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Topic Name: Early formation of Earth may answer an age-old question about the planet’s mantle
Category: Environmental engineering
Research persons: John Hernlund
Location: University of British Columbia, Canada
Details
Observations about the early formation of Earth may answer an age-old
question about why the planet’s mantle is missing some of the matter that
should be present, according to UBC
geophysicist John Hernlund.
Earth is made from chondrite, very primitive rocks of meteorites that date
from the earliest time of the solar system before the Earth was formed. However,
scientists have been puzzled why the composition of Earth’s
mantle and core differed from that of chondrite.
Hernlund’s findings suggest that an ancient magma ocean swirled beneath the
Earth’s surface and would account for the discrepancy.
“As the thick melted rock cooled and crystallized, the solids that resulted
had a different composition than the melt,” explains Hernlund, a post-doctoral
fellow at UBC Earth and Ocean Sciences.
“The melt held onto some of the elements. This would be where the missing
elements of chondrite are stored.”
He says this layer of molten rock would have been around 1,000 km thick and
2,900 km beneath the surface.”
Published in today’s edition of the journal Nature, Hernlund’s study
explores the melting and crystallization processes that have controlled the
composition of the Earth's interior over geological time. Co-authors are Stéphane
Labrosse, Ecole Normale Superieure de Lyon and Nicolas Coltice, Université
de Lyon.
The centre of Earth is a fiery core of melted heavy metals, mostly iron. This
represents 30 per cent while the remaining 70 per cent is the outer mantle of
solid rock.
Traditional views hold that a shallow ocean of melted rock (magma) existed
1,000 km below the Earth’s surface, but it was short lived and gone by 10
million years after the formation of Earth.
In contrast, Hernlund’s evolutionary model predicts that during Earth’s
hotter past shortly after its formation 4.5 billion years ago, at least
one-third of the mantle closest to the core was also melted.
The partially molten patches now observed at the base of the Earth's mantle
could be the remnants of such a deep magma ocean, says Hernlund.
Note for Solar System
The Solar System or solar system consists of the Sun and the other celestial objects gravitationally bound to it: the eight planets, their 166 known
moons, three dwarf planets (Ceres, Pluto, and Eris and their four known moons), and billions of small bodies. This last category includes asteroids, Kuiper belt objects, comets, meteoroids, and interplanetary dust.
In broad terms, the charted regions of the Solar System consist of the Sun, four terrestrial inner planets, an asteroid belt composed of small rocky bodies, four gas giant outer planets, and a second belt, called the Kuiper belt, composed of icy objects. Beyond the Kuiper belt lies the scattered disc, the heliopause, and ultimately the hypothetical Oort cloud.
In order of their distances from the Sun, the planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Six of the eight planets are in turn orbited by natural satellites, usually termed "moons" after Earth's Moon, and each of the outer planets is encircled by planetary rings of dust and other particles. All the planets except Earth are named after gods and goddesses from Greco-Roman mythology. The three dwarf planets are Pluto, the largest known Kuiper belt object; Ceres, the largest object in the asteroid belt; and Eris, which lies in the scattered disc.
Note for Earth's mantle
Earth's mantle extends to a depth of 2890 km, making it the largest layer of the Earth. The pressure, at the bottom of the mantle, is ~140 GPa (1.4 Matm). The mantle is composed of silicate rocks that are rich in iron and magnesium relative to the overlying crust. Although solid, the high temperatures within the mantle cause the silicate material to be sufficiently ductile that it can flow on very long timescales. Convection of the mantle is expressed at the surface through the motions of tectonic plates. The melting point and viscosity of a substance depends on the pressure it is under. As there is intense and increasing pressure as one travels deeper into the mantle, the lower part of the mantle flows less easily than does the upper mantle (chemical changes within the mantle may also be important). The viscosity of the mantle ranges between 1021 and 1024 Pa·s, depending on
depth. In comparison, the viscosity of water is approximately 10-3 Pa·s and that of pitch 107 Pa·s. Thus, the mantle flows very slowly.
About Researcher
John Hernlund
| Tags: |
formation of Earth - planet - mantle - UBC - geophysicist - John Hernlund - Earth mantle - chondrite - Earth surface - Université de Lyon - Solar System - planet’s mantle - Early - answer - age-old question - |
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