Evolution Notes (9th Grade H)

Evolution

Concept of Evolution

• Concept that species change over time.

Main Points of Evolution

• The characteristics of each species do not remain the same forever.

• The changes are linked to mutational changes within the gene pool.

• “Mother Nature” selects in favor of those traits that are best within the population relative to their environment at the time.

• Life has generally evolved from simple life forms towards more complex and diverse life forms over time.

• The amount of changes that are believed to have occurred within species would require vast amounts of time, indicating that the Earth must be very old.

Establishing the Age of the Earth

Scientists and common people alike have pondered the question of the age of the Earth. Theologically or from a religious perspective, many believe that the Earth is approximately 6,000 years old. This belief is based primarily upon the work of three men during the 1700s:

1. DeVignoles (1738): Estimated the Earth to be approximately 5800 years old based upon biblical readings and ancient Egyptian references to time and the creation of man.

2. Bishop James Ussher: Declared the Earth to be 6000 years old based upon similar work to DeVignoles, calculating it as 6 PM on 22 October 4004 BC.

3. John Lightfoot: Took a more structured approach to calculating time through biblical readings, declaring that God created the Earth on October 23, 4004 B.C. at 9:00 a.m. Ussher is the best known of the three men and gets most of the credit for this “Young Earth Theory”.

Scientifically Determining the Age of The Earth

Scientists generally took two approaches to measuring time and the age of natural materials, including the Earth itself:

Relative Dating

• Determining the relative age of materials by comparing their positions instead of actual time.

Law of Superposition

• States that in layers or strata of rocks, the oldest layers and materials will be on the bottom and the youngest materials on the top.

Absolute Dating

• This method attempts to determine the true age of a material, usually involving radioactive dating methods.

Radioactive Dating

• Each radioactive isotope undergoes a process known as radioactive decay. In this process, the atoms release energy at a very steady and precise rate, eventually transforming into a different element.

• Half-Life: Each radioactive isotope decays at a precise rate known as its half-life. This duration is when exactly one half of the original quantity will complete its decay.

The Age of The Earth

The oldest rocks found on Earth include several zircons found in western Australia, dating to approximately 4.4 billion years old. Moon rocks, including meteorites, also date to around 4.5 billion years old. Scientists are confident that 4.6 billion years is an accurate estimate of the age of the Earth.

Better Evidence

Better evidence for establishing the age of the Earth comes from determining the age of the entire solar system:

• Meteorites: Rocks that reach the Earth’s surface from space, primarily found in Antarctica where they remain well-preserved, consistently date to approximately 4.6 billion years old.

• Scientists believe the Earth itself was older due to extreme heat during its early history known as the Hadeonic Earth.

Radiometric Dating of Fossils

All living things are primarily composed of organic compounds, which all contain carbon. A small percentage of that carbon is a radioactive isotope known as Carbon-14, which decays into Nitrogen-14 with a half-life of approximately 5730 years.

Dating of Fossils

• Fossils are typically dated by studying the decay of Carbon-14, but this method is effective only up to about 50,000 years.

• Beyond this, other radioisotopes are used to date the surrounding rock:

  1. Uranium-Lead (U-Pb)

  2. Potassium-Argon (K-Ar)

  3. Rubidium-Strontium (Rb-Sr)

Explaining the Origins of Life

The Coacervate Theory

Proposed by Alexander Oparin (Russian), he suggested that Earth’s early atmosphere and oceans were vastly different from what we see today:

• Atmosphere: Methane (CH4), Hydrogen (H2), Ammonia (NH3), Water Vapor (H2O)

• Current Atmosphere: Nitrogen (N2), Oxygen (O2)

Oparin’s Beliefs

• The early atmosphere was volatile, with fast-moving particles becoming heavily charged with electrical energy. After cooling, the resulting water vapor formed oceans with rich combinations of molecules, dubbed “organic soup.” Within that soup, coacervates could form.

Harold Urey (professor at the University of Chicago) and Stanley Miller (graduate student) tested Oparin’s theory, with experiments producing coacervates and simple organic molecules.

Evidence to Support Evolution

1. Geological and Fossil Record: Life is believed to have begun about 3.5 billion years ago. The fossil record shows a clear progression in diversity and complexity.

2. Vestigial Organs: Structures within species with no apparent function today (e.g., human appendix, tailbone, etc.), indicating evolutionary change.

3. Homologous Organs: Similar anatomical forms that differ in function (e.g., mammalian forelimb structures).

4. Analogous Organs: Organs serving similar functions but different in structure (e.g., bat wings vs bird wings).

5. Genetic and Biochemical Similarity: DNA analysis allows comparison of species, highlighting similarities in biochemical pathways.

6. Similarities in Early Development: Related species exhibit similarities in early embryonic development (e.g., gill slits, tail buds).

7. Ongoing Population Studies: Monitoring existing populations for changes in gene frequencies indicates patterns of evolution.

Lamarck’s Theory of Evolution by the Acquisition of Traits

Jean Baptiste Lamarck developed the first formal theory of evolution summarized in three sub-theories:

1. Theory of Need: Organisms change based on needs created by environmental pressures.

2. Theory of Use/Disuse: Traits can be altered through behavioral influences (i.e., “use it or lose it”).

3. Theory of Acquiring Traits: Altered traits can be inherited by offspring.

Alfred Russel Wallace

A British naturalist who observed similar species during his travels through South America and later Malaysia, leading to corresponding thoughts on evolutionary theory with Charles Darwin.

Charles Darwin (1809-1882)

British naturalist and ship’s naturalist aboard the H.M.S Beagle. In 1859, he published On the Origin of Species, detailing:

• Original Theory: Evolution by natural selection, developed jointly with Alfred Russel Wallace.

Major Points of Darwin’s Theory

• Overproduction: More offspring are produced than can survive.

• Variation: Individuals naturally vary.

• Struggle to Survive: Constant competition for resources determines fitness.

• Natural Selection: Favorable traits are inherited by survivors.

Scopes Trial

In the 1920s, John Scopes was tried for teaching evolution in Tennessee, implicating not just himself but also First Amendment rights with William Jennings Bryan as prosecutor and Clarence Darrow defending him. Scopes was found guilty and fined $100.

Punctuated Equilibrium

An expansion of natural selection theory indicating species experience long periods of stability interrupted by rapid changes due to catastrophic events, influencing evolutionary paths.

Factors That Influence Natural Selection and Evolution

• Mutation: Introduces inheritable genetic variations into a population.

• Migration: Movement of individuals into or out of populations, altering gene pools.

• Isolation: Separation affects evolutionary trajectories.

Patterns of Evolution

• Divergent Evolution (Adaptive Radiation): One species evolves into multiple; showing homologous characteristics.

• Convergent Evolution: Unrelated species adapt similar traits through environmental needs, shown by analogous characteristics.