Sands of Time: First Cells and the Tree of Life Charley
Kirlinkus Terms universal tree of life Bacteria Archaea Eucarya
root of tree of life lateral (horizontal gene transfer Apex chert
Cyanobacteria banded-iron formations stromatolites universal tree
of life Bacteria Archaea Eucarya root of tree of life lateral
(horizontal gene transfer Apex chert Cyanobacteria banded-iron
formations stromatolites 4 billion yrs. 3.5 billion Apex Chert
Fossils of Western Australia 3.5 billion yrs. Living 1.5 billion
Living 850 Ma 950 Ma J. W. Schopf Cradle of Life (1999) 2.1 billion
Cyanobacteria Photosynthetic O 2 -producing Utilize CO2+H20 Oldest
known sedimentary rocks Banded iron formation, Isua, Greenland
billion years old Carbonaceous graphite particles From banded iron
of Greenland 3.7 billion years old ratio 12 C to 13 C in graphite
particles suggest they might be produced from living cells Presence
of free O 2 In iron-oxide-rich bands Banded-Iron Formations
(between 3.5 billion - 2 billion yrs J. W. Schopf Cradle of Life
(1999) Besides fossils, which are extremely spotty in the fossil
record, what other approach can we use to infer the earliest living
cells? 18S rRNA Woese (1996) J. W. Schopf Cradle of Life (1999)
Using Gene Families to Root the Tree Lateral Transfer of Genes How
Cellular Life Began 1. Chemical systems existed before they became
packaged Into cells-- primordial naked genes able to
self-reproduce. 2. Their chemical makeup caused these living
molecules to cluster together into globules, like ancestors of
walled cells. 3.First cells were powered by a simple form of
metabolism that laid the foundation for later complicated
metabolism. J. W. Schopf Cradle of Life (1999) Probably looked much
like a bacterium Did the common ancestor use DNA to store
information? Eucarya are vastly different Parsimony EARLY WORLD 3.5
billion yrs ago -- Apex Chert, Australia J. W. Schopf Cradle of
Life (1999) Eukaryotic Algae 2 billion yrs Single-cell Eucarya
fossils Earliest ~ 2 billion yrs. Origin of organelles:
mitochondria and chloroplasts Origin of organelles: mitochondria
and chloroplasts Proteobacteria Cyanoobacteria Horizontal Transfer
J. W. Schopf Cradle of Life (1999) 1. What was Earths environment
like when life arose? 2. How is life defined, and how did it arise
from non-life? 3. What were the characteristics of the very first
cells? HARD QUESTIONS
