origin of life - new mexico state universitybiology-web.nmsu.edu/~houde/history_of_life.pdf ·...
TRANSCRIPT
Origin of Life
prebiotic – before life
autocatalysis – a reaction in which the products of the reaction
result in an increase in the rate of product formation
Age of Universe estimated 13.798±0.037 billion years
Age of solar system 4.6 billion years
Prebiotic atmosphere
- mostly methane, carbon dioxide, ammonia, hydrogen,
nitrogen and water
- virtually no free oxygen
Stanley Miller and Harold Urey‘s 1953 flask
discharge experiment
sparking (to simulate lightning) of water and simulated prebiotic
atmosphere, i.e., methane, ammonia, and either hydrogen or
nitrogen
spontaneously produces aldehydes and hydrogen cyanide
which react to form aminonitrile
which reacts with water to form the amino acid alanine
or with formaldehyde and water to form glycine
flask discharge end products (within a few days)
all of the 20 (and more) amino acids found in life forms on earth
the “building blocks of life”
this could have filled the world's oceans with amino acids in
concentrations to 10-4 M in only 10 million years – the blink of an
eye in geological time
also produced:
nucleotide purines and pyrimidines
ribose sugar
… but these do not spontaneously combine to form
deoxyribonucleotides or ribonucleotides
Why RNA was probably the first genetic material
its components (i.e., nucleotide bases and ribose sugar; not RNA itself)
are formed spontaneously in flask discharge experiments
it has both genotypic and phenotypic properties (unlike DNA or amino
acids which do only one or the other)
genotypic: it self replicates with sequence fidelity (autocatalytic); it is the
genetic material of many viruses
phenotypic: it folds to produce secondary structure with protein-like functions,
e.g., ribozymes, ribosomes, self polymerization, self splicing
it has sequence-specific affinity for amino acids, i.e., translation
transfer RNAs and ribosomal RNAs are synapomorphies of all living
organisms
ATP and GTP are used as energy sources by all living organisms
but did life begin on earth?
carbonaceous chondrite – a type of meteorite that includes
water, carbon, hydrocarbons, and amino acids (including
some that do not occur in organisms on earth)
Panspermia hypothesis – extraterrestrial origin of life
bacteria have survived extraterrestrial conditions on US space
flights
Geology - the study of earth and rocks
types of rocks
igneous – from molten magma
metamorphic – from deformed sedimentary rocks
sedimentary – the type of rock that often preserves fossils
stratigraphy – the study of sedimentary layers
superposition – the notion that younger strata rest on top of
older ones (barring deformation), introduces the concept of
relative dating
relative measures of geological time
superposition, indicator fossils, magnetic reversals
absolute measure of geological time
radioisotopic decay (probablistic)
different elements for different time intervals based on half-life
235Ur 207Pb - 0.7 billion year half-life – only good for dating inorganic rocks
40K 40Ar - 8.4 billion year half-life – only good for dating really old inorganic
rocks
14C 12N - 5730 years – only good for dating quite recently living things
Review of Plate Tectonics
Subduction zone at continental plate-ocean plate
boundary
Distilling
of lighter
silicates ‘hotspot’
island chain
Seismic Activity
vectors and rates of plate movement
fossil record of life on earth
all cellular life on earth believed to have a common origin
the evidence comes from the same genes that are shared by ALL
living things
Phanerozoic – 600 million years to present; the period of time
during which fossils of organisms with hard body parts are
preserved;
Once thought to be the complete fossil record
In fact, fossil microbes at least ~3.5 billion years old
Eons
Hadeon 4.6 to 4 billion years ago condensation of earth and moon
frequent bombardment by asteroids
turnover of early crust
Archean 4 to 2.5 billion years ago formation of most continental crust
origin and proliferation of anaerobic cyanobacteria
Proterozoic 2.5 billion to 550-500 million years ago plate tectonics in action
evidence of supercontinent (‘Rodinia’)
build-up of atmospheric free oxygen
ends with protracted Ediacaran transition to Cambrian
soft-bodied multicellular plants and animals at least by Ediacaran
Phanerozoic 550-500 million years ago to present proliferation of hard bodied multicellular organisms
stromatolites - precipitated by blue green algae
(cyanobacteria)
stromatolites - precipitated by blue green algae
(cyanobacteria)
Sectioned stromatolites
fossil cyanobacteria
~3.5 billion years old
nanotubules of possible bacterial origin between 3.77-
4.22 billion years old, just 340 million years after the
formation of the planet, Nuvvuagittuq Formation CA
Newly discovered in 2017
Xiao, Zhang,& Knoll (1998) Three-dimensional preservation of algae and animal embryos in a Neoproterozoic phosphorite. Nature. 391: 553-558.
