The atmosphere is an important part of what makes Earth livable. Our atmosphere today is made up of 78% nitrogen, 21%oxygen, and 1% other gases. High above the planet, the atmosphere thinner until it gradually reaches space. it is divided into 5 layers. Life and weather occur mostly in the first layer.
Triassic Period (252 to 201 million years ago) during this period the climate was relative hot and dry, and much of the land was covered with large deserts. It was in this environment that the reptiles known as dinosaurs first evolved reptiles tend to flourish in hot climates because their skin is less porous than mammal skin. Jurassic Period (201 to 145 million years ago) during this period at the end of the triassic there was a mass extinction many large land animals were wiped out but the dinosaurs survived, giving them the opportunity to evolve into a wide variety of forms and increase in number. Temperatures fell slightly, although it was still warmer than today due to higher amounts of carbon dioxide in the atmosphere. Rainfall increased as a result of the large seas appearing between the land masses. At the end of the Cretaceous period which was 65 million years ago a trillion ton asteroid, which is thought to have measured in with a 10km diameter, came crashing down to earth. This event which is called Chicxulub crater event caused massive tsunamis and global fire that killed living creatures on Earth at the time, including dinosaurs.
The reason why life nearly died is because the permian was devastating In the sea, the permian was the buildup of carbon dioxide and that changes in the greenhouse gases can kill nearly every creature on the earth the level of species loss was 80–96%, and blastoid echinoderms, tabulate and rugose corals, graptolites, trilobites, eurypterids, acanthodians and placoderms disappeared entirely. On land, the dominant Glossopteris flora was replaced, eight orders of insects became extinct and two-thirds of tetrapod families were lost. The only tetrapod lineages to survive were procolophonids, dicynodonts, and presumably therocephalians, cynodonts, and archosauromorphs, and their Triassic recovery was slow.
700 million years ago earth had these volcanoes in which they had emitted aerosols when the magma that eventually formed the Franklin LIP erupted to the surface, it shot particles of sulphur-rich sediments into the atmosphere as sulfur dioxide. This is a gas that absorbs solar radiation and it does this particularly well when it gets past the tropopause, the boundary between the troposphere and the stratosphere. At this height, there's a greater chance of it remaining in the atmosphere for a longer period of time, extending its presence from about a week to about a year, without being brought back down to earth in precipitation or mixed with other particles.
The first "pollution crisis" hit the Earth about 2.2 billion years ago. Several pieces of evidence -- the presence of iron oxides in paleosols (fossil soils), the appearance of "red beds" containing metal oxides, and others -- point to a fairly rapid increase in levels of oxygen in the atmosphere at about this time. Oxygen levels in the Archaean had been less than 1% of present levels in the atmosphere, but by about 1.8 billion years ago, oxygen levels were greater than 15% of present levels and rising.
The first traces of life started 3.5 billion years ago, in the early Archean. The oldest fossil that may represent a macroscopic organism is about 2.1 billion years old. Several types of fossil that appear to represent simple multicellular forms of life are found by the end of the Paleoproterozoic. These fossils, known as carbon films, are just that: small, dark compressions, most resembling circles, ribbons, or leaves; they are most common and widespread in the Neoproterozoic. Some resemble seaweeds and may represent eukaryotic algae; we know from independent evidence that red algae and green algae appeared in the Proterozoic, probably over one billion years ago.
A Lifeless Planet , when Earth formed 4.6 billion years ago from a hot mix of gases and solids, it had almost no atmosphere. The surface was molten. As Earth cooled, an atmosphere formed mainly from gases spewed from volcanoes. It included hydrogen sulfide, methane, and ten to 200 times as much carbon dioxide as today’s atmosphere. After about half a billion years, Earth’s surface cooled and solidified enough for water to collect on it.