Transcript F08 11 time - Department of Earth & Environmental Sciences

Unraveling Deep Time
How to look back at the Earth’s past
ERTH 1010/1100
JD Price
New and old
The dynamic nature of the Earth’s surface means that
conditions change. Basins may become mountains, and
vice-versa. Rocks preserve information about their past;
a past similar to the present.
Looking back
• Minerals - Preserve the physiochemical signature of their origins
• Fossils - Record temporally and spatially constraints, as well as
environmental factors.
• Rocks - retain information about the environment of their formation
and their ability to deform
• Structures - preserve info about the forces at work in the Earth
• Temporal relationships - sediments layer, igneous dikes and faults
cut layering, streams incise, and glaciers strip.
• Geochemical transfer - the movement of components from
minerals to melts or other minerals to global scale trends
• Geodynamics - measurement of current motions may be “run
backwards.” Constrain past Earth
• Geophysical observations - give us the clearest picture of the
Earth today and yield clues to the past.
Unraveling the past
Logical relationships
Missing time - unconformity
•
•
Angular Unconformity - missing time on structures
Nonconformity - missing time on a non-sedimentary surface
Missing time
The age of the rocks
may change sharply.
These are
unconformities in
time, and often reflect
periods of no
deposition or erosion.
Recall that the bulk of
sediments involve
water. Lack of
deposition may reflect
local drying.
•
Disconformity - missing time on horizontal surfaces
Clues to the past
Old and new
420 Ma
Rocks preserve the remains of older life some different from those found today,
others very similar to modern forms
Australia 2007
Fossils
The remnants of many organisms are left behind in
accumulating sediments. Skeletal materials, made of dense
minerals can be particularly well preserved. In places entire
ecosystems are buried and lithified.
Note: these are categorized by morphology and environment (not
genetics)
Q: what type of rock is this?
Fossilization Bias
Keep in mind the fossil record is by no means an accurate
depiction of ancient life
Fossilization favors Organisms
with simple skeletons or hard parts (few pieces)
in aquatic environments with rapid deposition
that are small enough to buried quickly
that are abundant and well distributed
that existed over substantial periods of time
Note the oldest observed fossil certainly may not be the oldest individual
for that organism
Note fossils contain no organic materials*; there is only a little chemical
evidence to be gleaned from them.
*with rare, young exceptions
It’s not all dinosaurs
In fact, large fossils
require more
information than they
typically provide.
Microscopic fossils like
conodonts,
radiolarians, cocoliths,
and pollen spores can
be much more
definitive and
revealing.
It’s not always living
Trace fossils - the preserved
“imprints” of organisms.
Burrows, nests, and trails
(like Ediacaran).
Some organisms are known
only by their trace
Climactichnites (505 Ma New York).
FIY - New York is home to many of
the definitive fossils of the oldest era the Paleozoic
New York’s Fossil
The Eurypterid - (sea scorpion)
up to 2m (over 6 feet) in length,
the predator of the Silurian age
Well preserved fossils are found
from the Ordovician to Permian
ages. Fresh-brackish water,
possibly land.
Fossils and Jurassic Park
`
•While mesozoic amber (crystallized and partially
replaced tree sap) does exist, it is mostly of
Cretaceous (younger) age
•Insect skeletal parts may be preserved, but little
to none of the soft tissue.
•No one has successfully characterized a small
portion of the insect’s DNA, let alone any
digested matter from living organisms.
•The oldest analyzable DNA found is 395,000
years old. These are fragments from plant
spores trapped in Siberian permafrost.
While Michael Crichton does write an entertaining story, he’s always fast and loose with the
science. On the positive side, he has brought more popular attention to a number of scientific
endeavors. But he’s big on the “Frankenstein” plotline - tinkering with “nature” is inherently
wrong, and only highlights the feeble aspects of human activity. However, adapting nature is a
natural response of all organisms.
Fossil yeast
Raul Cano, now at Cal Poly, extracted a
yeast colony from a 45 Ma Lebanese
weevil covered in amber.
Activating the ancient yeast, Cano now
brews barrels of pale ale and German
wheat beer through the Fossil Fuels
Brewing Company.
Supposedly - the yeast break down
sugars differently than their modern
descendants. It gives the beer a unique
taste.
“the first Jurassic Park sequel you'll actually be
able to swallow.” - The Washington Post
Time and fossils
By the early 1800’s, it became clear that the Earth
had a long history preserved in the rocks.
Many of these organisms exhibited small changes in
morphology with time
The complexity of life increased with time
People started to wonder how this diversity could
arise through natural processes.
Lamarck theory
Jean Baptiste Pierre Antoine de Monet, Chevalier de Lamarck
Lamarck advocated that organisms could adapt within a
generation. Traits developed as adaptations to the
environment. These are passed to offspring (in a sense, he
was right about bacteria)
Figure 24.16a
24-513a
Darwin-Wallace
Theory
Charles Darwin
Alfred Russel Wallace
Darwin and Wallace concluded that adaptations were
multigenerational. Organisms that could not overcome
changes in requirements died out, removing their hereditary
traits from a population
Figure 24.16b
24-513b
150 years ago at RPI
A course called Physical
Geography
•Darwinian evolution
•Lamarkian evolution
•Multiple origins
Evolution’s politics
Darwin-Wallace evolution has been summarized as
“survival of the fittest.” Organisms that can’t adapt, die,
and in most cases won’t reproduce.
