Lesson 2: Evidence for Evolution Flashcards
Evidence for Evolution- Age of Earth
The Earth is more than 4 billion years old. This was proposed by two geologists during Darwin’s time.
–>In 1788, James Hutton proposed that rocks, mountains, and valleys were continuously altered by weather patterns, as well as volcanic activity.
–>Charles Lyell (1830) agreed with Hutton and claimed that the ground is continually changing. The Earth’s surface is shaped by underground forces that twist and bend rock layers, bury others, and elevate some areas of the sea bottom to form mountains.
Fossils
Remains of ancient organisms discovered in rocks, silt, and stone.
–In the 1800s, geologists discovered fossils that differed from living organisms. The fossil record preserves the history of Earth’s species, although it is not complete.
Fossil Dating Techniques- Relative Dating 1
Scientists use this technique to compare the age of fossils in various layers of rock. Geologists were unable to determine the time it took for each layer to develop, limiting their knowledge.
Fossil Dating Techniques- Relative Dating 1: The Geological Time Scale
Scientists observed a consistent vertical order of layers of rock across different locations. Lower layers developed first and were older than the top layers. If the ground is not disturbed, scientists can estimate the approximate dates of the fossils.
Fossil Dating Techniques- Radioactive Dating 2
Rock contains radioactive elements that decay over time. Geologists can estimate a sample’s age based on its radioactive isotope content.
Fossil Dating Techniques- Radioactive Dating 2: Half-life
Geologists utilize “half life”to assess thesample age.
–>A radioactive element’s “half-life” refers to the time it takes for half of its atoms to decay.
Carbon-14 Dating
–Radioactive dating can accurately determine the age of once-living materials, such as bones.
–Carbon-14 is found in the atmosphere and absorbed by living organisms. When an organism dies, it stops absorbing carbon and decays into nitrogen -14. Scientists can identify a sample’s age by comparing its carbon-14 and nitrogen-14 content.
–Not reliable for samples older than 60000 years.
Two Problems with Fossil Evidence
- Fossils can reveal previous life, but only in sedimentary rock formations.
- Not all species are well preserved in fossils.
Similarities in Early Development
Embryos often look identical in their early stages of development.
Patterns of Variation
Populations evolve over time, therefore we may see several stages of change at any one time.
Darwin noticed this phenomenon in several groups, including finches.
–A common example for this is the peppered moth.
Similarities in Body Structures
The basic morphology: (body shape) appears to be similar in a variety of different species
Homologous Structure: Distinct parts of various creatures derived from the same ancestral body component.
->Example: human arm and fish fin.
Analogous structures share similar look and function, but have distinct origins and internal structures.
->For example, the wings of birds and insects.
Vestigial structures are non-functional parts of an organism, such as the small pelvis and thigh bones observed in whales and snakes.
Artificial Selection
–Selective breeding in domesticated animals demonstrates how selection can influence evolution.
–For thousands of years, humans have selectively bred specific animals. Domesticated animals now differ significantly from their wild counterparts.
–Humans have carefully bred and thereby heavily modifieddomestic animals for desired traits.
–While selection can lead to evolution, it does not imply that natural selection is the driving force behind it.
DNA Comparison
Comparison of DNA or RNA gives an indication of how closely “related” two organisms are and how recently they split from the same evolutionary path.
