Tracing Evolutionary History Flashcards
What made the origin of life possible?
Conditions on early Earth - The Earth formed about 4.6 billion years ago
What was most likely in the first atmosphere?
The first atmosphere was probably thick with water vapor and various compounds released by volcanic eruptions, including nitrogen and its oxides, carbon dioxide, methane, ammonia, hydrogen, and hydrogen sulfide
Where does the earliest evidence for life on Earth come from?
It comes from 3.5-billion-year-old fossils of stromatolites, build by the ancient photosynthetic prokaryotes still alive today - these prokaryotes suggest that life first evolved earlier, perhaps as much as 3.9 billion years ago
Where did bacteria come from?
Bacteria evolved ~3.5 billion years ago
Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages
1. Abiotic synthesis of small organic molecules
2. Joining of these small molecules into polymers
3. Packaging of molecules into “protobionts”
4. Origin of self-replicating molecules
What did Russian chemist A. I. Oparin and British scientist J. B. S. Haldane propose in the 1920s?
They independently proposed that the conditions on early Earth could have generated organic molecules
What id Stanley Millers 1953 experiment show?
It tested the Oparin-Haldane hypothesis and showed that the abiotic synthesis of organic molecules is possible
What organic molecules did Miller identify were common in organisms?
Hydrocarbons (long chains of carbon and hydrogen) and some of the amino acids that make up proteins
What was demonstrated to be possible by the Miller experiments?
Stage 1 abiotic synthesis of organic molecules
Where is another place that organic compounds may have been synthesized?
Instead of forming in the atmosphere, the first organic compounds may have been synthesized near submerged volcanoes and deep-sea vents
Protocells
A collection of organic molecules within a membrane-enclosed compartment
What did laboratory experiments demonstrate about lipids and water?
They demonstrated that small membrane-bounded sacs or vesicles form when lipids are mixed with water
What do vesicles exhibit?
They exhibit simple growth, reproduction, and metabolism
They can absorb organic molecules attached to montmorillonite particles through a selectively permeable bilayer
What is the origin of self-replicating molecules?
Today’s cells transfer genetic information from DNA to RNA to protein assembly. However, RNA molecules can assemble spontaneously from RNA monomers
What happens when RNA is added to a solution containing a supply of RNA monomers?
New RNA molecules complementary to parts of the starting RNA sometimes assemble
Ribozymes
An RNA molecule, can carry out enzyme-like functions, and may have facilitated RNA replication
What was probably the first genetic material?
The first genetic material was probably RNA, not DNA
If a vesicle on early Earth could grow, split, and pass on its RNA to its “daughter” what would its daughter be?
Protocells
What is Deinococcus radiodurans?
An extremophile bacterium- can survive cold, dehydration, vacuum, and acid
Means that life might have arrived on earth in/on meteorites
Sedimentary rocks
Deposited into layers called strata and are the richest source of fossils
What does the fossil record show?
It shows changes in the kinds of organisms on Earth over time
What is the fossil recored biased in favor of?
Existed for a long time, were abundant and widespread, and/or had hard parts such as shells or skeletons
What does the sedimentary strata reveal?
It only reveals relative ages
What can absolute dating be determined by?
It can be determined by radiometric dating
What does a “parent” isotope decay into?
It decays into a “daughter” isotope at a constant rate
Half-life
The time required for half the parent isotope to decay
What is Carbon-14 useful for?
Dating relatively young fossils - up to about 75,000 years old
What can the age of some fossils be estimated by?
Measuring the ratio of the radioactive isotope carbon-14 to the stable isotope carbon-12
What are radioactive isotopes with longer half-lives used for?
They are used to date older fossils
The geologic record
Divided into the Hadean, Archaean, Proterozoic, and Phanerozoic eons
What three eras is the Phanerozoic divided into?
The Paleozoic, Mesozoic, and Cenozoic
What do major boundaries between eras correspond to?
Major extinction events in the fossil record
The Anthropocene
A period during which human activity has been the dominant influence on climate and the environment
What was the first single-celled organisms?
Prokaryotes were Earth’s sole inhabitants from 3.5 to about 2 billion years ago
Stromatolites
The oldest known fossils that date back 3.5 billion years ago - rocklike structures composed of many layers of bacteria and sediment
Did the earliest types of photosynthesis produce oxygen?
No it did not
When did oxygenic photosynthesis probably evolve?
