BIOL360 Study Guide - Midterm Guide: Bivalve Shell, Bioerosion, Aragonite

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5 Aug 2016
Biology 360: Evolution 2 The Fossil Record
midterm review
General Introduction to Paleontology
Geological time scale: divided into a hierarchy of units: Eras, Periods, and Epochs
Paleontology: study of life in the past through use of fossils or any other clue of past existence
oPaleontologist = forensic scientist
oFossil: remains of any ancient organism
oUse of fossils to piece together the organism to determine how it may lived, where, and under what
The activity of organisms can be fossilized as well e.g. worm burrows
Why care about paleontology?
To determine origins of organisms
To discover different worlds of organisms: worlds of only microbes where there was 10x more 02, lizard
To track changes in climate and biodiversity, predict future events by understanding the past
Evolution: all species are related to each other, i.e. tree of life
Extinction: no species last forever
Age dating: use of fossils to date rock; industrial geology
Fossils and Evolution
In the early 1800s, only a few fossils were known
Progressionism and evolution: simplest life forms in oldest rocks progressed to more complex ones in
older rocks
Darwinian evolution: Darwin developed evolution by natural selection: considerable variation in life
forms, and no fixed type of alleles/genes. Surviving individuals adapted to do so, and these adaptations
would be inherited
Paleontology today
The 1800s were a great time of exploration and discovery
Darwin’s missing link: late 1870s, Archaeopterix, which was the first bird. Darwin predicted birds linked to
dinosaurs and hoped that fossil evidence would support his ideas of evolution
The first dinosaur craze in England in the 1850s was fueled by new discoveries and dramatic new
reconstructions of the ancient inhabitants of that country. Thought that dinosaurs were mammal-like
Archaeopteryx; Jurassic
oFull set of teeth, rather flat sternum “breastbone”, long & bony tail, gastralia (“belly ribs”), three claws
on the wing which could have still been used to grasp prey and trees, feathers, wings, furcula
(“wishbone”) and reduced fingers – like modern birds
oHuman fossils were being discovered around this time too
oEarly humans – Homo erectus (1895); ideas of human evolution in 1924 with Australopithicus
oEarliest life forms: Cambrian to Burgess Shale of western Canada in 1830s; Ediacarians in 1947 and
simpler life in 1960s; great strides in recent decades to understand these earliest life forms
Fossils and Taphonomy
Taphonomy: the study of what happens to an organism after its death and until its discovery as a fossil
Lithostratigraphy: the study of strata/rock layers (units recognized as basis of rock types) and how they
are formed
oSedimentary rocks usually contain fossils
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Biostratigraphy: study that focuses on determining relative ages of strata by using fossil assemblages
within them
oThe use of fossils in dating rocks. Indicator fossils: local vs regional scales
Zone fossils: correlate rocks based on biostratigraphy
oFacies fossils: indicator fossils used to track a particular environment over a long period of time
oZone fossils: widespread indicator fossils used for short time intervals
How do we know the age of a fossil?
oRelative time scale: places geological events/rocks in time order relative to other rocks
e.g. fossil A is older than fossil B (if fossil B is on top of fossil A)
oAbsolute geological ages: assigns rocks date or date range in terms of years through radioactive
Fossil skulls cannot be dated because they do not contain radioactive isotopes; however, the ash
layers can be dated via absolute dating. Volcanic ashes have special characteristics – valuable
dating technique
E.g. It takes 1.3 billion years for half of potassium-40 to break down to argon-40, then measure
the amount of radioactive decay that is trapped inside nearby crystals/rock
Radiocarbon dating: ratio of carbon 12 to carbon 14 is the same in all living organisms, so once an
organisms has died, the time since their death can be determined by comparing the ratio of
carbon 12 to carbon 14. The oldest dates that can be reliably measured are 50, 000 years ago
from Quaternary time
Paleobiogeography: geographic distribution of fossils – all living organisms have a defined geographic
oDarwin recognized biogeographic realms (8 today). Realms are defined by endemic species that are
restricted to a certain area and cosmopolitan species that have a wide-range distribution.
Biogeographic provinces have changed positions given that continents have overtime. Fossils
indicated continental drift also.
Fossil: remnant of an organism preserved in the geological record
oOrganisms can be destroyed/damaged before they become fossils or while they are fossils
oSoft parts can decomposed and hard parts can dissolve, break, crush, or be scattered
oSmall organisms are easier to be preserved on ocean floor/lakes/wetlands than on land
oFossil represents a biased sample of ancient life
oNegative evidence: non-occurrence or absence of something – does not mean it was never there
Most organisms do not end up as a fossil
Study of processes that occur: after death of an organism, during decomposition, before its fossilization
oFactors: predation, dessication (extreme drying out), transport by wind or water
Types of fossils
Body fossils: all or part of an organism is preserved
oE.g. brachiopod: original calcite shell replaced by silica. Frog preserved in amber, covered by resin
o2D compressions made, mostly for plants. Organic materials are retained and are chemically
unaltered. Provide information on the cellular structure of the organism and the external morphology
Trace fossils: not part of the organism, but is produced by the organism e.g. footprints, trails, burrows
oImpressions can be made, 2D but contain no organic material
Chemical fossils: compounds produced by organisms and preserved in the rock record
Fossilization Process
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Fossil Preservation
Decay: mineralization, scavenging (e.g. meat-eating beetles, hyenas), temperature and pH (i.e. bog
oAerobic decay: microbial break-down of organic carbon
oAnaerobic decay: such as sulfate decay, iron oxide
oNature of the organic carbon, i.e. labile (soft animal parts, easily broken down) vs refractory carbon
(lignin in plants, retains its strength even under high temperatures/conditions)
Fossil record is biased for organisms with hard parts, in some marine environments, 60% of organisms
are soft-bodied. Fossils are mostly hard parts
oShells: calcium carbonate can be recrystallized to form aragonite calcite (mineralization)
oSponges, radiolara: silica
oBones: phosphate/apatite
oPlants: lignin, cellulose
Decay: quality of preservation depends on how soon decaying stops after death
oMineralization: inorganic material replaced with minerals/organic materials
oPetrification: organic material replaced with minerals/organic materials
Decay is controlled by:
oAmount of oxygen: aerobic breakdown of carbon
oTemperature and pH
oNature of organic C: volatile has fast decay, refractory has slow decomposition
Exceptional preservation: Lagerstatten = storage place in German
oExceptionally well-preserved and wide variety of many fossils, often with soft parts, found in one place
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