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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.
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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.
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
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. Darwin and Wallace saw the same processes with the environment choosing the preferred features of the offspring. All members of C. familiarus are likely descendents of wolves in or near China 15,000 years ago.
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 andStephen Gould suggested that adaptation happens very quickly – giving rise to organisms that are well suited for long periods of time Punctuated equilibrium
Punctuated Equilibrium • Modern life constrains the ancient • New species split from populations • Most new species are in geographical isolation. • Large, widespread species usually change slowly, if at all. • Daughter species are typically geographically limited. • Daughter species limited in time • The fossil record largely static with few rapid changes. • Adaptive change in lineages occurs with speciation. • Trends in adaptation occur mostly through species selection.
Gradualism Q: what’s the difference? Punk Eek
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 -› 14N + 14C 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
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.
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.
