Scientists
have uncovered a 'lost continent' in Africa that dates back billions of
years, to one of the earliest periods in earth's history.
A fleck of iridescent zircon that is embedded in a piece of trachyte. Credit: Wits University
A 3-billion-year-old "lost continent" lurks beneath the Indian Ocean island of Mauritius, new research confirms.
Sparkly, iridescent flecks of rocks known as zircons from Mauritius
date back billions of years, to one of the earliest periods in Earth's
history, the researchers found. Other rocks on the island, by contrast,
are no more than 9 million years old.
"The fact that we have found zircons of this age proves that
there are much older crustal materials under Mauritius that could only
have originated from a continent," Lewis Ashwal, lead author of the
new study and a geologist at the University of the Witwatersrand,
Johannesburg in South Africa, said in a statement.
Earth's crust is made up of two parts: the planet's continents,
which rise high above the oceans because they are composed of lighter
rocks such as granite; and the ocean basins, which sink lower because
they are made up of denser rocks such as basalt, according to a video
about the new study. Whereas the continental crust may be 4 billion
years old, oceanic crust is much younger, and is continually being
formed as molten rock spews through fissures in the ocean floor, called
midocean ridges.
The traditional thinking is that the island of Mauritius was formed
by volcanic activity stemming from one of these midocean ridges,
meaning older crust shouldn't be there.
But the new study suggests that a tiny sliver of a primeval
continent might have been left behind when the supercontinent Gondwana
split up into Africa, India, Australia and Antarctica more than 200
million years ago. Then, the fiery birth of the island blanketed the
primeval rock in layer after layer of cooling lava, building up the bulk
of the island that is visible today, the researchers said.
"According to the new results, this breakup did not involve a
simple splitting of the ancient supercontinent of Gondwana, but rather a
complex splintering took place, with fragments of continental crust of
variable sizes left adrift within the evolving Indian Ocean basin," Ashwal said.
The new findings buttress results from a 2013 study that also found
traces of ancient zircons in beach sand on the relatively young island.
However, critics contended that this zircon could have traveled there
in trade winds or been carried along on someone's shoes. In the new
study, however, the zircons were found embedded in 6-million-year-old
rock known as trachyte, ruling out the notion of wind-blown transfer,
Ashwal said.
The findings were published Tuesday Jan. 31 in the journal Nature Communications.
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