Which of the following is an example of chemical weathering?

freezing and thawing rainwater widens a crack in a sidewalk.
acid rain discolors and disfigures a limestone statue.
a stream rounds and smoothes rocks into pebbles.
a growing tree root splits a boulder in two.

the sun’s energy hits earth’s surface at the most direct angle at which of the following locations?

30° n or s latitude
south pole
north pole
equator
why does temperature increase with altitude through the stratosphere?

the air molecules are closer together in the upper stratosphere.
the stratosphere is closest to the sun.
all layers of the atmosphere increase in temperature with altitude.
the ozone layer is found in the stratosphere.
which gas is the most abundant in earth’s current atmosphere?

oxygen
carbon dioxide
hydrogen
nitrogen
which of the following was a major source of atmospheric oxygen?

decomposition of water
photosynthesis
volcanic eruptions
outgassing
barometers are used to measure which of the following?

humidity
temperature
wind speed
atmospheric pressure
if heat energy is transferred from direct contact between a warm object and a cold object, it has been transferred by

convection
radiation
conduction
the sun