Origin of Species - Lecture 3 Flashcards
What is life?
○ NASA’s definition: any system that shows Darwinian evolution
○ Involves the flow of matter, energy and information
○ Homeostasis/localised negative entropy
Where did life most likely began?
○ Deep sea 3.8-4.2 billion years ago
○ First replicating molecules may have come from proton gradients around alkaline hydrothermal vents
What is the RNA world?
Appeared around 3.8 billion years ago and then disappeared
What is the earliest life?
○ All DNA life traces back to LUCA (last universal common ancestor)
○ Probably used RNA as enzymes which could copy themselves
○ Amino acids can form spontaneously but they will have been used by life after the RNA world
○ DNA and RNA are very fragile so they need protection (a cell)
How can you have a cell without DNA?
○ Tiny pores in rocks around vents
○ Lipid “protobionts” can “reproduce” and metabolise
○ RNA can spontaneously reproduce within them
○ Glucose-phosphate can be metabolised within them
What were the first prokaryotes?
○ Methane-producing bacteria
○ O2 levels remained low
○ Cyanobacteria produce O2 which was consumed by methanogenic bacteria
○ Most methanogens died out due to changes (lack of) trace metals in the sea
What are eukaryotes?
○ Have a nucleus, mitochondria, chloroplasts (in plants), golgi bodies, sex, phagocytosis
○ 1,000,000 times the volume of a prokaryote
○ Some eukaryotes are multicellular (most lineages are unicellular)
What is eukaryogenesis?
○ Happened once around 2 billion years ago
○ Archaebacterium engulfed heterotrophic eubacterium which became mitochondria
○ Was a chance event (not a product of natural selection)
○ Energy provided by mitochondria allows for large complex life
○ 2nd event for plants: autotrophic eubacterium engulfed by eukaryotic plant ancestor
What is Ediacaran Biota?
○ Before Cambrian explosion
○ Spriggina: 3cm long worm thing with bilateral symmetry
○ Dickinsonia: Ccan reach up to 1m long and might have had a gut as it has cholesterol stuck in the fossil
○ Rangeomorphs: fractally branched, looked like plants but actually animals
○ Erniettomorphs: modular or quilted
What is the Cambrian Explosion?
○ 540-515 million years ago
○ Most of the types of animals we now see first appeared
○ Arthropods, chordates, worms, etc.
○ Soft bodies preserved in Burgress Shale (Canada), China, Greenland, Russia
Why is the Opabinia strange?
○ Five eyes
○ 7cm long
What are the potential causes of the Cambrian Explosion?
○ Physiological change - dissolved oxygen levels allow active life-style?
○ Geographical change - new sea and new niches?
○ Geochemical change - sea-level changes leads to abundance of trace metals to make exoskeletons?
○ Biological change - increase in zooplankton allows new predators to arise, increasing selection pressure?
