Combs, EmilyBiology, Period 3Due date: December 6thImagine being on a burning hot planet covered in magma and rocks. That’s what life on Earth was like about 4.6 billion years ago. In this essay I will prove how life on Earth started and adapted as the Earth’s atmosphere changed. I will do this by showing how Earth’s atmosphere developed and life evolved along with it, along with introducing a popular theory as to how life itself started. Let’s explore how much our planet has changed in its billions of years of existence.Earth’s atmosphere went through a lot of changes. 4.6 billion years ago, meteors and comets smashed into our planet. Due to the volcanic activity and heat, magma evaporated and created a thick layer of steam over our planet (Bighistoryproject. YouTube). This was what formed Earth’s first atmosphere. As our planet’s crust was formed and it cooled, the water vapor condensed into oceans (Bighistoryproject. YouTube). With water now on the surface of the planet, other molecules such as carbon dioxide and methane made up our atmosphere. With carbon dioxide being available in such large scale, single celled bacteria started photosynthesizing and pumping out oxygen as a waste product (Marshall, 1). With oxygen in our air, the planet started changing into the Earth we know today. Let’s go back and see how this allowed organisms to evolve. Early organisms had a great influence on the Earth’s atmosphere. Microbes would use methane as a food source (Where Did We Come From? PBS). This proves that certain single cellular life forms could live in the Earth before oxygen was in its atmosphere. Of course, oxygen was added and made a great impact during the Great Oxidation. Cyanobacteria started using oxygen as a waste product (Marshall, 2). The bacteria are what we believe to be the oldest organisms to add oxygen into our atmosphere. The oxygen that was being added to the air allowed bacteria to evolve and become more complex. Bacteria could become multicellular and move around, spreading themselves onto rocks to make sure they don’t get washed away (Marshall, 3). More organisms started photosynthesizing and releasing oxygen into the atmosphere, adapting to the changes and using oxygen to their advantage. There is still one question that everyone wants to know. How did life begin? To this day scientists don’t have a definitive answer, but there are theories to answer the question. I will be focusing on Panspermia. As I addressed earlier, meteors and comets smashed into the Earth and brought us molecules (Origins of Life: The Panspermia Theory. Helix Magazine). An example of a molecule that could be carried on a meteor is carbon, the most important molecule in life. Carbon is used in many ways on Earth, such as to make glucose and energy, or trapping heat in our planet as carbon dioxide. Bacteria, organisms that are thought to be the first life forms on Earth, can survive in the most extreme conditions. (Where Did We Come From? PBS). That could prove how they survived the heavy bombardment era our planet had in its early years. Another detail that supports this theory is that amino acids have been found on meteors. Amino acids are the building blocks of proteins, which are important for all living things. A test was done where scientists recreated the impact amino acids would have when they hit the Earth on a meteor (Where Did We Come From? PBS). The scientists found that the amino acids survived the crash and turned into Peptides. Peptides can be used as chemical messengers or hormones (Mor, Amrarm). The only thing that refutes this theory is that it doesn’t explain how exactly life started in space. The first organisms and atmosphere coevolved over the billions of years they have existed together. The Earth’s atmosphere evolved along with the first life forms over a long period of time through photosynthesis and heavy bombardment by meteors and comets. Life is a mystery that may not ever be solved, but we can get close if we continue to research and look back to our planet’s past.