Chapter 23: History of Life on Earth

Name 3 ways life on Earth can be dated. Define them.

• stratigraphy - fossils used to age sedimentary rocks, study of strata

• radiometric - radioisotopes used to determine age of rocks

• Paleomagnetic - alignment of particles in rocks, related ages of rocks to patterns in Earths magnetism ( rocks have record of magnetic field when formed)

Principles of stratigraphy

1. fossils of similar organisms found in widely separated places on Earth

2. certain fossils ALWAYS found in younger strata (layers), some in older

3. fossilized organisms in younger strata more similar to modern organisms than fossils

How are sedimentary rocks formed?

formed by accumulation of sediment

Steno

in undisturbed sedimentary rock, oldest layers (strata) are at the bottom and younger on top

Half-life

interval where half the remaining radioisotope decays

Define the Cambrian explosion

rapid increase of multicellular organisms

• marks start of Paleozoic era (542 mya)

What happened during the Cambrian explosion? (3 things)

• oxygen levels approach current level

• rapid diversification of life

• multicellular life (aquatic)

How did the Cambrian explosion end?

Mass extinction

4 ways Earths physical environment impact evolurion

• Changing land masses —> land masses break apart, species evolve on their own

  • pangea - single supercontinent

• Sea level changes —> extinction events when sea freezes

• Mass extinctions —> Massive glaciation, end-permian extinction, dino extinction

• Changes in atmosphere

Explain changes in atmosphere 2.5 bya

• Oxygen increases w cyanobacteria (used water for photosynthesis)

• oxygen accumulates —> evolution of oxidation reactions as energy to synthesize ATP

• Aerobic metabolism

aerobic metabolism

use of oxygen to make energy (ATP), faster and more efficient

Why is oxygen important?

• made complex cells possible

• 1.5 bya enough oxygen for large eukaryotic cells

• further evolution of multicellular organisms 750-570 mya

• high O₂ levels = large insects (unable to survive today)

What is biota? Name the two types.

Biota - assemblage of all kinds of organisms alive at one place/time

• fauna - animals

• flora - plants

What types of organisms are good for the fossil record?

bones, teeth, seeds, and hard-bodied (trilobites) can fossilize easier than softer structures (ex: jellyfish)

What is the background extinction rate

normal extinction rate

What is mass extinction?

extinction rate much greater than background rate

Causes of extinction

• environmental changes making growth/reproduction harder

• new species outcompeting existing species

• prey goes extinct —> predators decline

• population decreases, extinction probability increases

what is the Allee effect?

small populations have density-dependent disadvantages

Hadeon eon

• precambrian

• before life

Archean eon

• precambrian

• early life

• ends w photosynthetic organisms

Proterozoic

• precambrian

• 1st eukaryotes

Phanerozoic

• cambrian explosion (multicellular organisms, oxygen levels)

• diversification of eukaryotes

Sea levels are influenced by…..

tectonic plates

How do tectonic plates impact life on earth?

Plate movements caused the land masses to shift over time, isolating species and creating new and unique environments for organisms to evolve

What are the subdivisions of the geological time scale?

First divided into eons, then eras, then periods, then epochs