Earth Science Essay

The nature of biology is necessary to seek life in the early Earth and beyond the Solar System. The first step is to discover the nature of biosignature in those areas (to find remains or signs of previous or existing life). The earliest living things on Earth are assumed to be fossil microorganisms observed in warm water atmospheres where the hydrothermal vent precipitates appear (Dodd et al., 2017). Historically, biosignatures contain isotopic, chemical, and morphological proxies found inside the rocks. (Botta et al., 2008). These remains of old geological life in the rock and the formation of fossils are called fossilization. Fossils are conserved remnants or traces left by plants, animals, and other organisms in the past, which later become part of the Earth's crust (aimanb2, 2020). Appearances on the exterior of these organisms could stay intact under the most severe environmental conditions, such as biological decomposition, anoxic environment, rapid burial, and other situations. Over countless years, minerals and rocks take over the rest of the organism, resulting in a fossil as an end product.

The Earth is approximately 4.54 billion years old (Manhes et al., 1980; Dalrymple, 2001). There were two essential phases of the biosphere development process. Starting from ∼4 to 0.8 giga-annum (Ga=billion years), The biosphere was made up primarily of unicellular organisms (Steffen et al., 2016). In this early phase, there were many significant and improvements in the way the biosphere works, like the appearance that sulfur-reducing bacteria that are present (Grassineau et al., 2006; Wacey et al., 2011; Bell et al., 2015) and the development, which resulted in photosynthetic metabolic pathways (Grassineau et al., 2002; Payne et al., 2008; Allwood et al., 2009). One of the oldest undisputed proofs about life on Earth came from around 3.5 billion years ago (Schopf, 2006; Smith et al.,2015). Evidence of ∼0.8 Ga trace fossils, molecular (genetic), biomarkers, and fossil proofs helps describe how the biosphere evolves together with metazoans (animals). All this leads to Cambrian adaptive radiation (in other words, Cambrian explosion), preserving skeletal organisms in rock sequences around the world (Erwin et al., 2011). These deposits of fossils dating back 600 million years are further evidence of the significant changes occurring throughout the Earth's biota over the last decade and show how they interact strongly within abiotic features of our Earth system. However, sedimentary layers of the Cambrian and Neoproterozoic show first indications of mobile bilateral organisms (Jensen, 2003; Hou et al., 2004) being a part of the evolutionary continuity which gave rise to the most complex features of the trophic marine eco-systems in Phanerozoic times (Butterfield, 2011).

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[bookmark: _Hlk55847785]In general, fossils have two main categories: trace fossils and body fossils (Lutgens et al., 2011). Trace fossils or ichnofossils represent structures that are still intact in sedimentary rocks. It can serve as a record of biological activity to scientists that study them. Although trace fossils may not often be fascinating to look at, it is essential because they show anatomy as well as the behavior of the producer. Sedimentary structures of empty shells which roll on the bottom of the sea are therefore are not trace fossils as it does not display the creator's anatomy. Trace fossils comprise trace markings and tracks, footprints, coprolites, burrows, boreholes, and feeding tracks. The appearance of traces made from different wild animals can often seem very identical. Trace fossils are classified by the activity that produced them and not depending on the animal who created these: crawling, resting, housing, feeding, and so on. The most trace fossils have been produced by infaunal creatures, in particular by sedimentary eaters such as worms. Worm tracks in Cambrian sediments are quite frequent. Evidence of bird tracks in some places in the Utah and Green River Shales of Wyoming are also well known (museum, 2020). Body fossils: to allow fossilization to take place, all dead flora and fauna need to be buried fast while avoiding the risk of destruction caused by physical and biological factors. Then the processes that take place after burial involve compression, chemical changes, and substitution (WowEssays, 2020). The stages of fossilization processes are quite complex, ranging from the cover-up by earthly elements to the discovery of fossils. It is much more likely that organisms that have hard parts like mineralized shells, for instance, an ammonite or a trilobite, will turn into fossils. Animals that only have a body that is soft like a worm or jellyfish are unlikely to be fossils (museum, 2020). Body fossils are likely to be separated into groups of unaltered remains and altered remains (Raj, 2017).

