Mod 5/6 History of Life Flashcards
How old is earth?
4.6 Billion y.o.
Before he was a renowned evolutionary biologist, Charles Darwin accomplished in another field. What was it?
Geology
What was the estimate of the age of the earth?
70,000
What area in england did Darwin study?
The Weald
Who worked on heat and used heat modeling to estimate Earth at <20 myo? And what did he believe?
William Kelvin
Measured changes in temperature of rock and modeled using rocks in minesDid not know that the Earth was not a constant (heat flows up and down)Mine rocks were warmer than they should be due to heat flow
Did darwin agree with kelvin?
No.
What didn’t Kelvin know when forming his hypothesis about the cooling Earth?
Molten rock in the mantle and core rise and fall as their temperature changes
Atoms are
either stable or unstable•Instability was at different levels, depending on atom•Due to variation in number of neutrons
Most common isotope
Carbon 12 (6 p + 6 n)
Most rare isotope?
Carbon 14 (6 P + 8 N)
What is Half-Life equation?
𝑁=𝑁0𝑒−λ 𝑡 𝑁= number of unstable atoms N0= remaining number of unstable atoms λ= probability of decay 𝑡= time
What defines an element?
Number of protons
Radioisotopes
Some can be formed by cosmic rays •Sometimes convert nitrogen into carbon-14•Other examples•Most have been around since Earth formed•Isotopes in rocks have half-lives > 80 million years•By examining how much is left, we get an age
So earth is
4.568 billion years (4,568,000,000 years)
Radiometric dating
If you know the half-life (decay rate)
And you know how much of a radioisotope still remains
Compared to how much is stable
You can determine how much time has passed
Rubidium-87
37 protons and 50 neutrons•Half-life of 48.8 billion years
Decays into strontium-87 (Sr-87, stable)
When rocks are formed,
Contain various minerals
Each mineral contains different amounts of Rb and Sr
What do all rocks have upon formation?
All rocks have same ratio of Sr-87 to Sr-86•Regardless of ratio of Rb-87 to Sr-86
What decays to what overtime?
As Rb-87 decays to Sr-87•And as Sr-86 stays the same (it is stable)
The ratio Rb-87/Sr-86 decreases (in all rocks)
If this is plotted (as an isochron)
For all rock types
Slope of line is 𝑒𝑒λ𝑡𝑡−1
Used to determine time since formation
Rubidium -87 decays by
a neutron degrading to a proton and electron
What can this dating be used on?
Meteorites. Overall helped solve the age of the Earth.
Why did darwin think fossills were difficult to make?
Are eaten Smaller organisms consume them at microscopic level Weather erodes them Some do fossilize though Must have the right conditions Still water where silt can be deposited Mudslide that is anoxic Volcanic ash, etc.
Mineralization of organic matter can happen by?
Minerals from water fill spaces and settle
Original organic material dissolves away
Original spaces filled with other minerals
Why are fossils never safe?
Can later be exposed
Degraded by weather erosion
People come along and pick them up!
Previous organic fossils
Do not tend to have rubidium and strontium
Radiometric dating not possible
Can use nearby rock for dating
If you were to find mineralized fossils from previously organic matter, what technique could you use to date their age?
Radioisotopic dating of nearby rock strata
What can fossils tell us?
Morphology
Evolutionary relationships
Behavioral ecology
Mating, Reproduction, Feeding
What can fossils tell us?
Morphology
Evolutionary relationships
Behavioral ecology:
Mating, Reproduction, Feeding
Developmental Biology
What PHYSICAL techniques can we use to see fossil cellular structure?
SEM Scanning electron microscopes and Energy-dispersive X-ray spectroscopy of Borealopeltia
Showed: More melanin on dorsal surfaces
Indicated countershading
Seems it was preyed on by other dinosaurs
Computed tomography –allows mapping of three-dimensional characteristics of living (and fossil) organisms
What two pieces of evidence indicated that hadrosaurs used their head crests for communication?
Connected to nasal openings
Area of brain for olfaction is small
Morphology – ear bones indicated they picked up frequencies produced by resonating crests
Lagerstätten
•Deposit of well-preserved fossils
Usually due to an anoxic environment
Example: the Burgess shale (65k fossils, >93 species)•~505 to 510 mya
Biomarkers
Molecules in the fossil record that indicate the presence of life
Some larger molecules can only form through organic pathways
Some are unique to certain groups of organisms
Okenane– only made by purple sulfur bacteria
Okenane example
Found in 1.64 billion year old rocks in Australia
-indicates biological life
•Also anoxic, sulfidic ocean
•Waters would have been toxic to many organisms
Are different isotopes found in fresh and sea waters?
Yes.
Where do plants get carbon from?
Atmosphere, take up C12 better than C13
Because plants get carbon from atmospheric CO….
We Can test rock to determine if plant material is present
C3 vs C4 plants
C4 photosynthesizing plants have higher ratios of 13C/12C
Can help to determine diet in animals
Shift in human diets
What was the shift in human diets?
More C4 plants more recently
Or feeding on animals that ate C4 plants
Which of the following statements about “molecular paleontology” is true?
More recent humans appear to have shifted their diets from C3 to C4 plants (or to animals that consume C4 plants)
How long has life been on Earth?
It started as molten rock
Many pieces came together
•Formed a crust by cooling over millions of years
•Denser crust rock sank
•Lighter crust rock formed the continents
•Rocks released gases, including water vapor
•Oceans began to form
Eras
- Hadean
- Archaean
- Proterozoic
- Paleozoic
- Mesozoic
- Cenozoic
How old is life?
Potential evidence of carbon-12 enriched inclusions in a 4.1 billion year old zircon
Not conclusive
- At Darwin’s time, oldest known fossils were from Cambrian, 541 mya
- Since then, fossils have been found possibly up to 3.5 bya
What original rock can persist?
Original rock destroyed by impacts, plate tectonics
•Zircons can persist
•Sometimes have isotopes that give age
•Some show the composition from ancient Earth
Stromatolites
sedimentary rock form by layers of cyanobacteria
How does stromatolites form?
Combine with sand and other small rocks
•Build up by layers over a long time
•Rare now (because they are consumed)
•Common in Precambrian times
First single-celled life?
Stromatolites
•3.5 billion years ago
•Only life for 1.5 billion years
At Darwin’s time, oldest known fossils were from
Cambrian, 541 mya
Photosynthesis revolution?
~2.7 billion years ago
•Increase O2 in the atmosphere
Movement of Earth’s crust alter and influences what?
Climate and influences species survival
Plate movement has Changes in?
Climate •Atmosphere •Land size •Flooding •Glaciation •Volcanic activity •Meteor impact
First eukaryotes
Had membrane-bound organelles
•Endosymbiotic theory
•~1.8 billion years ago
Multicellular eukaryotes
~2.1 to 1.2 billion years ago
•Evolved from either: Aggregation
Sticky offspring
Probably colonial at first
When did animals come?
635 to 585 my
•Ediacaran fauna
Precambrian ~570 mya
Many organisms common now are “new”
Dinosaurs – 240 to 66 mya(except birds) •Mammals – 160 mya •Flowering plants – 136 mya •Grasses – 100 mya. •Early human ancestors – 7 mya• Homo sapiens – 300 kya
