4.4 Fossils and the History of Life Flashcards
Fossil
Preserved remains of an organism, or an impression, trace, or track of that organism
Typically mineralized tissues (bones, teeth, shells, exoskeletons)
Soft tissues under the right conditions
Most dead organisms don’t fossilize
Permineralization
Most common method of fossil formation
Dissolved minerals in groundwater permeate soft tissues, then crystallize, to form rock that is shaped like the organism. Hard tissues are left behind.
Replacement
Similar to permineralization, except that hard tissues are dissolved and replaced by minerals
Compression
Heat and pressure cause the release of hydrogen and oxygen from the remains of an organism, leaving behind only a thin layer of carbon residue.
Occurs more often with plants than animals
Encasement
Entire body of organism can be preserved if frozen, dried, or trapped in tar or resin that hardens into amber.
Soft tissues still degrade and decompose
Impression (casts and molds)
Rigid outer surface of an organism can form an imprint in sediment as it decomposes
Internal molds can form if the specimen is hollow
Trace fossils
An organism moving over soft sediment leaves tracks or trails which are preserved if the sediment hardens or is covered by another layer
Molecular fossils
Organic molecules left behind by an organism
Most can be found in kerogen
Kerogen
Solid, water-insoluble organic matter embedded in roc
Chemical fossils
Traces of organic chemicals that indicate former life
Relative dating
Estimates age of a feature based on the other layers around it
Absolute dating
Uses quantitative, lab-based techniques to determine age of an object or feature
Typically focus on radioactive elements or changes in Earth’s magnetic field
Index fossils
From organisms known to have lived in a specific time period and in many places
Law of superposition
Lower strata are older than the layers deposited on top of them
Cross-cutting relationships
Geological principle stating that the geological feature that intrudes into another is younger than the feature it intrudes into
Biostratigraphy
Branch of science that uses index fossils to understand the relative ages of rock layers from different geographic regions
Principle of faunal succession
Principle that fossil species appear and disappear from individual layers in a certain order and that extinct species don’t reappear in younger layers of rock
Radiometric dating
Based on decay of radioactive isotopes of elements
Paleomagnetism
Measures changes in the magnetic field of the Earth
Magnetic minerals in newly formed volcanic deposits orient towards the Earth’s magnetic field as they cool
Isotopes
Different forms of the same elements that have different number of neutrons
Some are unstable and undergo radioactive decay
Radioactive decay
Ejecting matter and energy from their nuclei to reach a stable state
Occurs at a constant rate and can be used to determine age of materials
Half-life
Length of time it takes for half of the radioactive elements in sample to decay
Carbon-14
Used in radio metric dating, decays into Nitrogen-14
Half-life of 5,730 years
Useful for dating organic materials formed within the past 70,000 years
Potassium-40
Decays into 40Ar
Useful for dating rocks and minerals 1,000 to billions of years
Uranium-234
Decays into 40Ar
Useful for dating rocks and minerals 1,000 to billions of years
Ecological time
Used to discuss how an environment changes over time and how that influences the species in that environment
Geologic time
Considers the entire history of the earth
Begins with formation of earth about four to five billion years ago
Divided into eons, eras, periods, and epochs
Eons
Largest unit of geologic time
Hadean, Archean, Proterozoic, Phanerozoic
Phanerozoic
Current eon beginning 542 million years
Precambrian Super Eon
Hadean, Archean, and Proterozoic Eons
Hadean Eon
No life on earth
4.6-4 billion years ago
Earth still forming
No solid crust until 4.3 or 4.4 billion years ago (evidenced by zirconium crystals in Western Australia)
Oceans did not exist (water vaporized)
Not divided into eras or smaller geologic times
Archean
Formation of earliest rocks (granite) marked the start of this eon
4-2.5 billion years ago
Earth’s crust cooled enough to form continents and oceans
Large amount of volcanic activity
Atmosphere lacked oxygen
Earliest evidence of life
3.7 billion year old rocks in Greenland containing graphite created through biological process
Earliest fossils
3.5 BYO microbial mats formed by Cyanobacteria
Earliest evidence of bacterial life on land
3.2 BYA
Neoarchean
Final era of Archean eon
About 2.8 BYA microorganisms started releasing oxygen molecules into air as byproduct of photosynthesis, making evolution of aerobic life possible
Proterozoic
Evolution of photosynthetic Cyanobacteria marks beginning of this eon
Began 2.5 BYA-541 MYA
Glaciers first formed
Entire surface of the Earth may have frozen at some point during this eon
Oxygen crisis occurred
Origin of nucleus and endoplasmic reticulum
Origin of mitochondria and chloroplasts 2.1-1.6 BYA
True multicellular organisms arose during end of this eon
Oxygen Crisis
AKA Great Oxidation Event
During the Proterozoic eon
About 2.4-2.0 BYA atmospheric oxygen levels significantly increased
