Reading

[1] The method of Radiocarbon dating was invented in the late 1940s by Willard Libby. It is a method to determine the age of an object by using radiocarbon properties. Radiocarbon is created in the atmosphere through the interaction of nitrogen and cosmic rays. When combined with oxygen, carbon dioxide is produced. CO2 enters plants through photosynthesis; animals and humans incorporate carbon when they eat plants. After the death of a plant or animal, the rate of carbon begins to decline – this is called the radioactive decay of carbon. When analysts measure the amount of carbon in this decayed object, they can calculate when it died. The furthest date that has been reliably measured back to is around 50,000 years.

[2] Research into the proportion of carbon in the atmosphere has been going on for more than five decades. Due to the increase in the burning of fossil fuels and nuclear testing in the 20th century, there was a significant increase in the level of carbon in our atmosphere, so this adds to the complication of carbon calculation. Originally, scientists used samples of solid carbon for testing. However, they realized that converting the samples to liquid or gas offered more precise results. Accelerator mass spectrometry is the current method of analysis. All carbon atoms in the sample are counted; its results are fast and very accurate.

[3] Archaeology has been profoundly affected by progress in radiocarbon dating. Faunal analysis has also been impacted by progress in this area. The faunal analysis is the study of the remains of animals with the aim to help us understand human activities in the past.

[4] At the end of the Pleistocene Era, there was much rapid extinction of megafauna, particularly in the Americas. There is a notable report by Vartanyan et al. on the extinction of pygmy mammoths, dating them back to 3700 years before the present using radiocarbon dating. Other scientists have used this method to calculate the age of the extinct species in the La Brea tar pits in California. In their faunal analysis, they employed a pre-treatment method that included the use of tar. They collected bones, divided them into small pieces and chips and crushed them. The bone fragments were treated with a variety of solvents, including benzene, to examine a species of Cuban Caribbean ground sloth and the Xenarthra armadillo. Carbon was then examined and radiocarbon dates were obtained from the organic material separated from the tar. Scientists were able to date the sloth remains to around 5400 before the present. This information is important as it may show that the extinction of the sloth was caused by human arrival in Cuba.

[5] Much work is necessary to further investigate the abundant fossil materials found in Central and South American pits, including those of Talara, Peru, where there are a lot of remains of extinct megafauna and human artifacts. Ongoing studies of these sites can help to verify the theories of extinction and its impact on human behaviour.

[6] One notable achievement in radiocarbon dating is Two Creeks, Fossil Forest. During the 20th century, a goal of geologists was to establish the date of transition from the Pleistocene to the Holocene era. The Pleistocene epoch began 2.6 million years ago and the current, Holocene period began 11,700 years ago. In Wisconsin, USA, a fossil forest called Two Creeks was discovered. Prior to radiocarbon dating, the trees in this forest had been dated back to around 24,000 years ago, the estimated date for the end of the Pleistocene period. This estimate had been made through correlation with sequences in Scandinavia. Libby and later scientists investigated Two Creeks and used radiocarbon dating to date the trees more accurately. Samples from the fossil forest were analyzed in over 70 labs, dating the trees back to 13,730 before the present. This achievement is now considered a notable result in the development of our understanding of glaciation in North America and the end of the Pleistocene epoch.

[1] Fossils give us a lot of evidence about the behaviour of extinct animals, reproduction and parental care. To discover dinosaur fossils, it’s important to find rocks of the right age. For example, in ancient rock exposures, we find only fossils of plants or marine organisms. In younger rocks, we find fossils of mammals, such as whales and horses. Palaeontologists can provide information on the exact age of rocks (225 to 65.6 million years old) that contain dinosaur fossils.

[2] Important clues of dinosaur behaviour include fossilized eggs and nests. There is evidence that dinosaurs took care of their babies after hatching from the discovery of skeletons of the theropod dinosaur Citipati. These skeletons were found in brooding positions which suggests that these dinosaurs were protecting their eggs. Bones of older babies in nests of the duckbill dinosaur Maiasaura were also discovered, along with a fossil of an adult Psittacosaurus preserved with the skeletons of tiny babies.

[3] Discovery of trackways suggests that some dinosaurs lived in family groups. These trackways are the prints of dinosaurs, of the same species, going in the same direction. Founded on these pieces of evidence as well as the behaviour of dinosaur descendants – birds and crocodiles – we know that dinosaurs took care of their young.

[4] Based on the studies of dinosaur skeletons, scientists understand that dinosaurs stood with their legs directly underneath their bodies, as horses and elephants do. For example, the sauropod dinosaur walked with huge, straight legs that had not yet adapted to running and jumping. However, Ornithomimid dinosaurs had long, skinny legs and Ostrich-like feet. These feet permitted them to run fast. The trackway evidence shows the actual movement of the dinosaur. We can estimate the speed of the animal and whether or not it used two or four legs. Other marks indicate how the dinosaur sat down.