About 3.0 billion years ago in cyanobacteria
Banded Iron Formations
Formed by the rise in O2 causing dissolved Fe to oxidize “rust”
What did the Oxygen revolution do to life on Earth?
It posed a challenge for life
- was poison for many organisms
- allowed ionized forms (hydrogen peroxide and super oxide) to be able to attack proteins and nucleic acids
-Provided opportunity for evolution of cellular respiration
-Allowed organisms to exploit new ecosystems
Eukaryotic cells
Date back 1.8 billion years
Eukaryotic cells have a nuclear envelope, mitochondria, endoplasmic reticulum, and a cytoskeleton
Endosymbiosis
When a prokaryotic cell engulfed a small cell that would evolve into a mitochondrion
What is an endosymbiont?
A cell that lives within a host cell
Do all eukaryotes have mitochondria and plastids?
No, all eukaryotes have mitochondria or remnants of mitochondria, but not all have plastids
Serial endosymbiosis
Supposes that mitochondria evolved before plastids through a sequence of endosymbiotic events
Karyogenic hypothesis
Invagination of cell membrane compartmentalized DNA
Endokaryotic hypothesis
The nucleus is a result of an endosymbiotic event
- Probably an archaeon because nuclear-associated functional genes are more closely related to archaeal genes
- Cytoplasmic genes are more closely related to bacterial genes
What evidence supports the Endosymbiotic theory?
- Mitochondria and plastids formed by process similar to binary fission
- Mitochondria and plastids cannot be formed de novo
- Inner membranes of both organelles are similar to plasma membranes of living bacteria
- Have their own genome, DNA is circular and similar to bacteria
- No histones
- Both organelles transcribe and translate their own DNA
- Possess different protein synthetic machinery and ribosomes resemble prokaryotic
- Many antibiotics inhibit mitochondrial protein synthesis
What would anaerobic host cells have benefited from?
They would have benefited from endosymbionts that could use oxygen as it built up in the atmosphere
The Cambrian Explosion
Refers to the sudden appearance of fossils resembling modern animal phyla in the Cambrian period (535 to 525 million years ago)
What were the fist organisms to start colonizing land?
- Fungi and plants began to colonize land about 500 million years ago
- Arthropods on land 450 mya
- Tetrapods on land 374 mya
What played a major role in macroevolution?
Continental drift
What does the theory of plate tectonics state?
According to the theory of plate tectonics, the Earth’s crust is divided into giant, irregularly shaped plates that essentially float on the underlying mantle
What did plate movement bring about 250 mya?
- Plate movements brought all the landmasses together and the supercontinent of Pangaea was formed
- Started to separate in Mesozoic
- Biological diversity was reshaped during these episodes
Scott’s ‘failed’ Antarctic expedition 1912
His party hauled 35 Lb of plant fossils back from the S. Pole.
Was conclusive evidence that ancient lunch deciduous forests had carpeted the continent 250 million years previously
What can separation of landmasses lead to?
Allopatric speciation
What does the distribution of fossils and living groups reflect?
The historic movement of continents
What does the rise and fall of groups of organisms reflect?
It reflects differences in speciation and extinction rates
Is extinction inevitable in a changing world?
Yes
How many mass extinctions have occurred over the last 500 million years?
Five mass extinctions have occurred and in each event, more than 50% of the Earth’s species went extinct
Permian mass extinction (252 mya)
This mass extinction occurred in less than 500,000 years and caused the extinction of about 96% of marine animal species
What are some events that might have caused the Permian mass extinction?
- Extreme volcanism in what is now Siberia might have contributed to this mass extinction
- Global warming and ocean acidification resulting from the emission of large amounts of CO2 from volcanoes
- Anoxic conditions resulting from nutrient enrichment of ecosystems
Cretaceous mass extinction (65 mya)
By end of Cretaceous, dinosaurs were extinct
- A few species may have survived into the early Cenozoic
- Dinosaurs may have been in decline before the asteroid impact near Yucatan Peninsula
Adaptive radiation
The rapid evolution of diversely adapted species from a common ancestor
Adaptive radiation may follow
- mass extinction / removal of competition / predators
- the evolution of novel characteristics / adaptations
- specialization
- the colonization of new regions
When did mammals undergo an adaptive radiation?
After the extinction of terrestrial dinosaurs
What did the disappearance of dinosaurs (except birds) open?
It opened ecological niches, allowing for the expansion of mammals in diversity and size
Regional adaptive radiations
Adaptive radiations can occur when organisms colonize new environments with little competition
