Chapter 25 Pt II: The History of Life on Earth Flashcards
In which type of rock are fossils typically preserved?
Sedimentary
What types of organisms are less likely to be preserved as fossils?
rare, short-lived, without any hard parts
What are strata?
layers of sedimentary rock which indicate age
How can fossil age be estimated?
location in strata and/or radiometric dating
How is radiometric dating done?
by measuring decay of radioactive isotopes
What are macroevolutionary changes?
important milestones in the history of life
What are the four eons of geologic Earth?
Hadean, Archaean, Proterozoic, Phanerozoic
What are the three subdivisions of the Phanerozoic eon?
Paleozoic, Mesozoic, Cenozoic
What are the six major milestones of the history of life?
- First single-cell organisms appear (prokaryotes)
- Photosynthesis and the oxygen revolution
- First eukaryotic cells appear
- Multicellular organisms appear
- The Cambrian Explosion
- Colonization of land
What are characteristics of the Hadean eon?
Origin of Earth, too volatile for any life
What are characteristics of the Archaean eon?
Prokaryotes arise, photosynthesis develops at end of era
What are characteristics of the Proterozoic eon?
Eukaryotes arise- first unicellular, then multicellular (including animals)
What are characteristics of the Phanerozoic eon?
Several major events regarding animal diversity
In what rocks are the earliest prokaryotes reserved as fossils?
stromatolites
The first prokaryotes to develop photosynthesis abilities are precursors to the modern day ________.
cyanobacteria
Where did oxygen accumulate towards the end of the Archaean eon?
the ocean
How can we measure the accumulation of oxygen in the ocean?
by observing bands of iron ore that are created when oxygen reacts with iron in the ocean & precipitates out
What separates the Archaean eon from the Proterozoic?
mass extinction caused by the accumulation of oxygen in the atmosphere
Why did the accumulation of oxygen in the atmosphere cause a mass extinction?
Many prokaryotes had evolved to be anaerobic to the point where O2 was toxic to them
What spurred the emergence of the ability to perform aerobic respiration?
The mass extinction caused by the accumulation of O2 in the atmosphere
When did the first eukaryotic cells appear?
~2 billion years ago, during the Proterozoic eon
How does the endosymbiont theory explain the origin of eukaryotes?
- Large prokaryote engulfed smaller prokaryote with intention to eat
- small one could do respiration so the larger one kept it
- smaller one is precursor to mitochondrion
- Later, one of these early eukaryotic cells engulfed another smaller one
- smaller one could do photosynthesis
- smaller one is precursor to chloroplast
What evidence supports the endosymbiont theory?
Mitochondria and chloroplasts are similar to existing prokaryotes
How are mitochondria and chloroplasts similar to existing prokaryotes?
- similar enzymes
- similar self-replication
- have their own circular genome
- have their own ribosomes which are more similar to those of prokaryotes
What order of events happened as a result of the evolution of photosynthesis in prokaryotes?
- O2 accumulation
- mass extinction due to O2 toxicity
- evolution of aerobic respiration
Why do all eukaryotic cells have mitochondria but not all have chloroplasts according to the endosymbiont theory?
chloroplast precursor was not engulfed by cells until much later than mitochondria precursor
When did multicellular eukaryotes arise?
~1.5 billion years ago in Proterozoic eon
What marks the transition from the Proterozoic eon to the Phanerozoic?
The Cambrian Explosion
What was the Cambrian Explosion?
massive increase in the diversity of animals and introduction of predators
When did life begin to transition from water to land?
~500 million years ago in the Phanerozoic eon
What were the benefits of transitioning from water to land?
many open niches, no predators
What were challenges of transitioning to land?
required special adaptations (i.e. lungs to breath air, changed fertilization methods)
Dramatic events that appear in the fossil record include
Mass extinctions & adaptive radiations
What is the significance of the Permian Mass Extinction?
claimed 96% of marine animal species and defines boundary between Paleozoic & Mesozoic eras
What is thought to have caused the Permian Mass Extinction?
extreme volcanoes that released enough CO2 to incr global temp and acidify oceans
What is the significance of the Cretaceous Mass Extinction?
claimed >½ marine species and eliminated land animals like the dinosaurs
What is though to have caused the Cretaceous Mass Extinction? What evidence supports this theory?
meteorite that crashed, dust blocked out sun for months; Chicxulub crater off coast of mexico
What signifies a mass extinction?
extinction is at rate much higher than the baseline rate of extinction
Mass extinctions driven by events that change…
…global conditions
Approx. how long does it take for biodiversity to recover after a mass extinction?
5-10 million years
What is adaptive radiation?
The rapid evolution of diverse species from a common ancestor
List the conditions that can lead to adaptive radiations.
- Mass extinctions
- The evolution of new, advantageous traits
- Colonization of new habitats
What 3 reasons cause adaptive radiation after a mass extinction?
- Reduced predation
- Reduced competition
- Increased niche availability
What are 2 examples of adaptive radiation due to acquisition of a new, advantageous trait?
development of placental gestation in mammals and new reproductive structures (like flowers) in angiosperms
What are angiosperms?
flowering plants
What is an example of adaptive radiation due to the colonization of a new habitat?
single ancestral plant that arrived on the Hawaiian islands 5 million years ago
What is evo-devo?
research at the interface between evolutionary biology and developmental biology
What does evo-devo demonstrate?
how slight genetic differences can produce major morphological differences
Many evolutionary changes are result of ______.
heterochrony
What is heterochrony?
evolutionary change in the rate/timing of developments events
Give one example of heterochrony.
slowed growth of leg bones led to reduction & loss of hind limbs in whales
What is paedomorphosis?
a condition where reproductive organ development accelerates more than other organs so sexually mature organisms keeps features that were only in juvenile ancestors
What do homeotic genes determine?
position of basic features Ex) position of legs
