BBC Knowledge June 2017

6. ‘Old Tjikko’
   Norway spruce
   9,550 years old
   Fulufjället Mountains,
   Sweden
   7. ‘Old Rasmus’
   Norway spruce
   9,500 years old
   Härjedalen,
   Sweden
   8. Antarctic moss
   5,500 years old
   Elephant Island,
   Antarctica
   9. Bristlecone pine
   5,066 years old
   White Mountains,
   California, the USA
   10. ‘Methuselah’
   Bristlecone pine
   4,848 years old
   White Mountains,
   California, the USA

ILLUSTRATIONS: RAJA LOCKEYX

Do all planets have

magnetic fields?

No, not all planets have magnetic fields. The four gas giants have extremely

strong magnetic fields, Earth has a moderately strong magnetic field,

Mercury has an extremely weak field, but Venus and Mars have almost

no measurable fields. Planetary magnetic fields are formed by the interaction

between the convection of interior conducting material (molten rock and

metal) and the planet’s own rotation. Mercury’s field is weak because

it rotates so slowly. Venus doesn’t have an appreciable field because

there appears to be little convection in its molten interior. Mars doesn’t

have an appreciable field – although it did in the past – because

its interior has solidified. AGu

How much sleep do

we really need?

The cliché is that we need eight hours a night, but

the actual answer to this question is more complicated.

Our sleep requirements change throughout life. Guidelines

proposed by the National Sleep Foundation in 2015

recommended that newborns have 14 to 17 hours per

night, teenagers have eight to 10 hours, and adults have

seven to nine hours. These guidelines focus largely on

‘average’ requirements, but individuals can differ greatly

from one another. For example, it may be appropriate for

certain teenagers to have as few as seven hours per night,

or as many as 11. If you’re not functioning your best, it’s

worth considering whether you’re getting enough sleep.AGr

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