The History of Life on Earth and its driving force:
How did life begin on earth?
Some actual scientific theories on the beginning of life on earth.
Early scientific theory: Spontaneous Generation
Definition: Life from non-life
Mud +Water = Ducks and Swans
Dirty Shirt + Hay = Mice
Maggots from Dead Animals
In 1658 Francisco Redi’s experiment on flies disproves spontaneous generation.
1862 Louis Pastuer’s broth and bacteria experiment also disproves spontaneous generation.
Today scientists believe life came from life: BIOGENESIS
If biogenesis is true, how did it begin?
Not spontaneous generation, but spontaneous origin.
Early earth was a harsh environment. CO 2 ,N,SO 2 ,H 2 S,NH 3 ,CH 4
Spontaneous Origin: Chemical reactions of non-living matter forming simple organic molecules.
These molecules energized by the sun and volcanic heat formed more complex molecules
These molecules became the building blocks of cells.
Miller and Urey’s experiment (1953)
Mixed water vapor, methane, ammonia and hydrogen gases in a reaction chamber, after one week’s time they found amino acids and other organic compounds.
Today scientists believe their model was slightly flawed.
Primordial Soup: Earth’s early oceans
Louis Lerman’s Bubble Model.(1986)
Gases from undersea volcanoes protected and concentrated.
Ejected into the atmosphere and exposed to lightning and uv radiation.
Fall back into the ocean as simple and complex organic compounds.
Some scientists think the molecules for life may have originated from Space.
Panspermia — the theory that microbes transmit life to habitable bodies in space; or the process of such transmission.
Starting in the 1970s, British astronomers Fred Hoyle and Chandra Wickramasinghe rekindled interest in panspermia. They found new evidence, traces of life, in the intervening dust. They also proposed that comets, which are largely made of water-ice, carry bacterial life across galaxies and protect it from radiation damage along the way. One aspect of this research program, that interstellar dust and comets contain organic compounds, has been pursued by others as well. It is now universally accepted that space contains the "ingredients" of life.
There is a big jump from organic molecules to life on earth.
Microspheres: tiny vesicles of organic molecules may have been the first step to cellular organization.
Lipid structure: Hydrophobic.
There is a lot left to be learned
Early mulitcellular life
Scientists have found the first multicellular animals that apparently live entirely without oxygen, Loricifera. The creatures reside deep in one of the harshest environments on earth: the Mediterranean Ocean's L'Atalante basin, which contains salt brine so dense that it doesn't mix with the oxygen-containing waters above. The creature's cells apparently lack mitochondria, the organelles that use oxygen to power a cell. Instead they are rich in what seem to be hydrogenosomes, organelles that can do a similar job in anaerobic (or oxygen free) environments. The find could help scientists understand what life might have looked like in the earth's early oceans, which also had very little oxygen.
Earliest Fossils found were 3.5 billion years old.
2.5 billion years ago photosynthesis evolves What impact did this cause?
Complex cells develop from Endocytosis/symbiosis (endosymbiosis)
Early life was prokaryotic, heterotrophic, and anaerobic.
1.5 billion years ago eukaryotic organisms evolve.
Fossil Record: Our Key to Life’s History
Fossils are usually found in sedimentary rock when hard parts of organisms are quickly buried in sediment.
Fossils are any evidence of past life
Examples include shells, casts, molds, bones, prints, frozen soft tissues, teeth, and others.
Paleontologists study fossil record.
They learn where to look for fossils by looking at what is going on today.
By using geologic events that take place today scientists can figure out the past.
Piece together the clues to life and the environments in which they lived.
“ The present is the key to the past.”
Geologic forces that are taking place today took place in the past.
Where do you think fossils would be best found?
Consider areas where sediments would collect and fast burial would take place.
Father of modern Geology Sir Charles Lyell (1797-1875) Explain his law of uniformitarianism to your table partner and provide an example?
Dates and ages of fossils, How do paleontologists know?
Absolute vs. Relative time measurements.
Absolute time: the actual age of a fossil or life form.
Relative time: the comparison of a fossil or object to something else such as another rock or fossil.
Tree rings can identify absolute dates based on their annual growth of tissues.
Absolute time uses radiometric dating.
Radioactive T1/2 (half life) the time it takes for 1/2 of the unstable radioactive isotopes to become stable.
Based on the known rate and the known percentages of atoms in a fossil or rack the absolute age can be determined.
Carbon Dating: T 1/2 problem.
A bone is found with 12.5% carbon 14 atoms and 87.5% nitrogen 14 (a stable atom) the T 1/2 for carbon 14 is 5,600 years. If the ratio of carbon 14 to Nitrogen 14 was 100% to 0% at the time the animal was alive how old is the fossil now?
Hint: :How much C14 will be left after 5,600 years?
Using relative and absolute dating methods, paleontologists have created a geologic time scale from the layers of sedimentary rock.
Relative Dating of rock layers and fossils/environments: Which rocks and fossils are the oldest? Why?
Geologic Time Scale
As you examine the geologic time scale note the key events, simple to complex progression of life, mass extinctions, and humans position relative to other life forms.
A change in a population of organisms over time is known as:
What is the definition of population?
Population: A group of organisms of the same species within a given area.
Six different points of evidence for evolution
#1 Fossil record
The fossil record develops from simple to complex.
Demonstrates gradual changes over time.
Combinations of fossils in the rocks allow us to reconstruct the ancient communities and thus probable ecosystems.
The gap of life in the fossil record lead people to argue for the theory of creationism.
Very little life before the Cambrian time period. (600,000,000 years ago)
Then there is an explosion of life in the fossil record.
Scientists have a different explanation for why the sudden explosion in the fossil record.
What do you think might cause the sudden appearance of many types of fossils. Hint:What are the requirements for a fossil to form? Discuss with your lab partner.
#2 Homologous Structures :
Characteristics on modern organisms that are similar because they most likely were inherited by a common ancestor
#3 Vestigial Structures
Body parts no longer used but still present from an earlier ancestor.
#4 Analogous Structures
Structures that are similar in purpose but not inherited from a common ancestor.
Environmental pressures are solved in a similar but slightly different manner.