They believe based on experiments done my Stanley Miller and Harold Urey that the early oceans had tons of organic molecules floating around and the energy from lightning and UV rays converted these molecules into macromolecules such as amino acids and nucleotides. Then protobionts which have some life like characteristics may have formed they would be contained in a membrane and maintain a separate composition from their surroundings. Eventually amino acids were able to form ribosomes and RNA was used as the first genetic material. Ribosomes that were able to self-replicate would be naturally selected for and therefore the environment would give rise to a genetic code.
How is the Fossil Record used for information about living things?
The fossil record is mostly used to date organisms and the arrival of different species as well as by seeing them in chronological order enables scientists to guesstimate which species are descendents of other species. It also allows them to study at least the remnants of species that went extinct and see how creatures were adapted to the world as it used to be. They can date fossils either relatively by the position the strata that they are found but this only shows the age of fossils in relationship to other fossils. To get a more accurate age of fossils radiometric dating is used. Basically by using the half-life (time it takes for half the isotope to decay) of the isotope and then comparing it to the amount left in the fossil a more accurate age is given.
What is Adaptive Radiation and what causes it?
These are periods of sped up evolutionary change to fill new environmental needs. After each of the five major extinctions a mass adaptive radiation has occurred. The mammals underwent an adaptive radiation after the dinosaurs went extinct the mammals had to become more diverse to fill the ecological roles the dinosaurs had before. Adaptive radiation can also occur on a small scale usually when organisms settle in a generally desolate land they then undergo large structural changes and such to fill up to the uncharted land. Basically large changes of species occur when there are ecological niches not being utilized so larger behavioral or structural changes occur to take on these roles.
Facts:
- About 250 million years ago all the land masses on earth were connected they form Pangaea this new environment killed off many species but also gave rise to new ones it also accounts for fossils of the same species now found in lands separated by the ocean
- 2.7 billion years ago oxygen started to become present on the earth giving rise to species that utilized respiration
- The first eukaryotes came to be 2.1 billion years ago scientists believe this was due to endosymbiosis where smaller organisms were engulfed by larger ones and the symbiotic relationship is the reason for organelles
- The accumulation of O2 in the earth’s atmosphere about 2.2 billion years ago led to organisms that utilize respiration
- The arrival of creatures with totally different body structure than their ancestors is a result of change in DNA sequence and regulatory genes becoming inactive allow the display of different genes
This shows how human and chimp skulls are very similar during the fetal stage but chimps’ skulls continuing elongating where humans stop. This is an example of how changes in genes that control growth and development when altered can make large differences in the anatomy of a creature and therefore lead to macroevolution and new species.
Summary:
The early atmosphere of the earth was rich with organic molecules these gave rise to macromolecules such as amino acids and nucleotides. Once protobionts that maintained a different chemical composition than their surrounding arose Rna became a method for passing along genetic info it was later replaced by DNA because it had less error. The fossil record shows us animals of the past ect and they are dated by radiometric or relative dating. The first organisms were prokaryotes then eukaryotes became prominent with the addition of O2 organisms became more diverse and once organisms colonized land they underwent even more diversification. Large groups of organisms have come to be and gone extinct long before humans were even on the earth these major events were due to continental drift and large changes in environment or natural disasters that led to mass extinctions, to recover from this the organisms left have undergone adaptive radiations. Major changes in organisms physical structure is often due to changes in regulatory genes and developmental timing and patterns. Evolution has no desired result so the trends for evolving vary based on the environment as organisms try to make the best out of their ecological niche.
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