The origins of life - Deep time

Eon

Lagest unit of geologic time. It is made up of two or more eras.

Eras

Second longest unit of geologic time. They are further divided into periods.

Hadean eon

First 500 to 700 million years of earths history. No rocks exist and Earth was pummelled with asteroids from this eon.

Archean eon

Life emerged during this eon ( 3.5 billion years ago ) Occurring around the same time the eaths surface cooled.

Proterozoic ( “ early life “ ) eon

Two billion years into earths history ( beginning 2.5 billion years ago ). Characterized by formation of rodinia.

Phanerozic eon

Cambrian period showed diversification of multicellular organisms. Birds and mammals have existed for 4% of earths existence. Human present for 0.2% of earths history.

Earths early atmosphere likely consisted of

• Carbon dioxide ( CO2 )

• Nitrogen gas ( N2 )

• Water vapor ( H2O )

• Hydrogen gas ( H2 )

• Other sulfur, nitrogen, and carbon compounds.

Reproducing earths early atmosphere - The miller very experiment

In 1953, Miller and Urey reproduced early atmosphere conditions. Assembled reducing atmosphere rich in hydrogen and no oxygen gas. Atmosphere places over liquid water and simulate lightning with sparks.

Single-celled organism were the first life-form

liquid bubbles could increase the probability of metabolic reactions, which could lead to cell membranes. RNA may have been first genetic material.

Landmarks in the evolution of metabolism

• Oxygenic photosynthesis

• Carbon fixation

• Nitrogen fixation

Oxygenic photosynthesis

Produced atmospheric O2 and reduced the amount atmospheric CO2

The three monophyletic domains

• Eubacteria

• Archaea

• Eukaryotes

Eubacteria and Archaea

Bacteria and archaea ruled the earth for 1 billion years. They are distinct from eukaryotes in that they have much less compartmentalization - singled celled organisms.

Eukaryotes

Compartmentalization of cells enabled the advent of eukaryotes. They developed an extensive endomembrane system, that is responsible for structures such as the nuclear membrane ( not found in bacteria and archaea ), which accounts for increased complexity in eukaryotes.

Compartmentalization

The physical separation of bio-logical reactions into distinct spaces. Eg. Membrane-bound organelle, like mitochondria and the endoplasmic reticulum ( ER ), subdivide the cytoplasm into compartments.

Endosymbiosis

Two organisms living together with one inside the other. Eg. Mitochondria are the descendants of the parasite rickettsia and chloroplasts derived from cyanobacteria.