Transcript P1 - The Earth in the Universe

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.
2.
3.
4.
5.
6.
Milky Way Galaxy:
– 100 000 light years
– Spins around a black hole
Sun:
– 1.4 million km
– Centre of Solar system
Planet:
– 120 000km
– Orbits sun
Moons:
– 3500km
– Orbits Planets
Asteroids:
– 1000km
– Orbits Sun (between Mars and
Jupiter)
Comets:
– 3km
– Orbits Sun
Diameters and Motion
Biggest > Smallest
How we know about the Universe
• Information about distant stars and galaxies comes only
from the radiation astronomers can detect
• Light pollution interferes with observations of the night sky
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
Structure of the Earth
• Be able to label the Core, Mantle, Crust
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 detectable
2. Wegener was an outsider to the community of
geologists
3. Too big an idea from limited evidence
4. Simpler explanations of the same evidence
Seafloor Spreading
1. A consequence of movement of the solid mantle
2. Seafloors spread by about 10 cm a year
3. 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.
2.
3.
Volcanoes: Plates moving apart
Mountains: Plates move towards one another. One plate dives underneath
another
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 training
3. monitor natural hazards in the local area to look for early
signs of earthquakes or volcanic activity
4. 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.