[5] Fossils also give clues of the diet of our ancient predecessors. Scientists examine fossilized stomach contents to see what dinosaurs ate. The teeth and jaws can also give insight into feeding behavior and diets of dinosaurs. Dinosaurs with big muscles and huge jaws probably killed and ate large animals. The teeth vary from thin or sharp to large and thick. Similarities in the shape and type of teeth and jaws reflect a similar diet of a species. We can assume, from this hypothesis, that these dinosaurs were good at biting but their teeth did not allow them to chew very well. Scientists are beginning to understand which dinosaurs were meat-eaters and which ones were plant-eaters, based on their study of microwear (wear marks) on tooth enamel.

[6] Fossils of faeces are called coprolites. They consist of digested animal or plant tissues. A close study of these tissues gives information about the diet of dinosaurs. However, it is very difficult to identify the type of dinosaur with the coprolite and to associate the species of a dinosaur with its footprints. Nevertheless, scientists can narrow down the identities of dinosaur trackmakers by contrasting the foot size and shape, movement pattern and evidence of body size revealed by the trackmakers with other information about dinosaur species.

[7] For example, the front foot of an ankylosaur has five digits – or fingers – in an arch pattern. The organization of the hand bones and fingers has formed prints discovered in ancient rock. We know from skeletons that this type of hand or palm belonged to this species of dinosaur. Other dinosaurs have fewer ‘fingers’. From further evidence, scientists have also been able to identify some ankylosaur prints as nodosaur prints, common in the Early Cretaceous period.

[1] The earth’s atmosphere is a layer of gases surrounding our planet and retained by gravity. It warms the earth, regulates temperature between night and day and protects life by absorbing ultraviolet solar radiation. The atmosphere of Earth is a layer. Our atmosphere contains 78% nitrogen, 21% oxygen, 0.9% argon and .03% carbon dioxide.

[2] Earth is considered to have had three atmospheres. At first, the atmosphere was light, captured from the solar nebula made up of hydrogen and helium. A solar wind and intense heat drove off this first atmosphere. After, the earth released gases, creating a second atmosphere rich in water vapour, carbon dioxide, methane and nitrous oxide, but devoid of oxygen. Thirdly, an oxygen-filled atmosphere was formed once bacteria and living organisms appeared on the planet.

[3] The first atmosphere of the earth was formed from outgassing. This process occurred when gases trapped in the interior of the earth were released by volcanoes. During differentiation, the chemical change of magma during its cooling process, massive volcanic activity occurred on the earth which resulted in the emission of gases by volcanoes. This led to the creation of this early atmosphere.

[4] Early on, the atmosphere was mostly made up of water vapour which in turn transformed to rain and ocean. The result led to a reduction in carbon dioxide and an increase in nitrogen and oxygen. It is considered that this oxidation process was an important factor in the increase of atmospheric oxygen. Once this gas was produced, ultraviolet light split the molecules, creating the ozone UV layer. This allowed colonization on the land, as evidenced from plant life that appeared approximately 400 million years ago. Through the process of photosynthesis, oxygen formation increased further. This occurred in ‘The biological era’.

[5] The appearance of photosynthetic organisms, such as algae, had a major effect on the earth’s environment. Algae survived on carbon dioxide and released oxygen into the atmosphere. That oxygen was absorbed by banded rocks and red beds. Once those rocks became saturated, 1 billion years ago, they freed oxygen into the air. Oxidation of minerals on land transferred oxidized substances to rivers and oceans. Mineral iron deposits recently discovered in alternating layers are called Red Beds and date back to 2 billion years ago. After another billion years, these red beds became exhausted and oxygen began to increase in the atmosphere. This increase initiated the development of species diversification and cell development.

[6] Oxygen makes up 20% of our earth’s atmosphere. A question that continues to puzzle scientists is how organisms were not damaged by UV radiation prior to the production of oxygen. The oceans provided limited protection. It is believed that stromatolites – algal mats – protected organisms. Some scientists theorize that early organisms had a protective UV-absorbing case. In any case, microorganisms began to diversify thanks to natural selection.

[7] By the end of the Permian period, 250 million years ago, oxygen levels had fluctuated dramatically and then dropped to 15 percent. The rapid changes in oxygen caused a growth in insect size, but finally led to a mass extinction of giant dragonflies and other animals. When comparing Earth to neighbouring planets, we observe that Earth is at the ideal distance from the sun so that water could form through gaseous, liquid and solid phases.