In the solar system, the Earth is the third planet from the sun, and it is the only planet known to have life. According to different sources of evidence like radiometric dating, the Earth is believed to be more than 4.5 billion years old. Out of the four terrestrial planets, the Earth is the largest and densest planet. The lithosphere is made up of numerous tectonic plates that keep moving over millions of years. Water in the oceans cover about 71% of the total surface of the Earth, and the remaining 29% is covered by the continents and islands, which have rivers and lakes. The ability of the Earth to harbor life makes the Earth a unique planet in the solar system, and this stems from the fact that water in liquid form exists on the planet. Similarly, the existence of gaseous oxygen in the atmosphere of the Earth also supports life.
Evolution Of Life On Earth
It is believed that about 4 billion years ago, a chemical reaction was triggered which led to the first self-replicating molecules. Later, about half a billion years ago, the last common ancestor of all the present life forms arose. Photosynthesis evolved to allow the energy of the sun to be harvested, and the resulting oxygen accumulated in the atmosphere. The interaction between the oxygen and ultraviolet radiation from the sun led to the formation of the ozone layer, which is a protective layer in the atmosphere. The most important step was when the smaller cells were incorporated within larger cells leading to the development of larger and complex cells of eukaryotes. Multicellular organisms were formed when colonies of cells became more specialized.
According to some planetary geologists, the Martian surfaces have certain features that could indicate the planet may have had some active volcanoes in the past, particularly during its early phases when it was formed. Other than this possibility, which remains to be confirmed, no other planet in the solar system other than the Earth has tectonic plates. In this regard, the Earth is unique among the planets in the solar system due to the tectonic plates which are constantly moving because they are being driven by the convective loops of hot rock in the core. The lithosphere on our planet is divided into different tectonic plates, which move relative to each other at one of the three types of boundaries. At a convergent boundary, the plates shift towards each other, at divergent boundaries the plates move in the opposite direction away from each other, and at the transform boundary, the plates shift laterally past each other. A lot of activity occurs along these tectonic plate boundaries and they are associated with the formation of oceanic trenches, mountains, volcanic activity, and earthquakes. Currently, there are seven main tectonic plates, and they include the Pacific, South American, African, Indo-Australian, Antarctic, North American, and Eurasian. Other smaller plates include Scotia Plate located in South Atlantic Ocean, Nazca Plate which is found in the west coast of South America, the Caribbean Plate, and the Arabian Plate.
Origin Of Oxygen On Earth
The Earth is the only planet in our solar system that has oxygen in gaseous form. In its formative years, the Earth had an oxygen-free atmosphere, and it took several millions of years before oxygen was sufficient to keep organisms alive on our planet. Initially, the Earth's atmosphere was made up of nitrogen, methane, and carbon dioxide. The rays from the sun were able to split carbon dioxide to free some oxygen and other molecules. During this early period, the oxygen created would disappear as soon as it was formed because of the ability of oxygen to form bonds quickly with other molecules. For instance, it would bond with hydrogen from volcanoes to form hydrogen peroxide among other compounds. About 3 billion years ago, the Earth's atmosphere had about 0.03% of the current oxygen levels in the atmosphere. At this time, some microbes had evolved and were able to carry out photosynthesis and generate oxygen.
The Earth's Biosphere
Different life forms on Earth inhabit different ecosystems and all ecosystems form the biosphere. The biosphere on Earth is divided into different biomes, and it is believed to have evolved over billions of years. On land, biomes are typically separated by humidity, height above sea level, and latitudes. Broadly similar animals and plants inhabit the same biome. A biosphere can be referred to as a zone of life on the planet Earth, and it is almost self-regulating.