The continental growth rate has been calculated to be about 3 km
3 a year during
a period about 4–3 billion years ago but this rate of growth decreased to 0.8 km
3 a
year after the early high growth-rate period (Dhuime et al. 2012). A decrease in the
rate of continental accretion is probably due to the increase in subduction of newly
formed lithospheric plates. The major granite-forming events have taken place
sequentially with intermittent, quieter geological periods. When reading backward
from the present, the major granite-forming events for building the crust can be
dated in millions of years: 100, 400, 1,100, 1,500, 1,900, 2,600 and 3,400 million
years (Gastil 1960; Engel and Engel 1964; Pearson et al. 2008). For example, the
Alps in Europe, and the Andes, Rocky, Cascade and Appalachian mountains in the
Americas are among the youngest examples of continental crust, since they are
only about 100–200 million years old. The oldest granite crust which has been
found in south Greenland, North America, Scandinavia, South Africa and in
western Australia is older than 2.6–3.8 billion years (Hanika et al. 2012) (Fig. 2.5).
Wilde et al. (2001) used evidence from age dating on a detrital zircon
(ZrSiO 2 —zirconium silicate) found in the Narryer Gneiss Terrain, in Yilgarn
Craton, in Western Australia, and have determined that this part of the Earth has an
age of 4.4 billion years old. The Narryer Gneiss Terrain contains sedimentary
rocks suggesting the presence of early water that interacted with ancient continental crust. The zircon’s isotopic age goes back to the time when the zircon’s
magma separated from the mantle, at which point it crystallized. The oxygen
isotope measurements on this zircon suggest that the crystal grew in a liquid
environment. Thus, the presence of water implies that the surface temperature was
Fig. 2.5 The ancient ([0.2–2.5 billion years old) subaerial exposure of continental crust (black)
is compared to younger (\0.2 billion years old) Large Igneous Provinces (grey)
38
2 Our Haven, Planet Earth
3 a year during
a period about 4–3 billion years ago but this rate of growth decreased to 0.8 km
3 a
year after the early high growth-rate period (Dhuime et al. 2012). A decrease in the
rate of continental accretion is probably due to the increase in subduction of newly
formed lithospheric plates. The major granite-forming events have taken place
sequentially with intermittent, quieter geological periods. When reading backward
from the present, the major granite-forming events for building the crust can be
dated in millions of years: 100, 400, 1,100, 1,500, 1,900, 2,600 and 3,400 million
years (Gastil 1960; Engel and Engel 1964; Pearson et al. 2008). For example, the
Alps in Europe, and the Andes, Rocky, Cascade and Appalachian mountains in the
Americas are among the youngest examples of continental crust, since they are
only about 100–200 million years old. The oldest granite crust which has been
found in south Greenland, North America, Scandinavia, South Africa and in
western Australia is older than 2.6–3.8 billion years (Hanika et al. 2012) (Fig. 2.5).
Wilde et al. (2001) used evidence from age dating on a detrital zircon
(ZrSiO 2 —zirconium silicate) found in the Narryer Gneiss Terrain, in Yilgarn
Craton, in Western Australia, and have determined that this part of the Earth has an
age of 4.4 billion years old. The Narryer Gneiss Terrain contains sedimentary
rocks suggesting the presence of early water that interacted with ancient continental crust. The zircon’s isotopic age goes back to the time when the zircon’s
magma separated from the mantle, at which point it crystallized. The oxygen
isotope measurements on this zircon suggest that the crystal grew in a liquid
environment. Thus, the presence of water implies that the surface temperature was
Fig. 2.5 The ancient ([0.2–2.5 billion years old) subaerial exposure of continental crust (black)
is compared to younger (\0.2 billion years old) Large Igneous Provinces (grey)
38
2 Our Haven, Planet Earth