It covers
more than two-thirds of the Earth’s surface, but the exact origins of
our planet’s water are still something of a mystery. Scientists have
long been uncertain whether water was present at the formation of the
planet or if it arrived later, perhaps carried by comets and meteorites.
In a new paper published on the 13 November in the journal Science,
researchers present compelling new evidence that the former theory is
correct – water has been a fundamental part of Earth since it was formed
from the accretion of dust and rocks more than 4.5 billion years ago.
Researchers
from the Universities of Glasgow and Hawaii describe in their paper how
they used advanced ion microprobe technology to examine a set of rocks
from Baffin Island, in the Canadian territory of Nunavut. The ion
microprobe, housed at the University of Hawaii at Manoa, allowed
researchers to focus on minute pockets of glass inside these
scientifically important rocks, and to detect the tiny amounts of water
within. The ratio of hydrogen to deuterium in the water would provide
them with valuable new clues as to its origins. Hydrogen has an atomic
mass of one, while deuterium, an isotope of hydrogen also known as
'heavy hydrogen', has an atomic mass of two. Scientists have discovered
that water from different types of planetary bodies in our solar system
have distinct hydrogen / deuterium ratios.
Dr Lydia Hallis led the
research, first at the University of Hawaii at Manoa and then as a Marie
Curie Research Fellow at the University of Glasgow. She said: "The
Baffin Island rocks were collected back in 1985, and scientists have had
a lot of time to analyse them in the intervening years. As a result of
their efforts, we know that they contain a component from Earth’s deep
mantle. On their way to the surface, these rocks were never affected by
sedimentary input from crustal rocks, and previous research shows their
source region has remained untouched since the Earth’s formation.
Essentially, they are some of the most primitive rocks we’ve ever found
on the surface of the Earth, and so the water they contain gives us an
invaluable insight into the Earth’s early history and where its water
came from. We found that the water had very little deuterium, which
strongly suggests that it was not carried to the Earth after it had
formed and cooled. Instead, water molecules were likely carried on the
dust that existed in a disk around our Sun before the planets formed.
Over time this water-rich dust was slowly drawn together to form our
planet. Even though a good deal of water would have been lost at the
surface through evaporation in the heat of the formation process, enough
survived to form the world’s water. It’s an exciting discovery, and one
which we simply didn’t have the technology to make just a few years
ago. We’re looking forward to further research in this area in the
future."
The paper, titled 'Evidence for primordial water in
Earth’s deep mantle', is published in Science. The research was funded
by The University of Hawaii NASA Astrobiology institute under a
Cooperative Agreement.