5. Learning Objectives
Students will be able to:
1. Summarize the major events of life’s history
on the geologic timescale.
2. Outline the scientific evidence for the origin
of life on Earth.
3. Describe how conditions on the early Earth
could contribute to the production of
biological molecules.
5
6. Life’s Origin Remains Mysterious
Section 15.1
Life arose on Earth about 4 billion
years ago. Scientists know little
about life’s origin or origins.
Figure 15.1
6
10. Section 15.1
The Miller experiment
simulated early Earth’s
atmosphere. Simple
molecules combined
into organic
compounds, such as
amino acids.
Figure 15.4
Life’s Origin Remains Mysterious
10
12. Figure 15.5
Certain soils can act as a template
• Clay and iron pyrite likely
catalyzed the first synthesis
reactions.
• Once a self-replicating
molecule—like RNA—
formed and replicated,
natural selection took over.
Stable molecules that could
self-replicate became more
common.
12
14. 15_page309
Membranes
• Lipid membranes
might have enclosed
some self-replicating
systems, forming the
first protocells.
• Protocells eventually
gave rise to the first
life—prokaryotes.
14
19. Section 15.1
Eventually, organisms evolved that used H2O during
photosynthesis, producing O2 as a byproduct.
Early Life Changed Earth
Figure 15.6
19
This is (obviously) a biology class. So let’s start by defining what Biology is….they have probably been giving the “Biology is the study of life” definition before….ask “Why do you think we added the word “scientific” to the definition? How does a “scientific” study differ from just a “study”?
These stromatalites are evidence of the ancient microbes that were the only form of life for 85% of the history of life on Earth before more complex life evolved. Photo from Shark Bay, in Western Australia, which is a UNESCO World Heritage Site. Image courtesy NASA.
http://www.isgtw.org/feature/cern-lends-hand-origin-life
For this unit we will begin with an explanation of the origin of Earth’s biodiversity. Then discusses how the hierarchical levels of life likely formed to produce the first living organisms. Evidence for the origins of organic molecules will be provided with an explanation of the Miller’s prebiotic experiment. Miller’s experiment showed how a chemical “soup” could form many of the molecules making up living organisms. Other models of organic evolution are also presented to support Miller’s work.
COMMON STUDENT MISCONCEPTIONS
There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in this presentation are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature.
Students believe that all evolutionary changes are gradual.
Students believe that organic evolution could not have taken place on Earth.
Students believe that the origins of life started out as random atoms coming together to form molecules.
Students believe that the early oceans were salty.
Students believe that the early atmosphere contained oxygen.
When covering the Miller experiment, it is important to stress that the conditions on the primordial Earth were significantly different from those that exist today and that one of the most important life-sustaining characteristics, free oxygen gas, is a by-product of the metabolism of primitive living organisms. Have students consider the likelihood of life continuing as it is with anthropogenic environment changes such as upper atmosphere ozone depletion and global climate change.
We will talk about prokaryotes in detail in the next unit.
