities following the big bang?

Answer 4

Neutrons

Question 5

What happened to the neutrons that were initially released in the big bang, during the subsequent cooling period?

Answer 5

They decayed to divide up their components (electron and proton) which then immediately formed a hydrogen atom

Question 6

How was the helium atom produced in the early stages of the solar system?

Answer 6

A hydrogen atom would collide with a neutron

Question 7

What was the source of energy that allowed for the forming of a helium atom?

Answer 7

The energy released during the big bang allowed the neutron and hydrogen atom to collide despite their opposing charges

Question 8

Why were helium atoms unable to collide with another neutron to therefore keep the development of new elements progressing?

Answer 8

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.

Question 9

What process allowed the solar system to develop new elements other than hydrogen and helium?

Answer 9

Nuclear Fusion

Question 10

What is the first step in the nuclear fusion process that forms a star?

Answer 10

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

Question 11

How does a star develop elements through the nuclear fusion process which are heavier than hydrogen and helium?

Answer 11

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.

Question 12

How is silicone in stars produced in the nuclear fusion process?

Answer 12

The different elements that are created following the helium element collision then collide with each other to produce even heavier elements such as Silicone.

Question 13

How is the core of the star finalised through the nuclear fusion process?

Answer 13

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

Question 14

Why are collisions of Iron not possible via nuclear fusion?

Answer 14

Because their collision requires so much energy, which is not provided

Question 15

What allows elements heavier than Iron to form?

Answer 15

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.

Question 16

How do elements heavier than Iron form in stars?

Answer 16

The accumulation of neutrons on to heavier elements causes their mass to increase marking the creation of a new element

Question 17

How will a supernova happen?

Answer 17

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.

Question 18

What does a supernova explosion allow to happen which is important for the development of the solar system?

Answer 18

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.

Question 19

Describe the distribution of elements released from a supernova explosion across space

Answer 19

Non-uniform: some places experience a high concentration of the elements while others experience low concentrations

Question 20

What is the formation process called for new planets?

Answer 20

Rocky planet formation

Question 21

What happens to a collection of high concentration elements in a part of space?

Answer 21

They essentially coagulate and cluster to form centimetre then kilometre size particles.

Question 22

What is the name given to the kilometre-size ‘particles’ of elements that clustered together?

Answer 22

Planetesimals

Question 23

What happens to Planetesimals once they start to grow roughly 1000km in size?

Answer 23

The growth/accumulation rate starts to increase

Question 24

What allows the growth/accumulation rate of planetesimals to increase once they reach the 1000km scale?

Answer 24

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

Question 25

How long does the process of planetismals growing to 1000km scale size take?

Answer 25

tens to hundreds of thousands of years

Question 26

What is the name given to the element accumulation positive feedback?

Answer 26

Runaway accretion

Question 27

What happens to planetesimals on million-year time scales?

Answer 27

They collide with each other

Question 28

What is the name given to the product of a collision between wo planetesimals?

Answer 28

Oligarch/Planetary embryo

Question 29

What happens to planetesimals, which are now called oligarchs, on billion-year time scales?

Answer 29

They will form between two to five earth-size planets

Question 30

What is mars regarded as in terms of planetary evolution?

Answer 30

A failed planet because it did not reach the size expected through this process

Question 31

What happens to planets that form further away from the sun?

Answer 31

They will experience cooler temperatures which means some gases solidify and add to the planet’s outer layers

Question 32

Describe the relationship between element density and depth in planet structure

Answer 32

Denser elements are found at the core of the planets while lighter elements are located at the outer edges

Question 33

Where would we find Iron?

Answer 33

The inner core

Question 34

Where would we find Silicone and oxygen?

Answer 34

Outer layer and crust

Question 35

What sort of elements are also found at the outer core of the planets and why?

Answer 35

Elements that are important for life such as phosphorus and potassium

Question 36

What happens to solidity as you move away from the core and why?

Answer 36

Declines because there is less compaction

Question 37

Why are some elements found completely separate from each other in the planet structures?

Answer 37

Because they do not mix well in terms of denisty