Transcript Time Scale (1)

Building the Geologic Timescale
1.8 mya
65 mya
245 mya
545 mya
LAW OF SUPERPOSITION - STENO
In a layered succession of strata, any individual unit will
be younger than the one below it and older than the one
above it, unless the rocks have been folded or overturned.
LAW OF SUPERPOSITION
Younger
Older
The Law of faunal
Succession - Smith
In the geologic record, fossil
faunas succeed on another in
an orderly and determinable
fashion. Therefore, rocks of
different ages have different
fossil faunas.
The Principle of Fossil Correlation –Smith & Cuvier
Similar assemblages of fossils are similar ages, and
thus the rocks that contain them are of similar ages.
Law of Cross-Cutting Relationships – Hutton
A rock unit or structure is older than any rock unit or structure that
cuts across it.
Law of Inclusions – Steno
A rock or fossil that occurs as an inclusion within another rock must
be older than the rock that surrounds it.
Fig. 5.1
UNCONFORMITIES
Evidence of missing time in the Geologic Record
Different types of Unconformities
Fig. 4.21
Disconformity
Angular
unconformity
Nonconformity
The Kant/LaPlace Hypothesis of Solar System Formation (1755)
The nebula condenses into a swirling disc,
p.26-27a
with a central ball surrounded by rings.
Forming the solar system, according to
the nebula hypothesis: A second- or thirdgeneration nebula forms from hydrogen
and helium left over from the big bang, as
well as from heavier elements that were
produced by fusion reactions in stars or
during explosion of stars.
The ball at the center
grows dense and hot
enough for fusion
reactions to begin. It
becomes the Sun. Dust
(solid particles)
condenses in the rings.
p.26-27b
Dust particles
collide and stick
together, forming
planetesimals.
Gravity reshapes the
proto-Earth into a
sphere. The interior of
the Earth separates into
a core and mantle.
p.26-27c
Forming the panets from planetesimals:
Planetesimals grow by continuous
collisions. Gradually, an irregularly
shaped proto-Earth develops. The
interior heats up and becomes soft.
Soon after Earth forms, a small planet
collides with it, blasting debris that forms
a ring around the Earth.
The Moon forms from the ring of debris.
p.26-27d
RANGES OF EARTH AGES PRE-1900