History of Life on Earth

This lecture has links to many websites that contain supplemental information which I hope may be of interest to you. You are not responsible for the information at these sites on the exams but I hope you will take a look at some of them.

Fossils - relics or impressions of organisms from the past, preserved in rock.

    Fossils (Fig 25.1) most frequently form from:

    Paleontology - the study of fossils.

    Aging bones and rocks

1. Relative Dating
    - Law of superimposition - sedimentary rock formation (fig 22.3)
    - Index fossils
    - Eras, periods within each era, and epochs within periods. Each marked by a large extinction episode.
2. Absolute Dating - radiometric dating. (Fig. 25.2)
        - Radioactive isotope
        - Half-life
        - Carbon14/12 (Carbon 14 degrades to nitrogen 14)
        - Uranium 238 (degrades to lead 206) - only for dating volcanic rocks
        - Potassium-40 (degrades to calcium 40, then to argon 40)

Geologic History of Earth - (Table. 25.1). The Geologic Time Table

See cross-section of earth here

    - solid inner core of iron & nickel
    - molten mantle
    - solid crust - 8-65 km thick

Plate tectonics
(Fig. 25.3) (See links at end of lecture)
   - convection cells in the mantle (OH) similar to those in boiling water (OH)
   - types of boundaries (Image) (OH) and the mid-oceanic ridge (OH)
   -  Continental drift (Fig 25.4)
    - Pangaea
    - The mid-Atlantic ridge and the repeated reversal of the earth's magnetic field
   - Where'd that Indian plate go?
    - California - into the sea? The San Andreas fault - a map and a picture.
    - Wegener's evidence (
1) Africa and S. America (2) biogeograpy (3) glacial deposits
    - See drawings from 1858 by Antonio Snider-Pellegrini before and after the breakup of Pangaea, which was not even named until 1912 (by Wegener).
Alternation between hot & cold climates which resulted in:
    - the rising and falling of sea levels and the resultant changes in salinity
    - extension and retreat of ice (ice caps and glaciers)
    - caused "nuclear winters"
    - possibly caused mass extinction at end of Permian when Pangaea formed
    - some formed at areas other than boundaries. See map of earth's hot spots and creation of Hawaii
Meteorites (Fig 25.6)
    - caused "nuclear winters"
    - most important at end of Mesozoic (Cretaceous extinction - K-T boundary)
    - recently implicated in Permian extiction also
Mass extinctions (Fig 25.5)

A simple but interesting look at the origin of the earth and life from NASA.

Visit any time period at the Berkeley site. Lots of good pictures. Introduction to Evolution at Berkeley.

Geologic time table - simple one, complex one (you are not responsible for either one)

Major episodes in the history of Life (Fig 26.1) Clock analogy (Fig 26.2)

Precambrian - From the earth's creation to the beginning of the Paleozoic. also look at this site

Universe 10-20 byo
Solar system 4.5-5 byo

Earth (
OH) - 4.6 byo

- atmosphere of early earth thought to contain:
         carbon monoxide
         carbon dioxide
         water vapor
         BUT NO FREE OXYGEN, or just trace amounts (reducing environment)
- atmosphere of present day
         78% nitrogen N
         21% oxygen O
2 (oxidizing environment)
         0.035% carbon dioxide CO
          traces of rarer gases

Origin of life - life began 3.5-4.0 bya

Eukaryotes evolved about 2.1 bya and multicellular eukaryotes evolved by 1.2 bya

Image of early earth

Origin of life by chemical evolution - abiotic synthesis

- terrestrial synthesis - formation of monomers > polymers > origin of self-replication molecules > protobionts (Fig 26.12) > primitive cells
   - Miller-Urey (Fig 26.10)
    - shallow seas
hydrothermal vents             Hydrothermal vents in action
    - clay, sand, rock particles
- extraterrestrial - comets, asteroids, meteors (Panspermia)
- a lecture on origin of life by Dr. Taggart

A good article on the origin of life by Christian de Duve in the American Scientist

Define prokaryotic, eukaryotic, heterotrophic and autotrophic

The evolution of
prokaryotes Early and modern prokaryotes (Fig 26.3)

- earliest fossils are 3.5 billion years old = stromatolites - Fossil (Fig 26.4c) & Modern
- evolved 3.6 bya - 4.0 bya
- 2.0-3.5 bya
cyanobacteria (photosynthetic) oxygen revolution
- evolution of photosynthesis (Fig 27.12)

Precambrian Extinction - huge extinction event probably caused by severe glaciation.

PALEOZOIC ERA - Age of fishes 543-245 mya (Paleozoic Ocean Life - images) and a great trilobite site.

Cambrian Explosion. Timeline of the evolution of animal phyla (Fig 26.8)
    More on this here.
    - About 570-500 million years ago
    - most major animal phyla appeared during this time - Fig 32.13
Burgess shale

Ordivician - Invasion of Land - plants, animals and fungi

Devonian - first amphibians, insects

Carboniferous - those famous forests of the Carboniferous

    - Pangaea formed
   - Most recent data indicates there was probably an asteroid strike at that time also.
    - extinction of about 90% of marine and 70% terrestrial species. Possible
    - The Permian Reef Complex (Delaware Basin) of West Texas - A virtual tour of a Texas site.
          Written by K.A. Grimm

MESOZOIC ERA - Age of Reptiles 245-65 mya. Discovery of dinosaurs.

   - OH of representative animals of the Mesozoic
    - Radiation of gymnosperms, tree ferns, invertebrates & reptiles, including
map of earth at early Jurassic - about 200 mya
    - radiation of bony fishes, flying reptiles, some mammals
    - very warm, sea levels high, radiation of flowering plants, dinosaurs, small mammals
    - Extinction of Dinosaurs (
K-T boundary) (Big blank place on this page - keep scrolling!)
    - ended 65 million years ago, most think caused by asteroid impact (
OH) (Fig 25.6)
    - a great K-T Boundary site, complete with a game to play and lots of info!
    - More on the impact theory of mass extinctions.
    - A great dinosaur site!
    - Hot-Blooded or Cold-Blooded??
    - A satellite image of the Yucatan impact site of that giant asteroid.
    - An alternative theory of the extinction of the dinosaurs, gradualism, is presented here.
        by Bryan Goff, Central Connecticut State University
    - A NASA site on impact hazards of the future!
    - Levels of iridium in earth's strata.

CENOZOIC - Age of mammals 65-present

 - OH for representative extinct North and South American mammals of the Cenozoic
Ice Ages
Tertiary 65-2 mya
    - Climate cooler, sea levels lower,continents near current positions
    - Radiation of birds, mammals, flowering plants and insects.
Quartenary 2 mya - present
    - Cold clilmate, repeated glaciations, sea levels low
    - Humans evolve, many large mammals go extinct
    - The midwestern U.S., 16,000 years ago.
Human Impact
    - We've only been around a few seconds!! Geologically speaking.
Global climate change
    - Threats to biodiversity - humans causing another major extinction event?

Follow a fossil from finding to museum: http://www.dmnh.org/denverbasin2/fossil

La Brea Tar Pits: http://www.tarpits.org

Links for plate tectonics

from USGS: http://pubs.usgs.gov/publications/text//dynamic.html

from Berkeley: http://www.ucmp.berkeley.edu:80/geology/tectonics.html

from Dinosauria: http://www.dinosauria.com/dml/maps.htm