The Origin of the Earth |
Nowadays it is considered that the Earth was created in
the process of accretion 4.5 billion years ago.
The theory of accretion was invented by Otto Schmidt,
Russian geophysicist, and published in 1944. It was recalled in the 1960s, after the
Apollo space program. According to the theory, the cosmic dust clusters, creating bigger
particles. The particles merge into pieces of rocks, then bigger balls, planetesimals and
finally planets. As the planets grew bigger, the quantity of loose material and thus the
amount of collisions decreased.
As can be seen from the above, it took time to build a
large planet like the Earth.
In the 1950s, Clair Patterson detected that meteorites
have the same lead isotope content as the Earth. Using uranium-lead clock he stated age of
the Earth (and meteorites) as 4.55 billion years.
The oldest meteorites that constituted the Earth are
about 4.56 billion years old, but our planet had been continuing to grow for the next 120
- 150 million year. Then, 4.4 - 4.1 billion years ago the core and the atmosphere were formed, which preceded the appereance of
the continents.