PoB2 Week7 C13 History of Life and Paleobiology

Earth history

Earth formed ~4,550,000,000 years ago 4550 Mya 4.55 Bya 4550 Ma 4.55 Ga The age of the earth is ~4,550,000,000 years

Radiometric Dating

Unstable isotopes of one element decay into isotopes of another element Radioactive decay occurs spontaneously with a constant probability

Rocks form with mix of three components: 1. An unstable isotope of one element 2. An isotope of the element that the first one decays into 3. A stable isotope of second element that isn't a decay product

Over time, the amount of the unstable isotope decreases and the amount of its daughter isotope increases. The amount of the third isotope stays constant.

U-Pb, Nd-Sm, K-Ar, Rb-Sr

The origins of life

Primordial Soup:

Organic molecules form readily from inorganic precursors

Nitrogen, CO2, methane, ammonia, hydrogen (lightening) => Amino acids, sugars, nitrogenous bases

Polymer synthesis on surfaces

Spontaneous formation of lipid vesicles

RNA World

Proteins, DNA

Microbial mats and Stromatolites

3500 Mya

Microbial mats: very thick biofilms

-built by phototrophic and/ or chemolithotrophic bacteria

Stromatolites: Oldest known fossils formed from many layers of bacteria and sediment.

The Oxygen Revolution

2400 Mya

the accumulation of oxygen released by cyanobacteria beginning 2.6 billion years ago

oxygen precipitates iron out of the ocean

Fossil Evidence of Eukaryotes

1800 Mya

The Cryogenian Period

geologic period (850-630 million years ago) characterized by a very cold global climate

Snowball Earth

Glacial dropstone in tropical marine sediments

The Ediacaran

time period on the geological time scale when complex life forms were developing

Abundant, globally distributed macroscopic organisms

The Ediacaran Biota: Kimberella

Maybe some evidence for familiar animal lineages

The Phanerozoic

visible life

541 Ma ago to present

The Cambrian explosion of animal diversity

Why leave more fossils:

- Hard Parts

- Predation

- Mobility

Animals diversified much earlier but left little record in the rocks: - molecular clocks - chemical biomarkers

Biostratigraphy

a relative dating technique based on the regular changes seen in evolving groups of animals as well as the presence or absence of particular species

index fossil: a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found

Pollen and Spores for land;

unicellular eukaryotes with shells diatoms, radiolarians, coccolithophores for ocean animals

Marine Faunas

Three stages: biodiversity changes mark the different stages

Invasions of land

PALEOZOIC

O2 up, CO2 down;

Cannot break down died forest

Mesozoic

Age of reptiles; flowering plants

Cenozoic Era

Age of mammals

MESSINIAN salinity crisis: The Mediterranean dried up

The great American interchange:

The biotic event triggered by the docking of North and South America in the Pliocene

The last glacial period: All of Canada was covered with ice 18,000 years ago (except for Northern Yukon). Lower sea levels at that time exposed the Bering land bridge

Radioactive decay fuels

convection cells in the earth

Three boundaries

convergent, divergent, transform

Two types of crust

continental and oceanic

continental: thick, buoyant; oceanic: think, dense

Plate movements explain biogeographic patterns

Uniformitarianism

A principle that geologic processes that occurred in the past can be explained by current geologic processes

"An attempt to explain the former changes of the Earth's surface by reference to causes now in operation"

Catastrophism

A principle that states that geologic change occurs suddenly

Georges Cuvier, 1796

Death from above, 1980

Iridium abundance (parts per billion)

Geological evidence for the end-Cretaceous impact

"Big Five" Mass Extinctions

End-Permian Mass Extinction Estimated 96% of species go extinct Coincident with formation of the Siberian Traps, a huge domain of lava that may have altered climate