Evolution FROM DARWIN TO THE PRESENT Part IV: A short history of life on earth
Ages of the Earth: a geological time scale
Who are the players? Currently we recognize six distinct kingdoms in two main divisions: Procaryotes: lack a nucleus and membrane-bound organelles Eubacteria: (Monera) mostly single celled organisms with a cell wall. If colonial, no specialization. Archebacteria: ( extremophiles ) single celled organisms with a cell wall, but differ from eubacteria in the chemical makeup of the cell membrane and wall and DNA structure. Eukaryotes: nucleus and membrane-bound organelles present Protista: Single celled or colonial organisms with a nucleus and membrane-bound organelles. Fungi: single- and multicellular heterotrophic organisms with a cell wall containing chitin and membrane-bound organelles. Plants: autotrophic multicellular organisms with a cell wall and membrane-bound organelles including chlorophyll. Animals: multicellular organisms without cell walls, but with membrane-bound organelles.
Tree of Life 6 kingdoms: Eubacteria (monera) Archaebacteria Protista Plantae Fungi Eukaryota
A Molecular Phylogeny of Animalia
Archaebacteria First classified by Carle Woese in 1977 Generally accepted by biologists in mid 1980s Eubacteria Archaebacteria Eukaryota Nucleus No No Yes Circular DNA Yes Yes No Histones on DNA No Yes Yes Membrane-bound organelles No No Yes Unicellular Mostly All Only protists Cell membrane Glycerol lipids Glycerol isoprenes Glycerol lipids Cell wall Peptidoglycan No peptidoglycan Cellulose or chitin Transcription Simple RNA polymerase. begins with fmet Several complex RNA polymerases. Begins with MET As for Archeabacteria
Phylogeny of Animalia ((Molluscs,Annelids Platyhelminths, and other taxa) (Chordates, Echinoderms, Hemichordates) Published by AAAS A H Knoll, S B Carroll Science 1999;284:2129-2137
The earliest known signs of life (microfossils, organic signatures [e.g., isotope ratios]) date back to about 3.5 billion years ago, around one billion years after the formation of the earth. Thus life must have begun before that. How long before that, we don t know. But How did it start??
Where did it all start? Here s Darwin s take: It is often said that all the conditions for the first production of a living organism are now present, which could ever have been present. But if (& oh what a big if) we could conceive in some warm little pond with all sorts of ammonia & phosphoric salts, light, heat, electricity &c present, that a protein compound was chemically formed, ready to undergo still more complex changes, at the present day such matter wd be instantly devoured, or absorbed, which would not have been the case before living creatures were formed. Letter to J. D. Hooker 1 February 1871
But Darwin was wrong. Conditions on the early earth were not remotely the same as today!
Miller and Urey (1953):
The earliest form of life originated in a volcanic hydrothermal flow at high pressure and high temperature. It had a composite structure of a mineral base with catalytic centers (predominantly iron and nickel, but also perhaps cobalt, manganese, tungsten and zinc). The catalytic centers catalyzed carbon fixation pathways generating small molecule organic compounds from inorganic gases (e.g. carbon monoxide, carbon dioxide, hydrogen cyanide and hydrogen sulfide). New metabolic products further accelerated the catalysts. The idea is that once such a primitive autocatalytic metabolism was established, its intrinsically synthetic chemistry began to produce ever more complex organic compounds, ever more complex pathways and ever more complex catalytic centers.* *(after Wikkipedia)
RNA World Hypothesis
Earliest life: blue-green algae
Other factors affecting evolution of life on earth: Continental Drift
The Snowball Earth hypothesis proposes that Earth's surface became entirely or nearly entirely frozen at least once, sometime earlier than 650 Mya (million years ago). A number of unanswered questions remain, including whether the Earth was a full snowball, or a "slushball" with a thin equatorial band of open (or seasonally open) water.
Life on the Earth
Earliest signs of life Warrawoona Group (North Pole, Australia): sedimentary rocks dated to 3,471±5 million years ago.
Lynn Margulis Enter the Eukaryotes
Some Early Fossils: Doushantuo Rocks, 600mya A H Knoll, S B Carroll Science 1999;284:2129-2137 Published by AAAS
Ediacaran life: 550 MYA: Precursors to Cambrian explosion or aberrations?
Cambrian Explosion For 2.5 billion years all life was unicellular prokaryotes (eubacteria and archaebacteria). About 2.7 billion years ago eucaryotes arose Around 1 billion years ago multicellular forms arose Suddenly, 500 million years ago within 70 to 100 million years, a blink of an eye in terms of the 4.5 billion year life of the earth, ALL the present phyla had arisen and some bizarre forms were lost, never to be seen again.
Cambrian Burgess Shale Organisms: False start?? ca 505 Million Years Ago
The Ordovician Sea, 488 million years ago The Ordovician Period lasted almost 45 million years. During this period, the area north of the tropics was almost entirely ocean, and most of the world's land was collected into the southern supercontinent Gondwana.* *AMNH exhibit text
The Permian Sea, 270 Million years ago The world at the time was dominated by two continents known as Pangaea and Siberia, surrounded by a global ocean called Panthalassa. The Carboniferous rainforest collapse left behind vast regions of desert within the continental interior. Amniotes, who could better cope with these drier conditions, rose to dominance in place of their amphibian ancestors. The Permian (along with the Paleozoic) ended with the Permian Triassic extinction event, the largest mass extinction in Earth's history, in which nearly 90% of marine species and 70% of terrestrial species died out.*
The Cretaceous Sea, 145 million years ago The Cretaceous was a period with a relatively warm climate, resulting in high sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct marine reptiles, ammonites and rudists, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds, as well as flowering plants, appeared. The Cretaceous ended with a large mass extinction, the Cretaceous Paleogene extinction event, in which many groups, including non-avian dinosaurs, pterosaurs and large marine reptiles died out.*
Today
This Photo by We end with a little perspective: in the history of the earth (4 billion years) we modern humans been around for perhaps 0.005% of the time (200 thousand years). Dinosaurs were around for 4.1% of the time (165 million years), about 820 times as long. A history of life in 24 hours