Oxygen, for one thing.
The Carboniferous period, during which oxygen amounted to 35% of the atmosphere by volume (this was around 300 million years ago). Nowadays the amount is 20.95%.
The Earth is about 4.5 billion years old and has had an atmosphere since it formed, but about 3.8-4.1 billion years ago there was believed to be the Late Heavy Bombardment, where a planetesimal roughly the size of Mars hit the Earth, breaking off a large chunk that formed into the Moon. This impact would have obliterated the atmosphere, but it has reformed naturally since then. So, the answer to your question is approximately 4 billion years old.
The composition of gases in the atmosphere has evolved significantly over the last 4 billion years. Initially, the atmosphere was primarily composed of carbon dioxide and nitrogen. Over time, organisms like cyanobacteria produced oxygen through photosynthesis, leading to the rise of oxygen levels and the formation of an oxygen-rich atmosphere. This transition enabled the development of aerobic organisms.
Ancient photosynthetic bacteria transformed the carbon dioxide atmosphere into oxygen through the process of photosynthesis. Over billions of years, these organisms released oxygen as a byproduct, eventually leading to the oxygen-rich atmosphere we have today that you breathe.
About the same. About a half billion years ago it was significantly higher, and more than a billion years ago it was lower, much lower. Before 1.5 or 2 billion years ago there was no free oxygen in the atmosphere, before 3 billion years ago there wasn't any.
The earths atmosphere has significantly altered over the years. The process of the earth's atmosphere was recognized and evolved 2.7 billion years ago, forming the nitrogen-oxygen atmosphere that exists today. This change enabled the formation and beginning of the ozone layer (which along with magnetic fields) block solar radiation.
There was no supercontinent back then. Earth is about 4.6 billion years old. It did not exist 5 billion years ago.
The first oxygen in Earth's early atmosphere was produced by photosynthetic bacteria around 3.5 billion years ago. These bacteria released oxygen as a byproduct of their metabolic processes, gradually increasing the oxygen levels in the atmosphere over millions of years.
The oxygen in Earth's atmosphere was likely produced around 2.4 billion years ago by photosynthetic organisms such as cyanobacteria, which released oxygen as a byproduct of photosynthesis. Over time, this oxygen accumulated in the atmosphere, leading to the development of an oxygen-rich environment.
The earths atmosphere has significantly altered over the years. The process of the earth's atmosphere was recognized and evolved 2.7 billion years ago, forming the nitrogen-oxygen atmosphere that exists today. This change enabled the formation and beginning of the ozone layer (which along with magnetic fields) block solar radiation.
In the first two billion years of Earth's existence, the atmosphere underwent significant changes. Initially, it was composed mainly of gases like carbon dioxide and methane, which created a greenhouse effect and maintained high temperatures. Over time, as photosynthetic organisms evolved and produced oxygen, the atmosphere gradually transformed into the oxygen-rich composition we have today.
The Earth's early atmosphere did not contain oxygen until about 2.5 billion years ago. Oxygen was produced by photosynthetic bacteria and later by plants as a byproduct of their metabolic processes. Over time, this accumulation of oxygen led to the development of the oxygen-rich atmosphere that we have today.