Chapter 9

what is the principle we use to determine the age of a landscape surface?

a surface wit ha well-developed soil is probably older than a surface with no soil.

What was the Cambrian explosion?

a time when many different types of creatures appeared on Earth.

in this photograph, Paleozoic sandstone rests depositionally on Precambrian granite. What events must have occured before deposition of the sandstone?

All of the above.

what is the main geologic feature for which Siccar Point in Scotland is famous?

All of the above; a bountry between steep gray layers below and gently red layer above, b) unconformity, c) ancient erosion surface.

if a rock started with 1,000 atoms of a parent but now contains 250 atoms, how many half lives have passed?

2 half lives

what would fossil ages from the geologic timescale tell us about the age of this unconformity?

all of the above.

which of the following is evidence that Earth's history is not short?

all of the above.

this figure shows two sections that partially overlap in age. Dashed lines show how the two sections correlate. What can you conclude from this correlation?

the left section represents older rocks than the right section.

this figure shows two fault scarps, a lava flow, and erosion along one of the scarps. What is probably the oldest feature of those listed below?

the scarp on the right.

what factors are the most critical in determining whether a fossil is preserved?

whether the creature had hard parts and how fast it was buried.