Several methods can be used to date events in Earth's history.
The relative age of rocks and fossils is revealed by studying undisturbed rock layers.
The age of rocks can be measured using the decay of radioactive isotopes and half-life.
Sometimes there isn't enough rock or fossils to measure, so scientists use other techniques.
Earth's magnetic poles can change and sometimes even reverse.
Rock layers record these changes.
Other methods of dating Earth include changes in sea levels and continental drift.
Scientists have learned that Earth has changed since it formed 4.5 billion years ago.
The continents have changed.
The climate has gone through periods of cooling.
The oceans have been raised and lowered many times.
Volcanic activity has changed Earth and killed off many species.
The dinosaurs went extinct because of meteorites bombarding Earth from outer space.
There have been five major extinctions.
The atmosphere was devoid of free oxygen 4 billion years ago.
Free oxygen was provided for the oceans and atmosphere by organisms called stromatolites.
The oxygen level killed off most of the prokaryotes.
The high oxygen levels made it possible for life to be diversified on land and in the seas.
The sudden appearance of many present-day animal species was the result of the Cambrian explosion.
Evidence for evolution can be found in many areas of scientific study.
The fossil record shows the existence of extinct or evolving species.
The age of fossils can be measured with radiometric dating and half-life.
The oldest fossils are from the first organisms to develop on Earth.
There are many transitional forms that link older fossils to modern species.
A fossil that links birds and reptiles is called Archaeopteryx.
The fossil record shows that the organisms that are alive today are a tiny fraction of the organisms that lived in the past.
Most life on Earth went extinct.
The idea that evolution has occurred in all species is supported by scientific evidence.
The study of different structures contributes to the understanding of evolution.
The internal bone structure of the bat, whale, and human arm are the same.
The structures have a common origin and reflect a common ancestry.
The same function can be found in bat's wing and fly's wing.
The similarity is superficial and reflects an adaptation to similar environments, not a descent from a recent common ancestor.
The appendix is evidence that structures have evolved.
When human ancestors ate a very different diet, the appendix was needed.
Common biochemical pathways can be found in organs that have a common ancestor.
The more closely related organisms are, the more similar they are.
Humans and mice are mammals.
Medical researchers are able to test new medicines on mice because of this close relationship.
There are several electron carriers in the electron transport chain.
All aerobic organisms have it.
It is used to determine ancestral relationships and build cladograms.
Humans and Chimpanzees have the same sequence of cytochrome c.
Closely related organisms go through the same stages in their development.
The gill pouches on the sides of the embryos' throats is a stage in which they go.
The gill pouch develops into the gills in fish.
They become eustachian tubes in the ears in mammals.
The cells that carry out aerobic cell respiration are all contained in aerobic organisms.
Some organisms are more closely related to each other than others.
The cytochrome c in human cells is similar to that of our closest relatives, the Chimpanzees and the gorilla, but different from that of a pig.
The theory of plate tectonics states that the continents and oceans rest on giant plates that float on top of the hot mantle.
The continental drift is caused by the slow, continuous movement of the plates.
The North American plate pulls away from the Eurasian plate at a rate of 2 cm per year.
Plates collide as Continental drift causes mountains to form.
The Himalayan Mountains were formed about 45 million years ago when the Indian plate collided with the Eurasian plate.
Plates have changed the flora and fauna of Earth over millions of years.
Pangaea was formed about 250 million years ago because of plate movement.
Sea level was lowered and shallow waters were drained.
There were a lot of species that went extinct.
The distribution of life on Earth has changed due to Continental drift.
One example is the fact that the true mammals, the eutherians, are found only in Australia.
Fossil evidence shows that marsupials came to Australia via South America and Antarctica, even though the continents were still joined.
Australia was set afloat like a giant raft when the continents broke apart.
The true placental mammals, which were not adapted to the Australian environment and climate, went extinct, while the marsupials filled every available niche.
The true mammals survived and diversified, while the marsupials went extinct.
The ancient world was influenced by the theories of Aristotle.
All life forms can be arranged on a ladder of increasing complexity, each with its own rung.
The species do not change.
Humans are at the top of the ladder.
Taxonomy is the branch of biology concerned with naming and classifying the diverse forms of life.
He believed that a classification system would reveal a divine plan.
The naming system used today was developed by him.
Every organisms name consists of two parts, a genera name and a species name.
The scientific name of humans is Homo sapiens.
The man who died before Darwin published his thesis studied fossils and realized that the Earth is made of different fossils.
He believed that a series of events in the past were caused by mechanisms different from those in the present.
The changes in life on Earth were caused by these events.
Cuvier's study of fossils was very important in the development of Darwin's theory.
One of the most influential geologists of his day, James Hutton, published his theory of gradualism in 1795.
He said that Earth had been molded by gradual change.
The forces of wind, weather, and the flow of water that he saw in his lifetime were the same ones that formed the various geological features on Earth.
His theories were important because they were based on the idea that Earth had a long history and that change is normal.
Darwin's era had a leader in the field of geology.
Slow, continuous actions result in geological change.
He believed that the Earth was older than 6,000 years old.
The Principles of Geology was an influence on Darwin.
Lamarck developed a theory of evolution.
The year Darwin was born, he published his theory.
His theory is based on the idea of inheritance of acquired characteristics.
He said that organisms change in response to their environment.
According to Lamarck, the giraffe developed a long neck because it ate leaves from a tall tree for food.
The animals stretched their neck and passed on the trait to their offspring.
The theory was widely accepted in the early 19th century.
Alfred Russell Wallace wrote an essay about the process of natural selection that was similar to Darwin's work, which had not yet been published.