Extinction of enormous numbers of anaerobic microorganisms
Phanerozoic
Initiated by the Cambrian Explosion about 541 MYA
Appearance of trilobites and corals marks boundary between this eon and the Proterozoic eon
Appearance of and plants, insects, fish, tetrapods
Tectonic plates formed Pangea which broke up later in the eon
Cambrian explosion
Event of evolutionary radiation occurring over about 20 million years
Resulted in evolution of most animal phyla
Era
Unit of geologic time spanning about one hundred million to a few hundred million years
Phanerozoic eras
Paleozoic, Mesozoic, Cenozoic
Paleozoic
Era occurring 541-251 million years ago
Aquatic invertebrates, mollusks, arthropods, fish, amphibians, and reptiles diversified with transition from aquatic to terrestrial environments aided by evolution of land plants
Massive conifer forests covered planet allowing evolution of gigantic insects in an oxygen rich environment
Ended with the catastrophic Permian extinction
Permian extinction
Volcanic activity in Siberia wiped out around 90 percent of species at the end of the Paleozoic era
Mesozoic
AKA “Age of the Reptiles”
Further increase in biodiversity
Appearance of dinosaurs, small mammals, birds, and flowering plants
Pangea began to slowly split apart
Temperatures were variable and higher than present day
Ended with a mass extinction
Climate hot and humid, forests found at the poles, sea levels higher
Cenozoic
Era occurring 66 MYA to present
Mammals diversified
Continents moved to current positions
Climate dried and cooled around time the Himalayan mountains formed due to exposed rock reacting with CO2 in air, reducing greenhouse gases
Continued cooling caused a series of glacial and interglacial periods (ice ages)
Most recent ice age
115,000 - 11,700 years ago
Period
Span tens of millions of years
Tertiary period
Used to collectively refer to the Paleocene and Neogene periods
Paleozoic periods
Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian
Cambrian
Period of the Paleozoic era starting 541 MYA
Warming climate
Diversification of many invertebrates
Biofilms and microbial mats
Trilobites
Earliest vertebrates
Ordovician
Period of the Paleozoic era starting 488 MYA
Warming climate before later cooling and glaciation
Evolution of fishes
Filter feeders and marine invertebrates
First terrestrial plants
Silurian
Period of the Paleozoic era starting 443 MYA
Stable, warm temperatures
Vascular plants
Moss forests
Terrestrial invertebrates
Bony fish
Devonian
Period of the Paleozoic era starting 416 MYA
Warm temperatures
First seed-bearing plants
Diversification of fish
Placoderms rule the sea
Earliest insects
Carboniferous
Period of the Paleozoic era starting 416 MYA
Warm temperatures
First seed-bearing plants
Diversification of fish
Placoderms rule the sea
Earliest insects
Permian
Period of the Paleozoic era starting 299 MYA
Formation of Pangea
Variable climate with warm and cool cycles, relatively drier
Diversification of amniotes into mammals and reptiles
Reemergence of corals after large extinction
End of Permian marked by worst mass extinction in history
Mesozoic periods
Triassic, Jurassic, Cretaceous
Triassic
Period of the Mesozoic era starting 251 MYA
Warm and dry with seasons
Diversity recovered by mid-period
First mammals, dinosaurs, and crocodiles
Evolution of lichens
Conifer forests dominant
Jurassic
Period of the Mesozoic era starting 200 MYA
Breakup of Pangea
Conifers and cycads (palm trees) abundant
Larger, iconic dinosaurs
First birds (Archaeopteryx)
Cretaceous
Period of the Mesozoic era starting 146 MYA
Relatively warm, humid climate
Many shallow inland seas
Spread of flowering plants
Dinosaurs at peak diversity
Insects diversifying
Radiation of diatoms
Cenozoic eras
Paleogene, Neogene, Quaternary
Paleogene
Period of the Cenozoic era starting 66 MYA
Warm temperatures shifting to a cooler climate
Diversification of mammals
Adaptive radiation of birds
Increase in grasses
Decline in tropical plants
Neogene
Period of the Cenozoic era starting 23 MYA
Seasonal climate
Cooling and drying
Evolution of mammals and birds into modern forms
Increase in grasslands
Quaternary
Period of the Cenozoic era starting 2.6 MYA
Cycles of glaciation and ice sheet formation
Large mammals
Evolution of humans and their culture
Epoch
Last about 5-20 million years
Paleogene epochs
Paleocene, Eocene, Oligocene
Paleocene
Epoch of the Paleogene Period starting 66 MYA
Subtropical/tropical climate
Temperate poles
Diversification of mammals
Eocene
Epoch of the Paleogene Period starting 56 MYA
Maximum temperature reached for Cenozoic before cooling
Placental mammals
First prosimians (primates)
Oligocene
Epoch of the Paleogene Period starting 33.9 MYA
Antarctic ice sheet formed
Increase in open landscapes
Mass extinction that replaced many European species with Asian ones
Miocene
Epoch of the Neogene period starting 23 MYA
Continued cooling
Expansion of grasslands and plains
First apes
Piocene
Epoch of the Neogene period starting 5.3 MYA
Continued cooling (2-3°C warmer than today)
Elevational changes
Formation of land bridge between Alaska and Siberia
First bipedal hominids
Pleistocene
Epoch of the Quaternary period starting 2.6 MYA
“Ice Age”
Arctic ice cap formed
