[meteorite-list] Earth Life 'May Have Come From Mars'

[Ron Baalke]

http://www.bbc.co.uk/news/science-environment-23872765

Earth Life 'May Have Come From Mars'
By Simon Redfern 
BBC News
August 28, 2013

Life may have started on Mars before arriving on Earth, a major scientific 
conference has heard.

New research supports an idea that the Red Planet was a better place to 
kick-start biology billions of years ago than the early Earth was.

The evidence is based on how the first molecules necessary for life were 
assembled.
 
Details of the theory were outlined by Prof Steven Benner at the Goldschmidt 
Meeting in Florence, Italy.

Scientists have long wondered how atoms first came together to make up 
the three crucial molecular components of living organisms: RNA, DNA and 
proteins.

The molecules that combined to form genetic material are far more complex 
than the primordial "pre-biotic" soup of organic (carbon-based) chemicals 
thought to have existed on the Earth more than three billion years ago, 
and RNA (ribonucleic acid) is thought to have been the first of them to 
appear.

Simply adding energy such as heat or light to the more basic organic molecules 
in the "soup" does not generate RNA. Instead, it generates tar.

RNA needs to be coaxed into shape by "templating" atoms at the crystalline 
surfaces of minerals.

The minerals most effective at templating RNA would have dissolved in 
the oceans of the early Earth, but would have been more abundant on Mars, 
according to Prof Benner.

Red or dead

This could suggest that life started on the Red Planet before being transported 
to Earth on meteorites, argues Prof Benner, of the Westheimer Institute 
of Science and Technology in Gainesville, US.

The idea that life originated on Mars and was then transported to our 
planet has been mooted before. But Prof Benner's ideas add another twist 
to the theory of a Martian origin for the terrestrial biosphere.

Here in Florence, Prof Benner presented results that suggest minerals 
containing the elements boron and molybdenum are key in assembling atoms 
into life-forming molecules.

The researcher points out that boron minerals help carbohydrate rings 
to form from pre-biotic chemicals, and then molybdenum takes that intermediate 
molecule and rearranges it to form ribose, and hence RNA.

This raises problems for how life began on Earth, since the early Earth 
is thought to have been unsuitable for the formation of the necessary 
boron and molybdenum minerals.

It is thought that the boron minerals needed to form RNA from pre-biotic 
soups were not available on early Earth in sufficient quantity, and the 
molybdenum minerals were not available in the correct chemical form.

Prof Benner explained: "It's only when molybdenum becomes highly oxidised 
that it is able to influence how early life formed.

"This form of molybdenum couldn't have been available on Earth at the 
time life first began, because three billion years ago, the surface of 
the Earth had very little oxygen, but Mars did.

"It's yet another piece of evidence which makes it more likely life came 
to Earth on a Martian meteorite, rather than starting on this planet."

Early Mars is also thought to have had a drier environment, and this is 
also crucial to its favourable location for life's origins.

"What's quite clear is that boron, as an element, is quite scarce in Earth's 
crust," Prof Benner told BBC News, "but Mars has been drier than Earth 
and more oxidising, so if Earth is not suitable for the chemistry, Mars 
might be.

"The evidence seems to be building that we are actually all Martians; 
that life started on Mars and came to Earth on a rock," he commented.

"It's lucky that we ended up here, nevertheless - as certainly Earth has 
been the better of the two planets for sustaining life. If our hypothetical 
Martian ancestors had remained on Mars, there may not have been a story 
to tell."