2.1 Solar nebular model

Question 1

When was the Big Bang?

Answer 1

14 billion years ago (14 Ga)

Question 2

When was the solar system formed?

Answer 2

4.6 billion years ago (4.6 Ga)

Question 3

What is a nebula?

Answer 3

A giant cloud of molecular hydrogen and dust.

Question 4

What happened to the nebula to begin the creation of the solar system?

Answer 4

It collapsed, possibly due to the shockwave from a nearby exploding star) and became denser.

Question 5

What is a protoplanetary disc?

Answer 5

A rotating flat gaseous cloud that was created due to the collapse of the solar nebula.

Question 6

What occurred as a result of the heat and high density occurring at the centre of the protoplanetary disc?

Answer 6

It triggered nuclear fusion, increasing the temperature of the surface of the star at the centre of the protoplanetary disc.

Question 7

What is meant by the term accretion?

Answer 7

An increase in mass by the addition of material e.g. by rocky particles colliding.

Question 8

What is a planetesimal?

Answer 8

A small body of rocky material that has been created by gravitational and electrostatic forces. They are around 1 km in diameter.

Question 9

What is a protoplanet?

Answer 9

It forms when planetesimals accrete (join together). They are approximately the size of the moon.

Question 10

Approximately how long did it take for protoplanets to collide and form the terrestrial planets?

Answer 10

Up to 1 billion years.

Question 11

Why did giant gas planets form in the outer reaches of the solar system?

Answer 11

They formed from the less dense elements that was sent further away from the sun when it collapsed and produced a shockwave.

Question 12

What are asteroids?

Answer 12

The left over planetesimals that did not form planets.

Question 13

What are meteorites?

Answer 13

Fragments of asteroids.

Question 14

How did the moon form?

Answer 14

A protoplanet impacted the young Earth between 30 and 50 million years after the formation of the Solar System.

Question 15

What assumption do we have to make in order to use meteorites as evidence for the Earth’s composition and structure?

Answer 15

All the material in the Solar System originated from the same source.

Question 16

What feature do meteorites have that means that can be used as a record of planet formation?

Answer 16

The have remained unaltered since they were formed.

Question 17

What is the evidence for the solar nebular hypothesis?

Answer 17

1. The rocky planets are closest to the Sun and the gas giants further away
2. Most solar system objects orbit and rotate in an organised fashion

Question 18

Which type of meteorites represent the Earth’s core?

Answer 18

iron meteorites

Question 19

What are iron meteorites composed of?

Answer 19

an alloy of iron and nickel

Question 20

Which type of meteorites represent the Earth’s mantle?

Answer 20

stony meteorites

Question 21

What are stony meteorites composed of?

Answer 21

silicate mineral including olivine, pyroxene and plagioclase feldspar

Question 22

Which type of meteorite are thought to represent the overall composition of the Earth?

Answer 22

chondrites

Question 23

What are chondrites composed of?

Answer 23

silicate minerals plus water, organic compounds, and chondrules

Question 24

What are chrondules?

Answer 24

originally molten droplets, for example of olivine, which formed at high temperatures in the early solar cloud (found in chondrite meteorites)

Question 25

Which type of meteorite is chemically similar to the Sun, except for the absence of hydrogen and helium?

Answer 25

chondrites

Question 26

State three pieces of evidence for asteroid impact.

Answer 26

• the impact sites are circular and have a rim of broken rock built up of ejected material
• quartz grains may be violently shocked and even melted
• rock strata are tilted
• material at depth is brecciated (broken up)
• the ejected material falls back to the surface in an inverted sequence because material closer to the surface is ejected first and falls back to the surface earlier

Question 27

What is the relationship between the size of an asteroid or meteorite impact and their frequency?

Answer 27

The larger the size of the impact, the less frequent the impacts are (negative correlation).