True story: In the early 1930’s, the Soviet Union
developed an agricultural process under T.D. Lysenko
based on Lamarkian evolution, purportedly because
Darwinian evolution was contrary to Stalinist ideals.
Lysenko claimed that winter wheat would adapt into
spring wheat if planted later in the year. (He also later
claimed that wheat would transform into barley or rye
given the right conditions). The results were
devastating.
Q: What is the difference between
Lamark and Darwin-Wallace theories?
Eugenics
The application of genetic heredity to human breeding
Stipulating that some individuals are deemed unworthy
of contribution to the gene pool
“Survival of the fittest” and who decides what fit is
This was embraced by many in the US, early 1900’s
The Scopes Trial, 1925 - a reaction to Eugenics
Tennessee passes a law prohibiting the teaching of
evolution theory ($100-$500 fine). Evolution equated to
eugenics
John Scopes, football coach and substitute bio teach
was guinea pig for town of Dayton and ACLU
Example of selection
Short clovers are selected on the side of the fence with
the cows, because the long phenotype is removed.
Figure 24.9
24-509
Artificial selection
Selection was not a
new idea in Darwin’s
time. The first chapter
of The Origin of
Species discusses
breeding and
husbandry
development of
domesticated animals.
All members of C. familiarus are likely descendents
of wolves in or near China 15,000 years ago.
Darwin and Wallace
saw the same
processes with the
environment choosing
the preferred features
of the offspring.
Gradualism’s weakness
The traditional view of natural selection means that small
changes to organisms would happen all the time. If organism
A is related to Organism C, then there should be some
intermediate organism (B) that links the two and shows the
gradual progression.
Much of the fossil record does not show this. Many
morphological types of organisms (i.e. species) persist for
long periods of time in the fossil record. Organisms appear
and disappear quite quickly.
In the early seventies, Niles Eldredge and Stephen Gould
suggested that adaptation happens very quickly – giving rise
to organisms that are well suited for long periods of time
Punctuated equilibrium
Punctuated Equilibrium
1. Modern life constrains the ancient
2. New species split from populations
3. Most new species are in geographical isolation.
4. Large, widespread species usually change slowly, if at all.
5. Daughter species are typically geographically limited.
6. Daughter species limited in time
7. The fossil record largely static with few rapid changes.
8. Adaptive change in lineages occurs with speciation.
9. Trends in adaptation occur mostly through species selection.
Gradualism
Punk Eek
Q: what’s the
difference?
Speciation
Most new
species arise
from a single
species that
becomes
geographically
divided.
Q: in what ways
would plate
tectonics
influence
evolution?
Figure 24.14
24-511
Fossils and time
An index fossil is the
remains of an organism
widely distributed on
Earth for a short amount
of time.
Time correlation
Beginning in the 1700’s, geologists were able to recognize that
specific species of fossils can link rocks in time, even if separated by
great distances. This works best for species that existed for short
periods of time over large part of the Earth.
Correlation
Layers of rocks may
be traced from
location to location
Geometries may
change with
individual
environments.
Sediments and time
Rocks that contain fossils result from the
gravitational settling of particles in water
In the modern world, this is a very slow process
(but variable depending on local energies).
It became clear from these rocks that earth was
a very old place
But how old?
Note: Lord Kelvin’s estimate of a cooling earth
(~100 Million Years) - too fast. What did he
miss?
Radiochronography
Atoms come in several flavors: some have too many or too few
neutrons in their nucleus in an unstable configuration. These
will change into a stable atoms with time.
14C
is created from 14N
when radiation from the
sun interacts with upper
atmosphere
14C
14C
-›
14N
decays back over time. One of the neutrons becomes a
proton, an electron ( particle) is kicked out
Half of the
14C
is gone in 5730 years
+
Isotopes
Long half lives
There are a number of other
radioisotopes that are more useful for
examining deep time.
235U
207Pb
0.704 Ga
236U
208Pb
4.468 Ga
40K
40Ar
1.251 Ga
87Rb
87Sr
48.8 Ga
Note: uranium decay has complicated
route through several unstable atomic
configurations.
Measurement is similar for all, count atoms (lots
of atoms) separated by their mass.
Count the initial element and daughter atoms and calculate
how many years it took to make the current concentrations.
Fine time
Magnetism
Compiling info
Radiometric
dating - easy
from igneous
rocks
Fossil
information for
young materials
Magnetic
reversals
Time Scale
Precambrian the time before
the abundant
fossil record.
It’s most of
Earth history but
the information
is more obscure.
Grand Canyon
•
The layering in the grad canyon shows a succession of rocks ranging from very
old metamorphic and igneous rocks to much younger sedimentary rocks.
Grand Canyon
Equivalent times - larger systems
The Canyonlands
Canyonlands Layers