Option D Evolution

D.1 Origin of Life on Earth

Pre-Biotic Earth Conditions Conditions on earth that were beneficial to the beginning of life included high temperature, thunder and lightning bolts, penetration of UV light into the air, and a reducing atmosphere.

Miller and Urey Associates Miller and Urey conducted an experiment in 1953 to mimic the conditions of pre-biotic earth. They created a gaseous mixture based on predictions of pre-biotic conditions, and added an electrical charge. They were able to form basic biological molecules, such as amino acids, which could hypothetically synthesize into living organisms.

Early Replication Methods A hypothesis is that clay particles could have acted as catalysts by facilitating polymerization to form polypeptides. Once formed, RNA would be capable of self- replication.

RNA Replicators RNA is simpler than DNA and thus is a more likely candidate for earth’s initial replicators. It is also thought that early RNA acted as a substitute for what are now ribosomes. Later on, DNA would replace RNA as the primary genetic carriers.

Cell Origins Sheets of hydrocarbon molecules formed around those original primitive cells. Over time, the hydrocarbon protective sheet evolved into the role of a cell’s outer membrane.

Endosymbiotic Theory of Origin According to the endosymbiotic theory of origin suggests that at one time before the existence of eukaryotes, mitochondria and prokaryotic cells were independent. Outside cells similar to mitochondria were consumed and instead of being digested, a symbiotic relationship formed. The two work towards the common goal of a healthy eukaryote.

D.2 Origin of Species

Lamarck’s Theory of Evolution Lamarckian evolutionism, the inheritance of acquired characteristics, maintains that evolution is caused by traits consciously exerted by an organisms ancestors. Animals in their own lifetime respond to some survival need, and over time that need causes a physiological change. Example: Ducks spreading their toes wide to avoid sinking into mud over time develop webbed feet.

Backup for Lamarck Another example of Lamarckian evolution: a family of hoofed animals began to exhibit the behavior of stretching their necks to reach high leaves. Over many generations, the species developed a very elongated neck. It is the giraffe, of course. There is a strong lack of modern scientific evidence for Lamarckian evolution. Many experiments have shown that even if a test group is stimulated over many generations, no genetic change will occur.

Natural Selection Developed independently by both Charles Darwin and Alfred Wallace, natural selection claims that only organisms with the necessary survival characteristics will be alive long enough to pass on their traits to offspring. In this way, over time the weakest organisms will be weeded out of a population.

Special Creation and Panspermia Several other theories exist concerning the origin of life one earth. One of the most widely- held beliefs is that life was created by some divine being. Though popular, there is no evidence for this theory. Another possibility of life’s origin is panspermia, the theory of the arrival of organic material from outer space. Though space dust and other materials can be carried on a meteorite’s surface, panspermia has little scientific backing.

D.3 Evidence for Evolution

Geographical Evidence Many similar species are located in close proximity to each other geographically. Example: Marsupials are located in Australia. This fits with the theory of evolution that many different species evolved from one branch of the animal kingdom.

Petrified Remains Evidence of past organisms can be found in many ways. Many organisms can leave petrified footprints or imprints of their dead bodies in mud or soft soil. Small animals or insects can be preserved in substances such as amber, tar, or peat.

Fossil Dating Methods Scientists can determine the age of some rocks and fossils by measuring using specialized instruments the amounts of certain radioisotopes, most commonly, 14C and 40K. These isotopes have very specific half-lifes that can be used to backwards the age of the fossils.

Half-Life Half-life is defined as the amount of time necessary for a radioactive element to decay to one half of its original reactivity.

Radioisotope Decay Curve