History of Life (Jan 13-17) Flashcards
How long ago did Earth form?
4.55 billion years
What does life require?
life requires interplay between DNA, RNA, and proteins, living cells came from pre existing cells
4 Overlapping stages
1) Nucleotides and amino acids produced prior to existence of cells
2) Nucleotides and amino acids became polymerized to form DNA, RNA and proteins
3) Polymers become enclosed in membranes
4) polymers enclosed in membranes evolved cellular properties
Reducing Atmosphere
A theory that Earth’s early atmosphere was low in oxygen and rich in inorganic molecules with reducing power. This theory suggests that life on Earth could have arisen from non-living matter through a process of chemical evolution
- water vapor , N2, and CO2
- little free oxygen
- earth cooled and water vapor condensed to liquid water
Miller and Urey (1953)
showed biochemicals could be produced from simple nonbiological sources (included…)
- primitive atmospheric gases
- strong source of energy (in nature, lightning)
- yielded: HCN, CH2O, glycerine, sugars, amino acids, N-bases
Extraterrestrial Hypothesis
- organic carbon from asteroids and comets stocked prebiotic soup (meteorite studies: lots of organic carbon, amino acids, nucleic acid bases)
controversy - would they not be destroyed by intense heat during comet impact?
Deep Sea Vent Hypothesis (1988)
Key organics arouse at deep-sea vents, superheated water rich in H2S + Metal ions mixes with cold seawater
- organics formed in temperature gradients around vents
3 Hypothesis of Origin of first cell
Clay hypothesis: simple organics polymerized on solid surface into more complex organics
Cell-like structures: Protobiont - cell membrane, polymers inside contain info/ enzymatic function, self replication
Chemical Selection: RNA world - RNA in Protobionts - store info, self replication, enzymatic function
What are the advantages of DNA/RNA/Protein World
Information storage - less likely to suffer mutations
Metabolism and other cell functions - protein efficiency + can preform other task (cytoskeleton, transport)
Factors that Affect the Fossil Record
Anatomy
Size
Number
Environment
Time
Geological processes
Paleontology
Precambrian Time
includes 87% of geological time: Hadean, Archean, and Protozoic Eons
- little oxygen
no ozone, lots of UV
- first cells came into existence
Prokaryotes (3.5 billion) Eukaryotes (2 billion) and Multicellular (1.5 billion)
Ediacaran Period
- Multicellular animals appear
- mudflat animals, no internal organs or bones
- mass extinction occurred
Definition of Mass Extinction
Changes to the environment that dramatically increases the rate of extinction
Permian mass extinction
- 95% of marine species
- occurred over 500 thousands years
- caused by climate change (earth warming 6C)
Cretaceous mass extinction
- lots 76% marine species and 75% plants/animals
- likely due to asteroid impact (Chicxulub crater Mexico)
Paleozoic Era - Cambrian Period
Warm, wet, O2, no ice at poles
- marine invertebrates with shells
Paleozoic Era - Ordovician Period
warm, moist atmosphere
- diverse marine invertebrates
- primitive plants & arthropods invade first land
- end, abrupt climate change (large glaciers)
Paleozoic Era - Silurian & Devonian Period
Invasion of Land
Silurian Period:
- stable climate, glaciers melted
- lots of fish, plants, coral reefs appeared
Devonian Period:
- North dry, South wet
- Gymnosperms emerge & insects
- Amphibians emerge
- Age of the Fish
Paleozoic Era - Carboniferous Period
- rich coal deposites
- plants and animals diversified
- large plants and trees prevalent
- first flying insect
- Amniotic egg emerges (reptiles)
Paleozoic Era - Permian Period
- supercontinent Pangea
- interior regions dry, seasonal fluctuations
- first mammal like reptiles appeared
- end, largest known mass extinction
Mesozoic Era - Triassic, Jurassic, Cretaceous Period
Hot climate, dry terrestrial environment, little ice at poles
Triassic Period:
- Gymnosperm dominant
- Reptiles abundant
- 1st true mammal
Jurassic Period:
- dinosaurs became really big
- 1st bird
Cretaceous period:
- dinosaurs decline
- mammals adapted, moved into habitats vacated by dinosaurs
Cenozoic Era - Paleogene, Neogene, Quanternary Period
- Colder/drier climate
- mammals continued to adapt (birds, fish, insects diversified)
- lots of flowering plants
Primary evolution began (age of man)
Primate Evolution
Lemurs, tarsiers, monkeys, apes, humans
- descendants of tree dwellers: rotating shoulder joint, big toe and thumb, sterescopic vision (depth perception)
Also: large brain, 1 offspring, upright body
Global Superpredators
Humans, currently causing 6th mass extinction
