Branches and Scope of Geology Questions and Answers

Answer: A

Correct answer: younger beds overlie older ones

Sediment accumulates from the bottom up, so in a sequence that has not been overturned each bed is younger than the one beneath. The qualification matters: intense folding can invert a sequence entirely, which is why criteria for the way up - graded bedding, ripple marks, sole structures - are looked for before the law is applied.

Answer: B

Correct answer: the order of events without their ages in years

Relative dating establishes sequence from superposition, cross-cutting relationships and fossil content, and it was the whole of stratigraphy before radiometric methods existed. Absolute dating attaches numbers of years to that framework. The two are complementary: the order is usually the more secure, the ages the more informative.

Answer: C

Correct answer: longest to shortest division

The hierarchy runs eon, era, period, epoch and age, each a subdivision of the one before. So the Phanerozoic eon contains the Mesozoic era, which contains the Cretaceous period, which contains its own epochs. The ordering is by rank rather than by age.

Answer: D

Correct answer: 4.6 billion years

The figure comes chiefly from radiometric dating of meteorites, which formed at the same time as the earth and have not been reworked since; the oldest terrestrial rocks are somewhat younger because the early crust has been destroyed. The 13.8 billion figure is the age of the universe, not of the earth.

Answer: A

Correct answer: about seven eighths of geological time

The Precambrian runs from 4,600 to 541 million years ago - some 4,060 million years, or 88 per cent of the whole. That the familiar fossil-bearing record occupies only the last eighth is worth keeping in mind: most of the earth’s history is comparatively poorly known.

Answer: B

Correct answer: 80 degrees

\[ T = 20 + 30 \times 2 = 80\ \mathrm{^\circ C}. \] A straightforward calculation with a real consequence: a tunnel at this depth will have a rock face at 80 degrees, which is above what people can work in without ventilation and cooling.

Answer: C

Correct answer: 6 km

\[ z = \frac{200 - 20}{30} = 6\ \mathrm{km}. \] The linear extrapolation is reasonable within the upper crust but not beyond it - the gradient decreases substantially with depth, so applying this arithmetic to tens of kilometres gives temperatures far above the truth.

Answer: D

Correct answer: 12 per cent

\[ \frac{541}{4600} = 0.118, \] that is about 12 per cent. The Phanerozoic - the eon of visible life, containing every period from the Cambrian onwards and effectively the whole of the familiar fossil record - occupies only the last ninth of the earth’s history.

Answer: A

Correct answer: 5

\[ \frac{35}{7} = 5. \] The contrast is fundamental: continental crust is thick, old, low in density and granitic, while oceanic crust is thin, young, denser and basaltic. That difference in density and thickness is what keeps the continents standing above sea level.

Answer: B

Correct answer: 0.55 per cent

\[ \frac{35}{6370} = 0.0055, \] just over half a per cent. The crust on which everything we build stands is a very thin skin indeed - proportionally thinner than the skin of an apple - and the comparison is worth making whenever the crust is spoken of as though it were a substantial part of the earth.