Unaltered fossil remains are the original materials as well as tissues that were produced by the organism back then, while it was still alive. Such materials were left unchanged during geological time. Two types exist, they are unaltered mineralized remains and frozen remains. Whereas in these organisms, their soft parts disintegrated rather quickly after death, those hard parts of mineralized material that they built have generally remained intact, practically unaltered for millions of years. The use of such a form of preservation is quite commonly found and is particularly evident among a wide variety of marine invertebrates (organisms without an internal skeleton). Most of the bones are hard mineralized parts made of calcium phosphate, although the majority of fossilized bones show some changes due to the other minerals filling up their pore spaces. Some of the exceptions are geologically recent (Pleistocene) fossil bones found in places such as the renowned La Brea Tar Pits of Los Angeles, California. Since their owners had been alive, these bones retrieved out of the tar pits have hardly changed. Sometimes, some of the ancient Deoxyribonucleic acid (DNA) extracted out of the unaltered fossil bones gave representations of animals that became extinct, enabling scientists to gain a better understanding of evolutionary relationships with modern living beings. Frozen remains, it is possible to find fossils preserved in the ice. While the ice does not melt, these fossils might remain preserved for millennia or thousands of years. Massive fossils such as the woolly mammoth were likely to be seen in the Arctic glaciers (Ducksters, 2020). Those are ideal remains which are quite rare to find and also hardly any of them gets very old. Those fossils have retained their hair, bones, muscles, skin, and internal organs (museum, 2020). To any other form of preservation, the frozen remains enable a straightforward approach to the real soft tissues and occasionally to the organs which formed inside the body of an animal. Besides, some hair covers their bodies and show which color these animals had when they were still alive. In the Siberian permafrost, many species of frozen endangered species have been found, including wild beasts, horses, rhinoceroses, and woolly mammoths. Noticeable scientific discoveries are ongoing as the permafrost continues to melt in today's global warming climate (Hendricks, 2019).

[bookmark: _Hlk55847626][bookmark: _Hlk55778722]All the altered fossil remains are more likely to have been changed in one way or another: in a more or less complicated way, the material used to make the fossil was different from the materials used to make it during its life. Preservation of altered fossils may take various forms. Permineralization refers to a process of fossilization, which occurs to organisms that will be cover and buried. All the spaces that are empty inside the organism (Spaces that had gas or liquid throughout its life) get filled by groundwater that is rich in minerals. When minerals precipitate out of the groundwater, they occupy the empty spaces. However, this process can happen even though the smallest crakes, like within the cell wall of a plant cell. Small-scale permineralization is capable of creating highly detailed fossils. For permineralization to take place, organisms should be covered shortly after death by the sediment because it would decay if it is exposed. The limit to which these remains appear decayed when covered determines the details of the fossil later on. Some fossils contain only teeth or bone fragments; Different fossils include evidence of feathers, soft tissue, or skin such as diagenesis forms.

These original remnants left by the organism dissolve completely or can demolish by other means. Also, any remaining body-type holes in the rock are known as external mold. If this hole is subsequently full of other minerals, it is a cast. An endocast, or internal mold, is created when minerals or sediments fill the inner cavity within an organism, which could be the interior of a snail or shell or the hole of a skull head (Wikipedia, 2020). Replacement and recrystallization are a form of fossilization. Which is the rigid and high dense part of dead organisms that are weakened and slowly dissolved in water, will be replaced by minerals. Among the body parts preserved in this way are wood, tissue, bones, shells, and others. Many different chemical reactions take place for long periods during the replacement process. Their original body parts are broken down and progressively replaced with minerals such as hematite, silicic, pyrite, and calcite (WowEssays, 2020).

The shell is said to recrystallized if the parent compounds of the skeleton remain unchanged but should be in another crystalline form, such as aragonite in calcite. All coalified or carbonized fossils are likely to be made from organic waste, mainly as a chemical form of carbon (Wikipedia, 2020). Most of them are black, which reflects the presence of carbon (same as coal, which appears black). Carbonized fossil remains are the production that happens during the quick burial of organisms, most often under oxygen-deficient conditions. They can be thin, roughly two-dimensional films of carbon that remain intact at the surface of flat rock (Hendricks, 2019). Numerous ancient species are exoskeletons formed by geologically stable minerals such as aragonite and calcite. During compression, some fossil will compress with high pressure after debris. Fossils can create a dark imprint after this process, most common for fossils made of ferns and leaves but may also happen in other organisms (lumen, 2020). Full body fossils of insects amber found in the hardened sap of the tree, which is called amber, fossils like this can stay preserved in amber for millions of years (Ducksters, 2020).

The study of fossils helps us understand the evolutionary context, to study and reconstruct the history of the origin and extinction of different species that were present on our planet. Any remnant of the old life is a fossil. They can be body fossils, representing the remnants left by most organisms themselves, or other marks of activity done in the area. The preservation in the fossil state remains rare. The rapid burial and the appearance of well preserved hard parts, like shells or bones, increase the chance of fossilization. Fossil can be from in many ways by replacement, permineralization, compression, mold, and casts. Formations of rocks that have exceptional fossils are essential for research by scientists. These are fossils that exist widely, although barely for a little time. These are fossils that exist widely, although only for a short time. They are used by scientists to determine the age of a rock layer by comparing it to other layers of rock. These are organisms that have not changed enough over millions of years and are still alive today. Fossils provide information regarding our planet's life history, the evolution of the tectonic plates, the environment, climate, and other matters.