Why would they think Earth was "seeded" with life? Why not start with
and prove or disprove life originated here? What is the attraction for
scientists of this theory?

Hollow spheres found in a primordial meteorite could yield clues to the
origin of life on Earth.

Scientists say that "bubbles" like those in the Tagish Lake meteorite
may have helped along chemical processes important for the emergence of
life.

The globules could also be older than our Solar System - their
chemistry suggests they formed at about -260C, near "absolute zero".

Details of the work by Nasa scientists are published in the journal
Science.

Analysis of the bubbles shows they arrived on Earth in the meteorite
and are not terrestrial contaminants.

These hollow spheres could have provided a protective envelope for the
raw organic molecules needed for life.

Dr Lindsay Keller of Nasa's Johnson Space Center (JSC) in Houston,
Texas, told BBC News that some scientists believed such structures were
"a step in the right direction" to making a cell wall.

But he emphasised that the globules in Tagish Lake were in no way
equivalent to a cell. The hollow spheres seem to be empty, but they do
have organic molecules on their surfaces.

Mike Zolensky, a Nasa mineralogist, commented: "If, as we suspect, this
type of meteorite has been falling on to Earth throughout its entire
history, then the Earth was seeded with these organic globules at the
same time life was first forming here."

Co-author Keiko Nakamura-Messenger of JSC told BBC News: "We reported
only 26 globules in this paper, because they are small and hard to
analyse. But we have seen hundreds in a small area. We can estimate
that there are billions of them in this meteorite."

The ratios of different forms, or isotopes, of the elements hydrogen
and nitrogen in the meteorite are very unusual, which suggests the
structures did not come from Earth, say the scientists.

"The isotopic ratios in these globules show that they formed at
temperatures of about -260C, near absolute zero," said co-author Scott
Messenger, also from Johnson Space Center.

"The organic molecules most likely originated in the cold molecular
cloud that gave birth to our Solar System, or at the outermost reaches
of the early Solar System."

The Tagish Lake meteorite was collected immediately after its fall over
Canada in 2000. It has been maintained in a frozen state, minimising
the potential for terrestrial contamination.