For the first time, a unique study conducted at Lund University in Sweden
has tracked the meteorite flux to Earth over the past 500 million years.
Contrary to current theories, researchers have determined that major
collisions in the asteroid belt have not generally affected the number of
impacts with Earth to any great extent.
Researchers have been studying geological series since the 19th century in
order to reconstruct how flora, fauna and the climate have changed over
millions of years. Until now, however, almost nothing has been known about
ancient meteorite flux - which makes sense since impact is rare, and the
battered celestial bodies quickly break down as they encounter Earth's
oxygen. A new study published in PNAS shows how researchers in Lund have
reconstructed meteorite bombardment towards Earth over the past 500 million
years.
"The research community previously believed that meteorite flux to Earth was
connected to dramatic events in the asteroid belt. The new study, however,
shows that the flux has instead been very stable", says Birger Schmitz,
professor of geology at Lund University.
To conduct the study, researchers at Lund University's Astrogeobiology
Laboratory dissolved almost ten tonnes of sedimentary rocks from ancient
seabeds in strong acids because the sediment contains residue from the
meteorites dating back to when they fell to Earth.
Meteorites contain a small fraction of a mineral, a chromium oxide, which is
very resistant to degradation. The microscopic chromium oxide grains were
sifted out in the laboratory and serve as time capsules with an abundance of
information.
"The dissolved sediment represents 15 periods over the past 500 million
years. In total, we have extracted chromium oxide from almost 10 000
different meteorites. Chemical analyses then enabled us to determine which
types of meteorites the grains represent", says Birger Schmitz.
A couple of thousand meteorites land on the Earth's surface every year, and
approximately 63 000 space rocks have been documented by science. The space
rocks originate from the asteroid belt between Mars and Jupiter where
battered celestial bodies from gigantic collisions revolve around the sun.
"We were very surprised to learn that only one of the 70 largest asteroid
collisions that took place over the past 500 million years resulted in an
increased flux of meteorites to Earth. For some reason, most of the rocks
stay in the asteroid belt", says Birger Schmitz.
The study not only upends generally accepted meteorite flux theories; it
also provides entirely new perspectives on which types of celestial bodies
are at greatest risk of colliding with Earth and where in the solar system
they originate. From a geological time perspective, kilometre-sized
celestial bodies collide with the Earth on a regular basis. One such event
took place 66 million years ago, when a celestial body stretching over 10
kilometres in size hit the Yucatán Peninsula. The impact was part of the
reason the Earth went dark and dinosaurs starved to death.
"Future impact from even a small asteroid for example in the sea close to a
populated area could lead to disastrous outcomes. This study provides
important understanding that we can use to prevent this from happening; for
example, by attempting to influence the trajectory of rapidly approaching
celestial bodies", concludes Birger Schmitz.
Reference:
Asteroid break-ups and meteorite delivery to Earth the past 500 million
years
Fredrik Terfelt and Birger Schmitz
PNAS 118 (24) e2020977118;
https://doi.org/10.1073/pnas.2020977118
Tags:
Space & Astrophysics