4.6 Eukaryotic Evolution U4 Flashcards
What were the main events of the Proterozoic Eon?
Great Oxygenation Event/Crisis
Supercontinents & glaciations (ice ages)
Appearance of:
Eukaryotes
Sexual reproduction
(Simple) Animals
Explain the great oxygenation event/crisis?
Cyanobacteria conducted photosynthesis-> O2 released reacted w/iron in the ocean to form rust (which can be seen in rocks- banded iron formation).-> eventually iron ran out and oxygen escaped into the atmosphere
The sudden increase in atmospheric oxygen was poisonous to many of the species that existed at this time (anaerobic species, etc), including cyanobacteria! This event caused over 90% of life on earth to die off, and luckily resulting in some species evolving to use oxygen and thrive in this new environment.
This oxygenation of the atmosphere (and removal of what was previously a LOT of methane in the atmosphere, a strong greenhouse gas) is hypothesized to have helped lead to the Snowball Earth hypothesized to have occurred after this!
What is an ice age?
Period of time during which the earth’s climate is colder than usual causing extensive ice sheets & glaciers to form.
How many ice ages have there been?
There have been multiple ice ages and within each ice age there are cycles of glaciation and interglacial periods.
What is glaciation?
w/ice sheets
What is interglacial periods?
warmer times
What is the most recent ice age?
Most recent ice age is the Quaternary Ice Age which began over 2.5 million years ago and continues today. The last glacial period (last glacial maximum) occurred over 20,000 years ago. Earth is currently in an interglacial period known as the Holocene.
What were potential causes of the cambrian explosion?
Atmospheric O2
Sea levels
continental shelf/shallow water
Calcium in ocean
Useful for forming shells
Ecological relationships
Predator & prey coevolution, etc.
Hox genes
Controls animal body plans
What was the cambrian explosion?
Rapid evolution of animal phyla & diversity
What are trilobites?
One of the most dominant species in this period!
Around ~90% of Cambrian fossils!!
Extremely diverse! (20,000+ species)
Arthropods
Scavengers, predators, filter feeders, etc!
What are Anomalocaris Canadensis?
One of the first apex predators!
Around 3 ft in size!
Name = “abnormal shrimp from Canada”
What are Hallucigenia?
Named for their
“bizarre, dream-like
quality”
May be (somewhat) closely related to tardigrades or modern-day velvet worms!
What are Opabinia?
Flexible clawed arm, with backward-facing mouth
Arthropod? Crustacean? Trilobite??
No - maybe similar to ancestral arthropod?
What are the Phanerozoic Eon Main events?
Paleozoic
Permian Mass Extinction
Mesozoic (“Age of Reptiles”)
Cretaceous Mass Extinction
Cenozoic (“Age of Mammals”)
(Later) Cenozoic
(Ongoing) Cenozoic
What are the Phanerozoic Eon Main events? Paleozoic
Cambrian Explosion!
First plants & animals on land!
Previously, all were aquatic!
Fish! Amphibians! Reptiles! Trees!
Pangea (supercontinent)