When he was 22 years old, Charles Darwin left England to visit the Galapagos Islands, South America, Africa, and Australia.
Darwin's theory of natural selection or descent with modification as the mechanism for how populations evolve was not published.
Maybe he was afraid of what his theories would do.
He published " On the Origin of Species" in 1859 after seeing a similar book by Wallace.
The traditional view of a young Earth inhabited by unchanging species was challenged by Darwin's theory.
Natural selection is a major mechanism of evolution.
reproductive success is a measure of evolution.
Populations tend to grow fast and overpopulated.
Malthus's work on population growth, disease, and famine was published in 1798.
There is variation in the ability of individuals to survive and reproduce.
The origin of variation in a population could not be explained by Darwin.
Only the best-fit individuals survive and get to pass on their genes to their offspring.
Evolution occurs when a population has certain beneficial qualities.
According to Darwin's theory, giraffes were short-necked and had different neck lengths.
The taller people had a better chance of surviving as the population of animals increased.
Until long-necked giraffes existed, the proportion of giraffes in the population with longer necks increased.
The insects don't become resistant to pesticides.
Some insects are resistant to a particular chemical.
The resistant insects have an advantage when the environment is sprayed.
The insects that are not resistant to the insecticide die and the remaining resistant ones breed quickly.
The new population is resistant to pesticides.
Natural selection toward resistance to insecticides is an example of directional selection.
At times of ecological stress, species extinction rates are rapid.
Natural selection can change the frequencies of inherited traits in a population in five different ways.
Five types of selection are stabilizing, disruptive or di versifying, directional, sexual, and artificial.
You should be able to describe a model that represents evolution.
Stabilizing selection eliminates the extremes and favors the more common intermediate forms.
Many forms are weeded out in this way.
The majority of birth weights are in the 3-6 pound range.
Infant mortality is higher for smaller and larger babies.
Young birds of the same species that lay a smaller number of eggs will have a larger clutch size than birds of the same type that lay a larger number of eggs.
Extreme types are increased in a population at the expense of intermediate forms.
A balanced polymorphism is when one population is divided into two or more different types.
The formation of two new species may be a result of disruptive selection.
Imagine that an environment with light rocks and dark soil is colonized by light, intermediate-colored, and dark mice.
The frequencies of camouflaged and dark mice would increase, while the intermediate-colored mice would die out.
Changing environmental conditions can lead to directional selection, where one phenotype replaces another in the gene pool.
There are two examples.
Biston betularia is an example of industrial melanism.
In England until 1845, most were light, but a few were dark.
Smoke and soot polluted the environment, making all the plants and rocks dark.
Only a few light-colored individuals could be found in the industrialized regions by 1900.
White and dark moths were easy prey for predator before the industrial revolution.
After the environment was darkened by pollution, dark moths were camouflaged and had an advantage.
The population of light moths was replaced by dark moths.
Rapid shifts in allelic frequencies can be produced by directional selection.
The discovery of antibiotics led to the emergence ofbacteria that were resistant to the drugs.
Scientists now know that the genes for antibiotic resistance are carried on small DNA molecule called plasmids, which can be transferred from one cell to another and which can spread the resistance very rapidly within the population.
The appearance of antibiotics does not cause resistance because it selects against the susceptible ones.
The next generation will be resistant since only resistant individuals survive to reproduce.
The experiment carried out by Joshua Lederberg proved that somebacteria are resistant to antibiotics.
Secondary sexual characteristics are related to competing for and attracting mates.
The evolution of horns, antlers, large stature, and great strength in males are the result of sexual selection.
The harem may consist of as many as fifty females.
Long canines are important for male-male competition in baboons.
Sexual dimorphism is the difference in appearance between males and females.
Birds colored in a way to blend in with their surroundings are more likely to protect their young.
The males have bright colors because they must compete for the attention of females.
The fitness of an organisms or a population can be increased or decreased by certain types of variation.
Humans breed plants and animals by looking for individuals with desired characteristics.
This is called artificial selection.
Racing horses and laying hens are bred to produce larger eggs.
Humans have bred a lot of vegetables from the wild mustard plant.
In order for a population to evolve as the environment changes, there needs to be variation in a population.
Darwin knew that variation exists in every population.
There are hundreds of breeds of dogs.
Canus familiaris is one species of dog.
Natural selection is thought to reduce genetic variation by removing unfavorable genotypes from a population.
There are eight mechanisms that preserve diversity or variation in a gene pool or population.
There are two or more distinct forms of a trait in a single population of a species.
The land snail's shells have a wide range of colors and patterns.
Banded snails are less visible than unbanded ones and therefore are less preyed upon.
Unbanded snails have an advantage in areas where the background is uniform.
Both varieties continue to exist despite the fact that each morph is better adapted in a different area.
There are two different types of rabbit in North America.
Rabbits in the cold, snowy north have short ears to conserve body heat.
Rabbits with long ears and mottled fur blend in with the surrounding woodsy areas to reduce body heat.
A graded variation in the phenotype of an organisms is known as a cline.
This is an example of a north-south cline because of the differences in rabbit appearance.
Sexual reproduction provides variation due to the shuffling of alleles.
During meiosis I, the exchange of genetic material of homologous chromosomes occurs.
The genes from two parents are combined to create individual chromosomes.
There are two or three events per pair in humans.
There are organisms that are not closely related that are outbreeding.
It is the opposite of inbreeding.
A strong genes pool and variation within a species are maintained by outbreeding.
If organisms that are closely related interbreed, they tend to have bad effects on the genes.
There are many mechanisms that promote outbreeding.