GEOL 107: Important terms and definitions

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Principle of superposition

Principle of superposition

Oldest rocks are at the bottom (deposited first) and youngest are at the top (deposited last)

Law of Original Horizontality

Rock strata are deposited in horizontal layers that are parallel with each other

Law of Original Continuity

Rock strata are deposited in layers that are continuous over lateral distance

Geological Time Scale

Subdivision of geologic time using divisions based on their fossil content (biostratigraphy), applicable worldwide

Biota of Cenozoic era

• Acme of mammals, birds, and flowering plants

• Hominids appear late in this era

Biota of Mesozoic era

• Age of dinosaurs

• Ammonites, ichthyosaurs and pleisiosaurs in the seas

Biota of Paleozoic era

• Age of trilobites, brachiopods and other archaic invertebrates in the seas

• First land plants, amphibians and reptiles occur late in this era

Advantage of absolute dating

Radioactive decay provides the best indication of absolute age

Can be dated with C-14 dating

organic fossils <60,000 years old (not useful for older fossils)

Can be dated with U/Pb dating of zircons

Fossils that are older than 60,000 years old are commonly dated indirectly by dating radioactive minerals in igneous rocks above and below the fossil

Theory proposed by Alfred Wegener in 1912

Continental Drift

Definition of plate tectonics

1. Continents are moving (at speeds that can be measured by satellites)

2. Oceans are some of the youngest features on this planet, are constantly being created and destroyed

3. Mountains are the records of ancient collisions of plates

Evidence for continental drift as proposed by Wegener

1. ‘Fit’ of the continents, especially east South America and west Africa

2. Distributions of Late Paleozoic and Early Mesozoic fossils through South America, Africa, India, Antarctica, and Australia suggesting that they were combined into the megacontinent Gondwana

3. Consistent ice-flow directions away from the center of Gondwana

4. Continuation of mountain belts across present ocean basins

New evidence for continental drift (1960s)

1. Mid-ocean ridge down the center of the Atlantic also perfectly matches the ‘fit’ of the

   continents

2. No ocean crust older than about 180 Ma (Jurassic) anywhere on Earth. Ocean crust gets progressively older away from the mid-ocean ridge

3. New field of paleomagnetics (not discussed in this course) used magnetic directions recorded in rocks to determine the latitude at which the rocks were formed, showing that continents are and have been moving

Last 3 supercontinents on Earth in the last billion years (in order)

Nuna (~2000 Ma), Rodinia (1200-800Ma) and Pangea (300-200Ma, Carboniferous - Triassic)

3 stages of continent breakup

1. Rift valley

2. Linear sea

3. Ocean

DNA

Genetic information of an individual, coded as a series of nucleotides

Gene pool

Total amount of genetic information coded on all the individuals in the population

Effect of sexual reproduction on gene pool

Constantly reshuffle the gene pool into different individuals

Mutation

Change in one or more nucleotides on the DNA

Natural selection

The proportion of a beneficial mutation in a population can be enhanced, causes “survival of the fittest” (competition for food, living space and mates + avoidance of predators)

Directionality of natural selection

Enhances ‘beneficial’ genes and reduces or eliminates ‘harmful’ ones in a population

Convergence (aka convergent evolution)

Similar life habit in a similar environment leads to the evolution of similar morphology among organisms that are completely unrelated

Analogous structures

Structures that are a result of convergent evolution (Example is wings: been evolved separately by insects, birds and bats)

Coevolution

Organisms evolve as a response to changes in their environment, but also in response to evolutionary changes in other organisms

“Arms race” between predator and prey

• Carnivore vs prey animals (i.e speed, power, or complex hunting strategies for predator, prey may evolve increased speed, camouflage, armour, poisons and other noxious deterrents etc.)

• Herbivores vs plants (adaptations by the plant may include spines or poisons)

Mutualism

Relationship between two species that is beneficial to both (i.e co-evolution of flowering plants and animals)

Red Queen Effect (from Van Valen, Evolutionary Theory, 1973)

Any evolutionary advance by one species forces the rapid evolution of all species that are dependent on it. There is no staus quo in evolution; all species must constantly evolve or they will go extinct

Court Jester Effect (from Barnosky, Journal of Vertebrate Paleontology, 2001)

Life is also affected by major physical perturbations in the Earth System (e.g., climate change, widespread volcanism, large meteorite impacts), these suddenly change the rules on the biotic playing field and can result in an accelerated evolutionary response

Number of living species

Approximately 2 million

Number of living animal species

Approximately 1,000,000

Phylogeny

Biological classification of organisms must reflect evolutionary history

Prokaryotes

Unicellular, lack a cell nucleus or organelles (e.g. plastids, mitochondria)

Eukaryotes

Unicellular or multicellular, DNA in a nucleus, contain organelles

3 domains of life

1. Bacteria

2. Archaea

3. Eukarya

Bacteria

Mostly “normal” prokaryotes

Archaea

Mostly “extremophile” prokaryotes

Eukarya

Includes all single and multi-celled eukaryotes

Levels of Linnean classification (largest to smallest)

