HISTORY OF LIFE

1
HISTORY OF LIFE

• Chapter 14

2

• How old is the Earth?
• What changes have occurred?
• What is a Mass Extinction?
• How do we know they happened?

3
Field Museum Trip

• Important Questions
• 2,4,9,16,21,24,27,32,43,52,59

4
The Record of Life

• Ch. 14, Sec 1

5
Early History of Earth

• 5 billion years ago our solar system was formed
  as a swirling mass of gas and dust
• Gravity pulled this material together to form the
  sun
• Remaining gas and debris circled the newly formed
  sun
• Collisions between the space debris created the
  planets

6

• Earth formed about 4.6 billion years ago, dated
  by studying the layers of rock that make up the
  planet
• Young Earth was hot, there was no atmosphere to
  block UV rays from the sun
• No oxygen to breath
• A lot of carbon dioxide and water

7

• Life originated in Earths oceans 3.9-3.4 billion
  years ago
• Early life forms would have been very similar to
  bacteria

8
History in Rocks

• Rocks provide information about Earths history
  including the history of life on Earth
• Paleontologists study ancient life and fossils

9

• Fossils are found in sedimentary rock
• Organism gets buried in mud, sand, or clay after
  they die
• More sediment gets layered over the organism,
  over time the minerals in the sediment replace
  the minerals in the skeleton

10
(No Transcript)
11
Dating Fossils

• Relative Dating (stratigraphy) layers of rocks
  have different ages, the youngest layers on
  top older fossils found in older layers of rock
• Radiometric Dating atoms in the fossil break
  down at a certain rate, age of the fossil depends
  on the ratio of atoms to broken down atoms

12
Geologic Timescale

• Begins with the formation of Earth and goes
  through present time
• Scale is divided up by the kinds of organisms
  that lived during that time

13

• Layers of rock match up with the Geological
  Timescale

14
Organization of the GTS

• Broken down into 4 Eras, each era is further
  broken down into Periods
• The eras and periods are characterized by
  specific events and specific organisms
• Mass Extinction many organisms disappear from
  the GTS almost all at once

15
4 Eras

• 1. Precambrian Era
• Beginning of the GTS, longest era 87 of Earths
  history
• Oldest rocks are from the Precambrian, oldest
  fossils too
• First organisms were single celled

16

• 2. Paleozoic Era
• Cambrian Explosion occurred during the Cambrian
  Period
• Enormous increased in diversity of life in oceans
• Organisms with backbones emerged
• Mass extinction occurred at the end of the
  Paleozoic Era killing off 90 marine life, 70
  land life

17

• 3. Mesozoic Era
• began 248 million years ago
• Dinosaurs died out during another mass extinction
  making room for mammals
• Meteor crash could have caused the mass extinction

18

• 4. Cenozoic Era
• Began 65 million years ago
• Increased diversity in mammalian life
• Modern humans appeared 200,000 years ago

19

• As you move towards the bottom of the rock
  layers, you move back on the Geological Timescale
• Similar fossils found on different continents
  because at several times in Earths history the
  continents were connected

20
(No Transcript)
21

• Pangea existed 250 million years ago
• Plate Tectonics the surface of Earth is made up
  of plates that drift on top of a molten layer of
  rock
• http//www.nature.nps.gov/geology/usgsnps/animate/
  PLATES_3.MPG
• http//www.ucmp.berkeley.edu/geology/tecall1_4.mov

22
(No Transcript)
23
The Origin of Life

• Ch. 14, Sec. 2

24
(No Transcript)
25
Spontaneous Generation

• Pre-17th century it was believed that living
  things arose from nonliving things through a
  process called Spontaneous Generation

26

• 6th century BC Greek philosophers propose life
  arose when sunlight was shined onto mud
• Why?

27

• 1600s It was believed that mice appeared from
  rotten grain
• Why?

