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 Earth’s 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