Stable Earth – Revision Pack (P1)
Earthquake Waves:
A seismograph shows the different types of waves; there are three types. The first of
which are ‘L waves’ which travel around the surface of the earth very slowly. The
other two are described in the table below:
P waves (longitudinal pressure waves)
- Travel through earth at between
5km/s and 8km/s
- Can pass through solids and
liquids
S waves (transverse waves)
- Travel through earth at between
3km/s and 5.5km/s
- Can ONLY pass through solids
Inside the Earth:
P waves travel right through
the earth and are refracted by
the core – the path taken by P
waves has enabled scientists
to predict the size of the
earth’s core.
S waves are NOT noticed on
the opposite side of earth to
an earthquake. We know that
they cannot travel through
liquids, so this allows us to infer
that the earth’s core is liquid.
Tan or Burn?
P waves travel faster than S
waves.
A tan is caused by the action of ultraviolet (UV) light on the skin. The skin cells
produce melanin which is a pigment which produces a tan.
Those with darker skin will not tan as easily as the UV radiation is filtered out. The UV
radiation is absorbed by the upper layers of their skin so less radiation reaches
underlying skin.
There are many risks associated with extended sun
exposure; these include skin cancer, sunburn and eye
cataracts. To avoid these risks you should wear a high
SPF. You can work out how much time you are
supposed to spend in the sun using this general
formula:
Longest allowed time = SPF x published burn time
People are becoming increasingly aware of the
affects of exposure to UV radiation, including the use
of sun beds.
Stable Earth – Revision Pack (P1)
Depletion of the Ozone
Originally, scientists thought their equipment was poor when they discovered that
the ozone was thinning. However, other scientists confirmed the results and this
boosted confidence in the results.
The ozone is found in the stratosphere which extends to about 50km above the
earth’s surface. The ozone’s job is to filter out UV radiation which is linked to skin
cancer.
CFC gases from aerosols and old refrigerators destroy the ozone and reduce the
thickness of the ozone layer, thus increasing the potential dangers of UV radiation to
humans. It is for this reason that there is an international agreement to reduce CFC
emissions.
The thinnest part of the ozone is just above the
South Pole – this is because the CFC depleting
chemicals work best in colder conditions like
the one above that area.
Scientists are constantly closely monitoring the
thickness of the ozone using satellites.
Stable Earth – Revision Pack (P1)
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