28
Francesco Redi (1626-1697)

• Mid-17th century people believed flies were
  spontaneously generated from rotting meat
• Redi was a scientist who noticed a life stage to
  the flies on the rotten meat
• 1. Maggots
• 2. Pupa
• 3. Flies
• He observed that the maggots appeared where flies
  had landed first

29
(No Transcript)
30

• Redi predicted that if the meat could be kept
  away from the flies, then there would be no
  maggots on the meat
• He did not believe that flies spontaneously
  generated from meat!!!
• So he set up his experiment

31

• Control Group uncovered jar of meat, flies
  layed eggs, which hatched into maggots, which
  turned into more flies
• Experimental Group covered jars of meat, flies
  have no chance to lay eggs, new flies do not
  appear

32
Louis Pasteur (1822-1895)

• Finally disproved spontaneous generation once and
  for all! 200 years after Redis experiment
• Pasteur set up an experiment where boiled broth
  was exposed to air, but microorganisms couldnt
  fall in

33

• By the 1800s scientists understood (thanks to
  the microscope invented a century ago) that
  microorganisms (bacteria viruses) caused people
  to get sick
• But.

34

• Some scientists still believed that bacteria and
  viruses spontaneously generated from the air
• Pasteur proved them wrong with his experiment

35

• Boiled broth was exposed to air in a specially
  shaped flask over a period of time but nothing
  grew
• Once the neck was broken off bacteria grew in the
  broth
• Bacteria did not spontaneously grow from the
  air!!!

36

• Thanks to Pasteur.
• Biogenesis living organisms come from other
  living organisms

37
Modern Experiments on Origins

• All elements found in organic compounds needed to
  form biomolecules existed on Earth since its
  formation
• Early atmosphere contained Ammonia (NH3),
  Hydrogen Gas (H2), Water Vapor (H2O), Methane
  (CH4)

38

• Under high temperature the gases might have
  formed simple organic compounds (contains Carbon)
  like amino acids
• When Earth began to cool the organic compounds
  would have condensed with the water vapor and
  collected in lakes and seas

39
Stanley Miller Harold Urey (1953)

• Recreated the conditions of early Earth in the
  lab on a smaller scale
• Included chemicals present at the time and an
  energy source similar to what as present at the
  time
• Able to generate amino acids (biomolecule)

40
(No Transcript)
41
Alternative Hypotheses

• 1. Life (biomolecules) emerged in ice (Stanley
  Miller)
• Within ice there are chemicals to create
  biomolecules microscopic pockets of water

42

• Water freezes forcing the chemicals to be close
  together which increases the chances of chemical
  reactions occurring
• When the ice melts the biomolecules generated are
  released into oceans

43

• 2. Life (biomolecules) emerged in deep sea vents
• Vents provide the heat chemicals that could
  cause chemical reactions to generate biomolecules

44
Formation of Protocells

• Protocell Heating the amino acids can cause
  them to take on some life activities like growth
  and division

45
First True Cells

• No direct evidence of the first cells, scientist
  can only analyze data that we collect now
• Early Earth had little oxygen, oldest fossils
  thought to be cells resemble the size shape of
  some living prokaryotes, the first cells had
  organic molecules to eat

46

• Therefore.
• The first cells were anaerobic, heterotrophic
  prokaryotes
• Anaerobic respiration that doesnt require
  oxygen
• Heterotrophic needs to eat other things in
  order to get the organic molecules needed for
  life

47

• Next evolved
• Autotrophs make their own food
• Early autotrophs similar to present day
  Archaebacteria
• Archaea prokaryote organisms that thrive under
  harsh conditions, make food through
  chemosynthesis
• Chemosynthesis CO2 is the carbon source, energy
  comes from the use of inorganic chemicals

48
(No Transcript)
49

• Next evolved
• Photosynthetic prokaryotes
• Autotrophs now able to use sunlight energy to
  make food
• Created oxygen for the atmosphere which allowed
  for an increase in diversity of life because now
  there was an ozone layer (provides protection
  from UV light)

50
Endosymbiotic Theory

• Eukaryotic cells evolved from Prokaryotic cells
• Symbiosis close, long term relationship between
  species
• An ancient prokaryote engulfed another prokaryote
  and instead of digesting it they lived together

51

• This explains why mitochondria has its own DNA