cleavage
Precambrian
Embryos (and/or colonial
protists)
Neoproterozoic
(570 +20 MY)
Doushantuo
Formation
China
Precambrian multicellular algae Neoproterozoic (570 +20 MY)
Doushantuo Formation, China
living Porphyra algae
Dickinsonia costata Ediacaran (late pre-Cambrian 635-542MY) Australia
(soft-bodied invertebrate, lichen or colonial microbe?)
The Phanerozoic Eon
Eras Periods comments
Paleozoic 541-252 MYA Pangean supercontinent
Cambrian
Ordovician
Silurian
Devonian
Carboniferous
Permian ends with first great extinction
Mesozoic 252-66.5 MYA (“Age of Reptiles”)
Laurasia and Gondwana supercontinents
separated by equatorial Tethys Sea
Triassic
Jurassic
Cretaceous ends with second great extinction
Cenozoic 66.5 MYA-present (“Age of Mammals”)
modern continents
Paleogene
Neogene
Era Periods comments
Paleozoic 541-252 MYA Pangean supercontinent
Cambrian first animals with hard body parts
Ordovician most invertebrate Phyla present
brachiopods and cephalopods dominant
all animals marine
first land plants
first cephalochordates and agnathans
Silurian extensive continental seaways
jawless fish flourish
first jawed fishes
land arthropods
Devonian all fish present
first amphibians
first winged insects
Carboniferous tropical/subtropical, wet
lobe finned fishes dominant
first reptiles
Permian breakup of Pangea
continental elevation
cooler
ends with first great extinction
Era Periods comments
Mesozoic 252-66.5 MYA (“Age of Reptiles”)
Laurasia and Gondwana supercontinents
separated by equatorial Tethys sea
hotter and arid
Triassic Gymnosperms dominant
first mammal-like reptiles
first dinosaurs
Jurassic formation of Atlantic Ocean begins
development of continental seaways
first birds
Cretaceous Angiosperms
ends with second great extinction
Chicxulub Crater from http://www.atlasobscura.com/places/chicxulub-crater
Chicxulub Meteor impact-generated wildfires Daniel D. Durda, NASA/UA Space Imagery Center's Impact Cratering Series http://www.lpi.usra.edu/science/kring/epo_web/impact_cratering/enviropages/wildfires.html
Era Periods Epochs comments
Cenozoic 66.5 MYA - present (“Age of Mammals”)
Paleogene Paleocene Archaic mammals
Eocene modern mammals and birds
first anthropoids
Oligocene Antarctic circumpolar current
latitudinal thermal stratification
global cooling
first apes
Miocene
Pliocene first hominids
Neogene Pleistocene first humans
Holocene
sessile crinoid (above)
Ordovician Echinoderms
free-swimming cystoids
Ostracoderms: the earliest jawless fishes Ordovician-Silurian
Devonian Ostracoderms
from Wyoming
Ostracoderm
head armor
Ostracoderm
nervous system
pharynx
Placoderms: earliest jawed fishes Silurian-Devonian
Placoderm
head armor
Paired appendages
Bothriolepis Devonian Wyoming
Dunkleosteus (arthrodire placoderm) Devonian apex predator
Dipnoi: lungfishes
Crossopterygii: coelocanths
Sarcopterygii: fleshy finned fishes
Devonian-Carboniferous