NAT. SCI. 3 – Earth Science and Astronomy

CHAPTER II:Earth Materials and Time

RONALDO T. BIGSANG, M.Sc.

GEOLOGIC TIME:Earth’s Story in the Rocks

OBJECTIVES

• Identify some important geologic events in the history of planet Earth;

• Appreciate the role of fossil records and rock formations in understanding Earth’s past;

• Describe the ways to measure geologic time;• Discuss some principles used to explain relative

geologic time; and• Trace the Earth’s chronologic geological story in a

geologic column.

EARTH ROCKS & MASS EXTINCTIONS

• mass extinction– sudden, catastrophic event when a significant part of

all life-forms on Earth becomes extinct– examples

• meteorite impact• volcanic eruption• increased CO2 levels in the atmosphere

• fossils– remains of prehistoric life imprinted/preserved in

sedimentary rocks

EARTH ROCKS & MASS EXTINCTIONS

EARTH ROCKS & MASS EXTINCTIONS

EARTH ROCKS & MASS EXTINCTIONS

GEOLOGIC TIME

• relative age– an approach to measure geologic time based on the

order in which events occurred– not measured in years– principle: in order for an event to affect a rock, the rock

must exist first• absolute age– tells both the order in which events occurred and the

amount of time that has passed since they occurred– measured in years

RELATIVE GEOLOGIC TIME• principle of original horizontality

– sediments usually accumulate in horizontal layers

• principle of superposition– sedimentary rocks become younger from top to bottom

• principle of crosscutting relationships– a rock must exist before anything can happen to it

• theory of evolution– life-forms have changed in their physical and genetic characteristics over

time

RELATIVE GEOLOGIC TIME

RELATIVE GEOLOGIC TIME

RELATIVE GEOLOGIC TIME

RELATIVE GEOLOGIC TIME

• principle of faunal succession– species succeeded one another through time in a

definite and recognizable order

UNCONFORMITIES & CORRELATION

• conformable – describes sedimentary layers that were deposited continuously without

detectable interruption

• unconformity– an interruption in sediment deposits causing a gap in the geological

record for that place– disconformity

• sedimentary layers above and below the unconformity are parallel– angular unconformity

• younger sediment or sedimentary rocks rest on the eroded surface of tilted or folded older rocks

– nonconformity• layered sedimentary rocks lie on an erosion surface cut into igneous or

metamorphic rocks

UNCONFORMITIES & CORRELATION

UNCONFORMITIES & CORRELATION

UNCONFORMITIES & CORRELATION