“Scientific facts” don’t always give us clear answers to important questions.
Who decides what to do with “scientific facts”?
What is “life” or “living”Something that utilizes energy ?
3Fe + 4H2O <-===-> Fe3O4 + 4H2Iron water iron (II,III) oxide hydrogen
What is “life” or “living”
Maintains status quo (homeostasis)?
Farmer fixing his fence (life)vs
Buffered lake (non-living)
Definition of life:
“I can not define it, but I’ll know it when I see it” -Supreme Court Justice Stewart
Life on Mars?Life in extreme Earth environments
Bacillus living at 55°C (131°F)
A novel thermophile isolated from
>300°C, 1500m deep, geothermal
water pool
Definition of life:
“I can not define it, but I’ll know it when I see it” -Supreme Court Justice Stewart
Maybe not so easy after all!
Symptoms of life:
Order, reproduction, growth, development, energy utilization, response to environment
But what distinguishes “life” from non-living chemical reactions?
The physical properties of living things can change, and these changes can be
inherited by offspring
The physical properties of living things can change, and these changes can be
inherited by offspring
This is possible because the physical properties of “life” are determined by a program.
This program can be copied, and when it is copied, it can be changed (mutated)
The physical properties of living things can change, and these changes can be
inherited by offspring
This is possible because the physical properties of “life” are determined by a program.
This program can be copied, and when it is copied, it can be changed (mutated)
Life is unique because it is a set of chemical reactions that can EVOLVE
So, we know what makes “life” unique
But there are still many questions about how all the diversity of life came to be…
Life is different from “non-living” things because life can Evolve
Evolution inevitably results in Natural Selection and Descent with Modification.
What’s that, and what’s the result?
Natural selection
1. The members of a population have heritable variations.
2. The population produces more offspring than the resources of an environment can support.
3. There is competition for resources; as a result, the better adapted individuals survive and reproduce more than the poorly adapted.
4. Across generations, a larger proportion of the population becomes adapted to the environment.
Natural Selection leads to Descent with Modification
Once you have life, and competition for resources, natural selection will lead a population to change over time.
Birds. Fig 1.11, page 9Dogs (artificial selection)
Descent with modification can lead to new species
How much of life’s diversity can be explained by
descent with modification?How many different times was life created from non-life in order to get all this diversity?
All modern life on Earth is related by descent from a common ancestor
(evolution). Why do we believe this?
Because all life is descendent from one original life-form through an evolutionary process, we can work backward through time to modern life’s earlier and more simple form.
Same 4 nucleotides in DNA
Same central dogma
Same 20 amino acids in protein
All life descended from one common ancestor
Figure 1.4, page 6.
Three main branches (Domains)
When did this occur? And how do they know that?
How old is the oldest fossil?
Tape measure:
25 feet = 2.5 billion years
1 foot = 0.1 billion = 100 million years
1 inch ~ 10 million years
1/8 of inch ~ 1 million years
width of hair (~1/1000 inch) = 10,000 years
When did all this happen?
4 3 2 1 todayTime - billions of years ago
Earth forms
Period of heavy bombardment
Carbon isotope (first evidence of life)
First fossil microbes
Oldest eukaryotic fossil
dinosaurs
hominids
Animal diversity begins
Oxygen accumulates in atmosphere
And what does it mean?
When did all this happen? Geological timeline
Billion years ago What was happening 15 universe formed in Big Bang 4.5 Earth formed 4.0 Heavy bombardment stops 3.85 Fossils evidence of life (?) 2.0 Fossils of eukaryotes (?)
0.5 multi-cellular life becomes abundant 0.05 dinosaurs go extinct 0.005 chimp/human diverge 0.0001 firs modern humans 0.00001 humans colonize Americas (Indians) 0.000005 ancient Egypt, Greece, Rome, etc 0.0000005 dark ages of Europe 0.00000005 your parents were born
Life started quickly (~200 my), but intelligent life came so late it might have missed the party all-together (human intelligence arrived after 4 by of evolution, with only another 1 or 2 by left before all life on Earth ends)
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