P1 - The Earth in the Universe

Big Bang• 14 thousand million years ago• Theory was proposed by the Catholic Priest George Lemaitre

The solar system was

formed from clouds of gases and

dust in space about

5 thousand million years

ago

The Earth must be older than its oldest rocks which are about

4 thousand million years old

The Sun is a Star• The Sun is a star in the Milky Way galaxy• All stars have a life cycle• There are thousands of millions of galaxies, each

containing thousands of millions of stars, and that all of these make up the Universe

Fusion• Fusion of hydrogen nuclei is the source of the Sun’s energy• All chemical elements larger than helium were made in earlier

stars

1. Milky Way Galaxy:– 100 000 light years– Spins around a black hole

2. Sun: – 1.4 million km– Centre of Solar system

3. Planet: – 120 000km– Orbits sun

4. Moons: – 3500km– Orbits Planets

5. Asteroids: – 1000km– Orbits Sun (between Mars and

Jupiter)6. Comets:

– 3km– Orbits Sun

Diameters and MotionBiggest > Smallest

• Information about distant stars and galaxies comes only from the radiation astronomers can detect

• Light pollution interferes with observations of the night sky

How we know about the Universe

Speed of Light• Light travels at 300 000 km/s • The speed of light means distant objects are observed

as younger than they are now• Light-year = the distance travelled by light in a year

Parallax or Relative Brightness• Can be used to measure the distance to stars• The difficulty of observations makes the distance of stars and

galaxies uncertain

Hubble’s Law• All Galaxies are moving away from us. • The further away the galaxy, the quicker it is moving.• This suggests that the universe is expanding

Future of the Universe

• Understand why the ultimate fate of the Universe is difficult to predict.

Aliens• Astronomers have detected planets around nearby stars • Even if a small proportion of stars have planets, many

scientists think that it is likely that life exists elsewhere in the Universe

• No evidence of alien life has so far been detected

Asteroid Collisions• The frequency of a 15km asteroid hitting Earth is 1 in every 65 million years. • The last one was in Mexico, 65 million years ago. Evidence indicates that this led to the extinction of the dinosaurs

• Be able to label the Core, Mantle, Crust

Structure of the Earth

Theory of Continental Drift• Proposed by Alfred

Wegener • The movement of the

Earth's continents • Evidence for it:

1. Geometric fit of continents

2. Matching fossils 3. Matching mountain

chains 4. Matching rocks

• Reasons for the rejection of Wegener’s theory by geologists of his time:1. Movement of continents not detectable2. Wegener was an outsider to the community of

geologists3. Too big an idea from limited evidence4. Simpler explanations of the same evidence

Seafloor Spreading1. A consequence of movement of the solid mantle2. Seafloors spread by about 10 cm a year3. Produces a pattern in the magnetism recorded in

ocean floors, due to reversals of the Earth’s magnetic field and solidification of molten magma at oceanic ridges.

Tectonic Plates

The following occur at plate boundaries:1. Volcanoes: Plates moving apart2. Mountains: Plates move towards one another. One plate dives underneath

another3. Earthquakes: Plate slide past one another

– Rock processes seen today explain past changes– Continents would be worn down to sea level, if mountains were

not being continuously formed. Therefore the above are an important part of the rock cycle

Rocks provide evidence for changes in the Earth

• Erosion, sedimentation, fossils, folding, radioactive dating, craters.

Actions that Public Authorities can take to Reduce Damage caused by Geo-Hazards

1. Enforce building regulations to limit the effect of earthquakes

2. provide education and training3. monitor natural hazards in the local area to look for early

signs of earthquakes or volcanic activity4. take part in international research

Data• Data statements tell you facts, and may

contain measurements. For example, look at these three statements:– Asteroids are small objects orbiting the Sun – Some asteroids have orbits close to the Earth– The dinosaurs died out at about the same time as

a large crater was made in Mexico

Explanations• Explanations seek to explain the data, and

formulating an explanation requires imagination and creativity.

• One explanation is that an asteroid collision may have killed off the dinosaurs. The asteroid impact would have created dust which blocked out the Sun.

Predictions• A good explanation will explain data, and link

together things which were not thought to be related. It should also make predictions.– Asteroids often contain the rare metal iridium -

data– A huge asteroid impact would send iridium dust

throughout the world - prediction– Sedimentary rocks from the time the dinosaurs

died out contain iridium - data– When the asteroid crashed, the iridium came

from the dust which blocked out the Sun - explanation

Observations• Data and predictions can be used to test an

explanation, but you have to be careful. When an observation agrees with the prediction, it makes you more confident in the explanation, but it does not prove that the explanation is true.

• The opposite is also correct. When an observation disagrees with a prediction, it makes you less confident in the explanation, but it does not prove that the explanation is wrong. The data may be faulty.

Other Theories• The asteroid theory is not the only theory

about the death of the dinosaurs. – There were huge volcanic eruptions in India at the

time the dinosaurs died out (data)– Big volcanic eruptions cause dust clouds which

block out the Sun (data)– The big Indian eruptions could have killed out the

dinosaurs by cooling the Earth (explanation)

Publishing and Peer Review

• Scientists report their ideas to the scientific community, which is made up of all the other scientists. They present them at conferences and then write them up in journals or books.

• At conferences, other scientists will listen and debate the new ideas. Before journals or books are published, other expert scientists read the new ideas and decide if they are sensible. This is called peer review.

Repeating Experiments• Scientists do not usually

accept the results of experiments until someone else has repeated the experiment to get the same results.

• It is hard to set up experiments in geology and astronomy, so new theories here need support from different observations

Different Explanations• Data often allows more than one possible

explanation, so different scientists can have different explanations for the same observations.– Wegener’s ideas could certainly explain similar fossils

in different continents, but other geologists thought that there were once ‘land bridges’ between continents, allowing animals to travel between them.

• The different backgrounds of different scientists can affect their judgements, so they may have quite different explanations for the same data.

New Explanation Become Accepted• A scientific explanation is rarely abandoned just

because some data does not correspond to it. It is safer to stick with a theory that has worked well in the past.– Old geological theory - mountains as wrinkles made by

the Earth shrinking as it cools down.– No clear explanation how continents could move about.– In the 1950s, evidence from magnetism in the ocean

floor showed that the seafloors were spreading by a few centimetres each year. This showed movement of large parts of the Earth’s crust, now called tectonic plates.