Cyclical glaciation
Large mammals such as mammoths, mastodons, and giant sloths
First modern humans
Extinction of Neanderthals
Formation of Yellowstone caldera (the most recent eruption of the Yellowstone super volcano was 630,000 years ago)
Holocene
Epoch of the Quaternary period starting 11,000 years ago
Began with the last retreat of the glaciers; expansion of modern humans
Some critics argue that it is arbitrarily defined since it continues the cycles of glacial and interglacial periods typical during the Pleistocene
Anthropocene
This existence of this epoch is debated within the scientific community
Characterized by human-mediated changes to the Earth
Would have begun post-WWII during the Atomic age
Demarcated by an increase in carbon dioxide and dusting of abnormal radioisotopes across the planet
Phyletic gradualism
Postulates that speciation occurs at constant rate, slowly/gradually over time
No differentiation between ancestor and descendants unless two different species evolve from one
Punctuated equilibrium
Several descendant species quickly arise from single ancestor at roughly same point in geologic time due to:
Sudden break-up of populations
Exploitation of different niches
Mass extinctions
Biotic potential
Max capacity of an organism to reproduce under ideal environmental conditions
Coevolution
Two or more species are interdependent in ways that affect each other’s evolution such as:
- Predators and their prey
- Plants and herbivores
- Hosts and parasites
- Flowering plants and pollinators
Homeostasis
Ability to maintain a constant state of internal conditions that differs from the outside environment
Origin of life
Scientists agree that life originated through abiogenesis
Most scientists believe that life spontaneously arose from a primordial soup
Disagreement about whether life arose near the ocean’s edge, in hydrothermal vents deep in the sea, far beneath Earth’s crust, or somewhere else
Debate about exact composition of the atmosphere and oceans
Primordial soup
Hot water, carbon dioxide, methane, ammonia, hydrogen sulfide, hydrocarbons, and other simple molecules
Alexander Oparin and J.B.S. Haldane
Developed theory of origin of life from a primordial soup in the 1920s
Reducing atmosphere
Atmosphere in which oxidation can’t take place
Panspermia
Theory postulating that the precursor molecules for life or life itself may not have originated on earth at all but from meteors carrying organic molecules
Could have worked alongside other ongoing processes on ancient earth
Abiogenesis
Life originating from nonliving materials
Stanley L. Miller and Harold C. Urey
Miller-Urey experiment in 1953 simulated hypothetical conditions of early Earth
Wanted to determine what if any organic molecules may have existed
Boiling water placed below a reducing atmosphere consisting of water vapor, carbon dioxide, methane, ammonia, and hydrogen gas
Sparking electrodes where positioned in the simulated atmosphere to create “lightning”
Water vapor would rise from the ocean, pass through the atmosphere, condense and return to the ocean
Repetition of this cycle created formaldehyde (CH2O), hydrogen cyanide (HCN), formic acid (HCOOH), urea (CO(NH2)2) as well as the amino acids glycine, alanine, and aspartic acid
Recreations of this experiment have found that other amino acids as well as adenine could be generated under these conditions
Protocells
Bubble of lipids containing inorganic and organic molecules at higher concentrations than the external environment
Coacervate
Earliest protocells
Microdroplets of lipids and amino acids or nucleic acids suspended in aqueous solutions
Not alive
Accumulated molecular material
Reproduced through fragmentation
RNA world
Hypothesis based on the dual function of RNA in storing genetic information and catalyzing enzymatic reactions
RNA molecule would be capable of creating a duplicate of itself
Over time RNA molecules would have begun interacting with amino acids in the primordial soup creating polypeptides and eventually a ribosome
These molecules could have been gathered by protocells and served as a precursor to life
Evolution of eukaryotic cells
Evolved form prokaryotic cells about 2.1 billion years ago as a chimera of a host cell and an alpha-proteobacterium in endosymbiosis, evident by
Mitochondria possess own circular genome, ribosomes, and tRNAs resembling prokaryotes
Mitochondrial genes for respiration (though sometimes relocated to eukaryotic genome) are very similar in sequence to genes of alpha-proteobacteria
Mitochondria is surrounded by two membranes (as if drawn in through vacuole)
New mitochondria produced through process similar to binary fission
Eukaryotic cells cannot make their own mitochondria from scratch
Not clear whether the endosymbiotic event that led to mitochondria happened before or after proto-eukaryotic cells developed nuclei
Endosymbiosis
One cell lives inside another cell and both cells benefit from the relationship
Origin of plastids
Endosymbiosis between a eukaryotic cell and cyanobacterium
LECA
Last eukaryotic common ancestor
Contains mitochondria, cytoskeleton, made of microtubules and filaments, and a nucleus surrounded by a nuclear envelope with nuclear pores
May have lacked cell walls
