Could meteorites have brought water to Earth?
Scientists now believe that water on Earth came from meteorites. The theory has earlier been difficult to prove because the meteorites that came in contact with Earth didn't contain any water.
However, the evidence of water movement in meteorites that recently collided with Earth has taken scientists by surprise.
According to a report in phys.org, a team of researchers found evidence of relatively recent water movement in meteorites that collided with the Earth in more recent times.
In a paper published in the journal Science, researchers said they studied isotopes in carbonaceous chondrite (CC) meteorites that have landed on Earth over just the past century. They analysed uranium and thorium distributions in samples -- the former is water-soluble while the latter is not -- to find out if recently arriving meteorites have evidence of water movement.
According to the National Aeronautics and Space Administration (NASA), when a meteoroid -- objects in space that range in size from dust grains to small asteroids -- survives a trip through the atmosphere and hits the ground, it's called a meteorite.
When meteoroids enter Earth's atmosphere (or that of another planet, like Mars) at high speed and burn up, the fireballs or "shooting stars" are called meteors.
Meteorites are characterised by their carbon compound. "Among stony meteorites are the chondrites which contain small round spheres called chondrules. These small spherules are principally made up of olivine and pyroxene [minerals made up of Mg, Fe and silicate]. The carbonaceous chondrites are composed not only of inorganic minerals but have a high abundance of carbon," researchers said while describing CC meteorites.
Scientists believe that if water ever existed in the meteorite, "it would have had to move as it melted, and that movement would be reflected in the distribution of thorium and uranium isotopes," the report said.
Both these isotopes have short half-lives, which means that if their distributions in meteorites could be found, they would have occurred relatively recently on the order of a few million years.
Researchers studied nine meteorites and found that water moved due to melting, likely within the past 1 million years.
Not only could such meteorites have delivered water to Earth during the planet's formative years, they could also have been doing so in the much more recent past.
Researchers further said that to confirm the findings, this idea could be tested by sampling asteroids before they strike the Earth -- as done recently by Japanese and American spacecraft.
Initial studies suggested that most, if not all, carbonaceous chondrite (CC) -- class of chondritic meteorites comprising at least 8 known groups and many ungrouped meteorites -- were formed approximately 4.5 billion years ago as part of larger asteroids.