快猫短视频

THE long-standing mystery about how life came to be left-handed may finally
have been solved.

Many molecules have alternate forms that are mirror images, like our left and
right hands. Yet all life on Earth uses only left-handed amino acids to make
proteins.

It had been suggested that polarised light was to blame, because left
and right-handed molecules absorb polarised light differently. In some reactions
driven by light, this causes one form to break down faster, leaving a larger
proportion of the other. But sources of polarised light in the Universe are rare
(快猫短视频, 27 November 1999, p 20).

Now Geert Rikken and Ernst Raupach of the Grenoble High Magnetic Field
Laboratory in France have shown that unpolarised light in a magnetic field can
have a similar effect to polarised light. They used a molecule called chromium
oxalate, which is broken down by light. 鈥淥ne `handedness鈥� absorbs unpolarised
light in a magnetic field faster than the other, so it falls apart faster,鈥� says
Rikken.

Using magnetic fields of 15 tesla鈥攅quivalent to about 30 fridge
magnets鈥攖hey saw around one extra molecule in a thousand for one hand. The
same mechanism could affect amino acids. 鈥淭he numbers would be different, but
the effect would still work,鈥� says Rikken. Over millions of years it could be
enough to explain why only left-handed amino acids were around when life first
formed. The Earth鈥檚 magnetic field is too weak to have much effect, so he thinks
extraterrestrial magnetic fields might have been responsible.

But astronomer Alain Jorissen of the French-speaking Free University of
Brussels points out that the effect is dependent on the wavelength of the light.
The different components of white light would have different effects. 鈥淭he net
effect would be almost zero.鈥� For all amino acids to end up left-handed, he
says, you would need light of one particular wavelength.