Evolution

1
Evolution

• The History of Life on Earth

2
The Record of Life

• Early History of Earth
• Early Earth was inhospitable
• It was probably VERY hot
• The atmosphere probably contained very little
  free oxygen, but lots of water vapor and other
  gases, such as carbon dioxide
• By about 3.9 billion years ago, Earth may have
  cooled enough for the water to condense.

3

• History in rocks
• The oldest rocks that have been found on Earth
  are about 3.9 billion years old.
• Fossils clues to the past
• Fossils are physical evidence of organisms that
  lived long ago.
• They may be preserved in amber, rock, or ice.
• They are used to learn about ancient species.
• It is thought that about 99 of species are
  extinct.

4
Fossils
5

• Paleontologists are detectives to the past.
• They study fossils to determine the kinds of
  organisms that lived in the past and to sometimes
  learn about their behavior.
• They also study fossils to gain knowledge about
  ancient climate and geography.
• Most fossils are found in sedimentary rock.
  Layers of these rocks form by processes that
  prevent damage to the organism.

6
Sedimentary Rock
7
Determining the age of fossils

• Relative Dating
• If rock has not been disturbed, the layers closer
  to the top are newer than the deeper layers.
• Radiometric (Radioactive) Dating
• Radioactive isotopes are atoms with unstable
  nuclei that break down, or decay over time,
  giving off radiation. (See handout)
• Potassium-40 is used for very old fossils.
  (Half-life is 1.3 billion years)
• Carbon-14 is used for fossils less than 50,000
  years old. (Half-life is 5730 years.)

8
Determining the age of fossils

• These methods can produce inconsistent results so
  multiple samples are run as well as many
  different methods to obtain the rocks age.

9
Geologic Time Scale

• Based on evidence from Earths rocks.
• Divided into 4 eras
• Precambrian
• Paleozoic
• Mesozoic
• Cenozoic
• Division are distinguished by the organisms that
  lived during the time period.

10

• The fossil record indicates that there were
  several occurrences of mass extinction that fall
  between time divisions.
• A mass extinction is an event that occurs when
  entire groups of organisms disappear from the
  fossil record almost at once.
• After Precambrian Time, the basic divisions of
  the time scale are eras and periods.

11
Geologic Time Scale
12
A trip through geologic time

• Precambrian - Covers about 88 of Earths
  history. At the beginning only unicellular
  prokaryotes were around. Then 1.8 billion years
  ago, eukaryotic organisms appeared. Before the
  end of this era, sponges and jellyfish filled the
  oceans.
• Paleozoic many vertebrates and invertebrates
  lived during this era. Some call this an
  explosion of life because of the increase in
  diversity of life forms. Amphibians and reptiles
  appeared during this time.

13
A trip continued

• Mesozoic many call this the Age of the
  Dinosaurs, yet many other organisms lived during
  this time. Mammals began to evolve during this
  time.
• Archaeopteryx lived during this time. It was a
  dinosaur with feathers.

14

• It is thought that early in the era the
  continents were merged into 1 large land mass
  that later broke up and drifted apart.
• Cenozoic (era that we now live in) sometimes
  called the Age of Mammals because mammals became
  common during this time.

15
The Origin of Life

• Origins Early Ideas
• Spontaneous generation - nonliving material can
  produce life.
• This hypothesis was tested by Redi using decaying
  meat.
• This was also known as abiogenesis (life from
  nonliving)

16
Redis Experiment

• 
  
  

17
The Origins of Life

• Pasteurs Work proved the theory of biogenesis
  (life from other living organisms)
• Biologists have accepted the concept of
  biogenesis for more than 100 years, but this DOES
  NOT answer the question how did life begin on
  Earth?

18
See handout on How did Life Begin

• Divine Origins
• Meteorites
• Primordial Soup
• Bubbles
• AN RNA world
• Read about these and summarize them in your notes!

19
Endosymbiont Theory

• Proposed by Lynn Margulis in the early 1960s
• Explains how eukaryotic cells may have arisen.
• Simply stated, the theory of endosymbiosis is the
  concept that mitochondria and chloroplasts are
  the result of years of evolution initiated by the
  endocytosis of bacteria and blue-green algae
  which, instead of becoming digested, became
  symbiotic.  

20
(No Transcript)
21
Endosymbiont Theory contd

• New evidence has been found to SUPPORT this
  theory.
• Chloroplasts and mitochondria have their own
  ribosomes that are similar to those in
  prokaryotes.
• Chloroplasts and mitochondria also reproduce
  independently of the cells that contain them.