What is Deep Time?
❖ Most geoscientists
view Deep Time as
pertaining to the preQuaternary (>10ka [104])
❖ Last 10ka witnessed a
short duration under
anomalous conditions of
an Icehouse climate state
❖Earth processes operate on a continuum of temporal,
spatial, and parametric scales represented in records on the
order of 104-106
❖Long-term records of Earth’s dynamic state; preserves the
results of multiple large-scale experiments in environmental
change
❖ Deep time records
showcase:
CHAPMAN’S PEAK
LAINGSBURG
❖ Environmental disturbances unknown
from the recent
❖ Feedbacks that occur on longer time
scales in response to perturbation that
are different than those observable
today (pre-human responses)
❖ Earth Systems
❖ Synergistic physical system of
interrelated phenomena
❖ Governed by complex processes
involving the geosphere, atmosphere,
hydrosphere, cryosphere, and biosphere
❖ Interactions of chemical, physical,
biological and dynamical processes
extending over spatial & temporal scales
How is Deep Time told?
542
PALEOZOIC
252.6
MESOZOIC 66.5 CENOZOIC
❖Geochronology
❖ The organization of exposures of rocks into a standard
chronological sequence
❖ The science of dating and determining the time sequence of
events in the history of the Earth (Neuendorf et al. 2005)
❖ Assembled from rock sequences stacked and segmented into
relative units based on their unique fossil and physical content.
Is it like African Time?
❖ Before radiometric dating
techniques, the Geologic
Column was assembled based
upon the basic Laws of
Stratigraphy (Steno 1631-1687)
❖ Law of Superposition
❖ Law of Original Horizontality
❖ Law of Original Lateral Continuity
❖ Principle of cross-cutting
relationships
❖ Principle of inclusions
Geochronology & Biostratigraphy
PERMIAN-TRIASSIC
VERTEBRATE
ZONATION
❖ Fossil Assemblages of
various unique organisms
exhibit an unique
stratigraphic range in the
rock record
❖ Biostratigraphy groups
events into zones, and show
only the events that define
zone boundaries
❖ Advances in
computational algorithms
allow for stratigraphic
sequencing of large data sets
with increased reproducibility
Or, is it measured like
Western time?
❖ GEOCHRONOMETRY
❖ Methods to determine numerical
intervals of geologic time in units of years
(Zalasiewicz et al., 2004)
❖EARTH-TIME Project refining numeric dates to within
100,000 years
❖Restructuring of Deep Time
❖Astronomical “tuning” – Earth’s orbital motion affects the development of the
rock record (back 40 myr)
❖Changes in Earth’s angle of the globe’s spin axis, the path of its orbit, and
the orientation of its axis relative to the Sun change cyclically and, in turn,
influence climate.
GEOCHRONOLOGY = RADIOMETRIC
DATING
❖ Isotopes differ in #
neutrons; stable & unstable
❖ Spontaneous decay
❖ Parent-to-Daughter
❖Loss of Alpha particle
❖Helium atom (2p, 2n; At # -2; At
Mass -4)
❖Loss of Beta particle
❖Electron loss turns neutron to
proton (At # +1; At mass 0)
❖Capture of Beta
❖Turns proton to neutron (At # -1;
At mass 0)
❖Rubidium87 -Strontium 87
4.944 x 1010
❖Traceamounts in Igneous &
Metamorphic Rx; >100 MY
❖Thorium232 - Lead 208
1.401 x 1010
❖Zircons widespread in
Igneous & Metamorphic Rx
If so, How? 1 ⎛ D⎞
t = ln⎜1 + ⎟
λ ⎝ P⎠
Where :
t = the age of the rock/mineral
D = number of atoms of daughter product
P = number of atoms of parent
ln = natural log
1/ 2
λ = decay constant
t
=
ln 2
λ
❖Potassium 40 - Argon 40
1.25 x 109
❖Uranium 238 - Lead 206
4.468 x 109
❖Zircons widespread in
Igneous & Metamorphic Rx
❖Uranium 235 - Lead 207
7.038 x 109
❖Zircons widespread in
Igneous & Metamorphic Rx
❖Carbon 14 - Nitrogen 14
5730 Yr
African Time with Western Numeric Function:
Non-Radiometric Dating Techniques
❖ Varved deposits
❖ Sediment couplet of
summer (coarse) & winter
(very fine from suspension)
clastics
❖ Deposited in response to
yearly fluctuation in
sedimentation.
❖ Capable of determining
lake histories (e.g., Lake
Baikal >200,000 varves).
Why is it
important
for South
Africa?
23
65.5
145
199
252.6* (+/- 0.2)
299
359
416
444
488
542
Dates after Gradstein et al., 2004
* after Mundil et al. 2004