London: Confirming the theory that ice may
have covered the entire earth in ancient time, geologists have
found evidence that sea ice extended to the equator 716.5
million years ago.
Based on an analysis of ancient tropical rocks that are
now found in remote northwestern Canada, a study by scientists
at Harvard University bolster the theory of `snowball earth`
which say that our planet has, at times in the past, been
ice-covered at all latitudes.
The team was able to determine, based on the magnetism
and composition of these rocks, that 716.5 million years ago
the rocks were located at sea-level in the tropics, at about
10 degrees latitude.
"Climate modelling has long predicted that if sea ice
were ever to develop within 30 degrees latitude of the
equator, the whole ocean would rapidly freeze over," lead
author Francis Macdonald said.
"So our result implies quite strongly that ice would have
been found at all latitudes during the Sturtian glaciation,"
Macdonald said.
This is the first time that the Sturtian glaciation has
been shown to have occurred at tropical latitudes, providing
direct evidence that this particular glaciation was a
`snowball earth` event, journal Science reported.
"Our data also suggest that the Sturtian glaciation
lasted a minimum of five million years," Macdonald added.
According to Enriqueta Barrera, program director in
NSF`s Division of Earth Sciences, which supported the
research, the Sturtian glaciation, along with the Marinoan
glaciation right after it, are the greatest ice ages known to
have taken place on Earth.
"Ice may have covered the entire planet then," says
Barrera, "turning it into a `snowball earth.``
The survival of eukaryotes -- life forms other than
microbes such as bacteria -- throughout this period suggests
that sunlight and surface water remained available somewhere
on earth`s surface. The earliest animals arose at roughly the
same time.
Even in a snowball earth, Macdonald says, there would
be temperature gradients, and it is likely that sea ice would
be dynamic: flowing, thinning and forming local patches of
open water, providing refuge for life.
"The fossil record suggests that all of the major
eukaryotic groups, with the possible exception of animals,
existed before the Sturtian glaciation," Macdonald says.
Scientists don`t know exactly what caused this
glaciation or what ended it, but Macdonald says its age of
716.5 million years closely matches the age of a large igneous
province -- made up of rocks formed by magma that has cooled
-- stretching more than 1,500 kilometres (932 miles) from
Alaska to Ellesmere Island in far northeastern Canada.
This coincidence could mean the glaciation was either
precipitated or terminated by volcanic activity.
PTI