1. Kingdom

2. Phylum

3. Class

4. Order

5. Family

6. Genus

7. Species

Cladistics

Investigation of morphology to recognize clades

Clade

A monophyletic group (common ancestor and all its descendents)

Polyphyletic

more than one ancestor (e.g. “corals” which evolved separately from different anemone groups)

Paraphyletic

Common ancestor but does not include all descendants (e.g. “reptiles” have a single common ancestor but do not include birds or mammals which are also their descendants)

Basal morphological characters

Relating to original ancestoral features, aka pleisiomorphies

Derived morphological characters

First appear in the clade, aka apomorphies

Analogous/convergent morphological characters

Similar features in unrelated organisms

Cladogram

Shows the order of evolutionary appearance of derived characters

3 Strengths of cladistics

1. Rigorous and testable

2. Can be used at almost any level of taxonomy

3. Can include fossil and living species in the same cladogram

Phylogenetics (aka molecular phylogeny)

Measures degree of substitution in DNA, RNA or proteins (directly measures genetic differences!)

Molecular clocks (result of phylogenetics)

Provide a "ruler" to measure the time of origin of different clades

3 Strengths and 1 weakness of molecular phylogeny

Strengths:

1. Rigorous and testable

2. Can be used at any level of taxonomy (from kingdoms to populations within the same species)

3. Directly measures genetic differences

Weakness:

1. With rare exceptions (e.g. fossils in amber) can only be used on modern organisms

Fossils

The remains of ancient organisms (can include the actual remains themselves (e.g. shells and bones) or features made by them (e.g. footprints and burrows))

5 categories of fossils

1. Bones (vertebrates)

2. Shells (invertebrates)

3. Cellulose (plants)

4. Trace fossils

5. Soft tissue

Taphonomy

Conditions of fossilization

Composition of bone fossils

Phosphate (more resistant to weathering)

Formation of complete skeleton fossils

Animal must be buried rapidly during or immediately after death

Composition of shell fossils

Carbonate (calcite or aragonite), sometimes composed of silica or even phosphate

Molds

Impressions of shell fossils left in rock

Composition of cellulose fossils

Complex sugar (cellulose)

How petrified wood forms

Wood pores are filled with silica (quartz)

Carbonization

Cellulose buried more than a few hundred metres deep turns into coal due to heat and pressure

Types of trace fossils

Includes tracks, trails, burrows, and borings of animals (vertebrates and invertebrates)

Important things trace fossils tell us

• Behaviour of the animal that made them

• What type of animal made them

• Speed the animal was travelling at the time

What usually happens to soft tissue after death

Decomposes soon after death and is not preserved as a fossil

Fossil Lagerstätten

Deposits of fossils with preserved soft tissues

Ways that fossil Lagerstätten can be made

• Freezing in ice

• Mummification

• Petrification in amber

• Carbonization

• Mineralization

Late Heavy Bombardment

A second wave of major impacts that would have sterilized the upper oceans

Faint Young Sun

Sun only 75% as bright as it is today during the Early Archaean

Early Archaean atmosphere composition

Volcanic atmosphere (H2O, CO2, SO2, N2) with absolutely no free oxygen!

Appearance of Archean Earth

Many volcanic islands but no true continents

3 Steps in the synthesis of life

1. Formation of Simple Organic Molecules (Amino Acids, Nucleotides, Sugars)

2. Combination of Simple Organic Molecules into Complex Organic Molecules (DNA,

   RNA, Proteins)

3. Initiation of Replication (Reproduction)

Why DNA cannot have been the first complex organic molecule synthesized

Its formation requires proteins

Miller-Urey Experiment

Showed that volcanic gases + spark → all amino acids essential to life, and that this reaction always works if anoxic; reaction never works if any oxygen is present

2 competing models for early life

1. proteinworld

2. RNA-world

Why RNA-world is favoured

RNA can both replicate itself (like DNA) and act as a catalyst in reactions (like proteins)

“Spiegelman Monster” experiment

Showed that self-replicating living systems can consist of little more than a short strand of RNA

Eigen experiment

Same as “Spiegelman Monster” experiment but got the same results without providing a living organism as a seed

Where life is descended from

All life on Earth appears to have descended from a single common ancestor

How comets and meteorites may have contributed to life

By striking the Earth and (maybe!) contributing large amounts of these fundamental building blocks of life

Where life probably started

Extremophiles (Archaea) in hydrothermal systems (e.g. mid-ocean ridges, vents, and caldera)

The 2 locations of Earth’s oldest definite fossils

1. Pilbara Craton of Western Australia (the most famous is Warrawoona at 3.5 Ga)

2. Barberton in South Africa (3.4 Ga)

Organic microfossils

Filaments and spheres of carbon that reflect the cell walls of unicellular organisms

Specific fossils found at Warrawoona (3.5 Ga) in the Pilbara craton of Western Australia

1. Oldest-known organic microfossils (3.5 Ga)

2. Filamentous microfossils 3.25 Ga from nearby Sulphur Springs

3. Oldest definite stromatolites (3.5 Ga)

Specific fossils found at Barberton

1. Ancient spherical microfossils (3.4 Ga)

2. Microbial mats that still contain carbon (3.2 Ga rocks)