The following is from Nature Contents this morning.
Al.
Accretion of the Earth and segregation of its core
Bernard J. Wood
1, Michael J. Walter
2 and Jonathan Wade
2
Top of page Abstract
The Earth took 30–40 million years to accrete from smaller 'planetesimals'. Many of these planetesimals had metallic iron cores and during growth of the Earth this metal re-equilibrated with the Earth's silicate mantle, extracting siderophile ('iron-loving') elements into the Earth's iron-rich core. The current composition of the mantle indicates that much of the re-equilibration took place in a deep (> 400 km) molten silicate layer, or 'magma ocean', and that conditions became more oxidizing with time as the Earth grew. The high-pressure nature of the core-forming process led to the Earth's core being richer in low-atomic-number elements, notably silicon and possibly oxygen, than the cores of the smaller planetesimal building blocks.
Editor's Summary
15 June 2006
To the centre of the Earth
Observations of newly formed stars suggest that the Sun's planetary system began life as a flat disk of gas and dust that quickly (in about 100,000 years) accreted to form planetesimals about 10 km in diameter. The Earth was then formed by accretion of planetesimals in a process taking 30–40 million years. Wood
et al. review recent work on the nature of the accretion process, and how the Earth developed an iron-rich molten core richer in low-atomic-number elements than the planetesimal building blocks.
![[1ponders]'s Avatar](../vbiis/customavatars/avatar45_9.gif){kind=avatar}
). Its interesting to follow the to-ing and fro-ing of scientific method!
