Transcript Relative dating cross cutting relationships

RELATIVE DATING
What is it ?
Who Dunit ?
James Hutton
Let’s start with the story of James Hutton, a wealthy
farmer born in 1726. As a farmer, it brought him into
close contact with the land
Holyrood Park
Edinburgh Castle
James Hutton’s Revelation
He was the first
person to realise
that the Earth must
have been very much
older than the 6,000
years believed at
that time
Hutton’s Imagination
Hutton was convinced
that the lowlands of
Scotland had been made
at a later time than the
uplands, but he did not
have any proof
UNTIL …
Siccar Point, Nr Edinburgh
Whilst walking along
the beach at Siccar
Point, he noticed that
the pebbles had come
from the cliff – he now
understood that the
beach sand was made
from the eroding cliffs
– that was a big leap of
imagination for its time
Hutton’s Story of Siccar Point
He then noticed around the
corner from the beach that
some gently dipping red
sandstones were lying on top
of some grey-coloured
upright layers
From his observations, he began to unravel the
story of what had happened to these rocks
RELATIVE DATING
PRACTICAL
So, what is Hutton’s Story ?
The grey-coloured beds
(A) were laid down as
horizontal layers of soft
muds in the sea.
A
These were hardened
into rock deep in the
Earth and then buckled
into folds by immense
stresses.
So, what is Hutton’s Story ?
These stresses also
thrust the rocks up to
the surface as great
mountains, which were
then eroded.
B
A
These mountains were
likewise worn down, and
formed the horizontal
red beds (B) on top of
the vertical grey rocks.
So, what is Hutton’s Story ?
What is his evidence?
A
B
A
A
A
A
Fragments of the
folded grey rock (A)
are found in the red
beds above it (B) – so
the red beds must be
younger.
He didn’t even need fossils to date his beds !
Fold Shape
ANTICLINE
SYNCLINE
younger
younger
older
older
What do you think
produces folds ?