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