Earth, or Tellus as we call the planet, consists of and is surrounded by four major spheres: the atmosphere, hydrosphere, lithosphere and biosphere.
The sun plays a central role in these spheres, and life on Earth would not exist without its light and heat. In addition to warming the atmosphere and the Earth’s surface, the sun’s energy drives the water cycle, wind circulation, ocean waves and plant photosynthesis [1].
THE ATMOSPHERE
The atmosphere, the surrounding air around Earth, is stratified into distinct layers: the troposphere, stratosphere, mesosphere, thermosphere, and exosphere, arranged from bottom to top. At the centre of the stratosphere, a crucial element is the ozone layer. This layer plays a vital role by absorbing and scattering the sun’s UV radiation [2]. The atmosphere consists mainly of 78 % nitrogen and 21 % oxygen [3]. It also contains water vapour, which varies between 0-4 % [4].
Greenhouse gases, including carbon dioxide, methane, argon, and neon, make up a small proportion of the atmosphere. Carbon dioxide (CO2) constitutes about 0.04% of the atmosphere’s composition [4]. Despite their minimal presence, these gases can have a substantial impact on the temperature of the atmosphere. The absorption of sunlight by the Earth leads to global warming. As the surface warms, it releases energy from infrared radiation (heat) into space.
Water vapour and CO2 act as a ‘lid’, making it harder for the Earth to eliminate this energy. Without these gases absorbing the energy, there would be much more significant temperature differences between day and night [5]. Compared to the size of the Earth, the vital atmosphere is no thicker than the skin of an apple.
The word atmosphere comes from the Greek atmos = vapour and sphaira = sphere or ball.
THE LITOSPHER
The lithosphere is the crust and the upper part of the mantle. The Earth is divided into different layers, with the lithosphere being the solid surface, about 100-150 km deep. The mantle extends from 10-70 km to 2890 km deep and is divided into several layers. The core is the inner part [6].
We then divide the Earth’s crust into seven major plates and about ten smaller ones. The seven major plates are the North American, South American, Eurasian, African, Indo-Australian, Antarctic and Pacific. These ‘puzzle pieces’ slide around on top of the mantle thanks to heat from the Earth’s interior, moving relative to each other at a rate of a few centimetres per year [7]. These create dynamics and changes in the Earth’s surface and contribute to the carbon cycle by feeding carbon deposited in the crust to the depths where it eventually comes back up with the volcanoes. This mechanism is necessary for life to take root and develop on Earth.
Within the lithosphere, there is also something called the pedosphere. The pedosphere is the thin soil layer and organic matter covering the Earth’s surface. Within this thin layer, plants live and grow, and animals such as deer, sheep, and cows feed on these plants. It is also where small animals such as grey owls, worms and micro-organisms break down organic matter into soil. The pedosphere is especially important because it interacts with the biosphere, supporting plant life and playing a key role in nutrient cycles and ecosystems.
The word lithosphere comes from the Greek líthos = stone, and sphaira = sphere or ball.
THE HYDROSPHERE
The hydrosphere is about all the water on Earth. This means all the water found in oceans, lakes, rivers, groundwater, ice, snow, glaciers and whatever form it takes: liquid, frozen or vapour (gas). The biosphere also includes water bound up in life, such as the water in plants, fungi and animals [8]. To learn more about the water cycle, click here: Water Cycle 
or for younger children: Learn Bright – the water cycle
The frozen water on the Earth’s surface, such as snow, glaciers, ice sheets and permafrost, is called the cryosphere and is part of the hydrosphere. This frozen water plays an essential role in regulating the Earth’s temperature, influencing sea levels and reflecting solar radiation, and is therefore also important for the climate. The temperature and composition of the atmosphere affect the cryosphere by regulating melting and freezing. Meltwater from the cryosphere can affect the hydrosphere’s volume, temperature, salinity and sea levels.
Saltwater accounts for the largest share, almost 97.5 % of the Earth’s water. The remaining 2.5 % is freshwater, i.e. so-called fresh water. Freshwater is essential for drinking, growing, washing, etc. In principle, all terrestrial life on Earth needs fresh water to exist.
For example, we cannot water the cotton fields with salt water; the plants grown need fresh water. Of the small amount of freshwater, more than two-thirds (68.9 %) is ice in the form of glaciers. One-third, about 30.8 %, is groundwater, and less than 1 % (0.3 %) is found in lakes, rivers, etc. This thin slice is what most terrestrial life in the biosphere has to share: humans together with other animals, plants, fungi and bacteria. In Sweden, we are fortunate to have many lakes, over 100,000, which make up about 9 % of Sweden’s surface area [9].
The word hydrosphere comes from the Greek hydros = water and sphaira = sphere or ball.
THE BIOSPHERE
The biosphere is all life, i.e. life in the atmosphere, lithosphere and hydrosphere—the biosphere is one huge global ecosystem. Numerous ecosystems exist at all levels (10). For example, the forest has its own, but trees, mosses, ants and humans also have small ecosystems. The lake is an ecosystem in itself, which in turn is divided into smaller parts, such as the seaweed, the fish, the frog, etc. The garden has its ecosystem with different components, such as the bush, the grass, the beetle and the worm. There are even ecosystems inside and on different organisms, such as your skin. Diverse ecosystems have other food chains and nutritive webs.
We divide the living world into different categories: animals, plants, fungi, microorganisms, bacteria, archaea and protists. They all live together in ecosystems where they depend on and influence each other. Animals are dependent on the energy that green plants bind by capturing sunlight through photosynthesis. This energy travels up the food chain as larger life forms eat smaller ones. Fungi, small animals and bacteria then break down dead organic matter, which becomes new food for the plants again. This interaction between all of life is fascinating.
The word biosphere comes from the Greek bios = life and sphaira = sphere or ball.
Sources
- Kaufmann & Cleveland (2008) – Environmental Science: The Physical Systems of Planet Earth
- Rymdstyrelsen – What is the atmosphere and what are its parts?
- SO-rummet – The atmosphere, clouds and winds
- Columbia Climate School – CO2 Is Only 0.04% of the Atmosphere, How Does it Drive Global Warming?
- Naturvårdsverket – The greenhouse effect is enhanced
- Geologica.fi – The asthenosphere and the lithosphere
- Naturhistoriska riksmuseet – Plate tectonics and continental drift
- Renovables verdes – What is the hydrosphere?
- Artdatabanken – Lakes and waterways
- Nationalencyklopedin – The biosphere
Download the page as a pdf by clicking on this image.
