History of Life on Earth and Human Evolution

BIOL 2040 - Ch 26

Origin of Life

• big bang occurred 13.8 bya

• solar system began 4.6 bya

• 4.0-3.5 bya life emerged on earth

Fossils

preserved remains of past life on Earth (bones/shells)

paleontologists study fossils

Age and levels of rock layers

Older rock is deeper and older organisms are deeper in the rock bed

Radiometric dating

Fossils can be dated using elemental isotopes in
accompanying rock
• Radioisotopes are unstable isotopes that spontaneously decay at a constant rate

Half-life

length of time required for a radioisotope to decay to exactly one-half of its initial quantity

Four eons of earth

• Hadean

• Archaean

• Proterozoic

• Phanerozoic

Precambrian includes

• Hadean

• Archaean

• Proterozoic

Changes in living organisms are a result of

• genetic changes

• environmental changes

  • can allow new organisms to flourish

  • can also result in extinction

Extinction

complete loss of a species or species group

Mass extinctions

5 large ones

• Near end of Ordovician, Devonian, Permian, Triassic, and Cretaceous periods

• Boundaries between geologic time periods are often based on these events

• Rapid extinction of many modern species due to human activities is sometimes referred to as the sixth mass extinction

Archeaon Eon

when diverse microbial life flourished in
primordial oceans

First known fossils 3.5 billion years ago
• First cells prokaryotic
• All life forms prokaryotic during Archaeon Eon
• Hardly any free oxygen so organisms were anaerobic
• Biologists are undecided about whether heterotrophs or autotrophs came first

Stromatolites

layered structure of calcium carbonite

Origin of eukaryotes

• First eukaryotic cells arose in Proterozoic eon from within the
  domain Archaea

• Asgard archaea evolved changes to the membrane

• The most widely accepted hypothesis proposed to explain this involves a symbiotic relationship between ancient
  bacteria and archaea

Symbiotic relationship

two species live in direct contact

Endosymbiotic

one organism lives inside another (the host)

Proterozoic Eon

Multicellular eukaryotes arise 1.5 billion years ago

• individuals aggregated to form a colony

or

• a single cell divided and stayed stuck together