Transcript How do we know the age of the earth?

Aim: How do we know the age of the Earth?
I. Earth’s History
A. Uniformitarianism – the principle that most
of the geologic events of the past are similar
to the processes that we can observe in the
present.
B. The Law of Superposition – says that
the rock layers on the bottom of an
undisturbed rock exposure are usually the
oldest.
1. From this knowledge, geologists can date
the relative ages of the strata (layers) from
bottom to top (oldest to youngest).
youngest
oldest
“Rock is always older than the processes
that changed it.”
C. Igneous Intrusions and Extrusions
1. Intrusion – created when magma is injected
into older rock layers in the crust.
2. Extrusion – igneous rock that formed
from lava at the surface of the crust.
D. Folds and Faults
1. Folds are bends in rock strata.
Sometimes folding can overturn rock strata
so that older rock lies on top of younger
rock.
2. Fossils – any naturally preserved
remains or impressions of living things.
a. Sometimes the remains of the whole
organism are found in sap (insects), tar
pits, ice.