In human beings, anaerobic organisms are usually found in the gastrointestinal tract. Some anaerobic bacteria produce clinically important toxins (e.g. tetanus).Energy metabolism Obligate anaerobes ma ...
Obligate aerobes need oxygen to grow. In a process known as cellular respiration, these organisms use oxygen to oxidize substrates (for example sugars and fats) and generate energy.Facultative anaerob ...
The division of the atmosphere into layers mostly by reference to temperature is discussed above. Temperature decreases with altitude starting at sea level, but variations in this trend begin above 11 ...
Air is mainly composed of nitrogen, oxygen, and argon, which together constitute the major gases of the atmosphere. Water vapor accounts for roughly 0.25% of the atmosphere by mass. The concentration ...
The RNA world hypothesis describes an early Earth with self-replicating and catalytic RNA but no DNA or proteins. It is generally accepted that current life on Earth descends from an RNA world, althou ...
Main article: Timeline of evolutionBased on recent computer model studies, the complex organic molecules necessary for life may have formed in the protoplanetary disk of dust grains surrounding the Su ...
Studies of strata, the layering of rocks and earth, gave naturalists an appreciation that Earth may have been through many changes during its existence. These layers often contained fossilized remains ...
All ordinary matter is made up of combinations of chemical elements, each with its own atomic number, indicating the number of protons in the atomic nucleus. Additionally, elements may exist in differ ...
The word medium comes from the Latin word medius (middle).The beginning of human communication through designed channels, i.e. not vocalization or gestures, dates back to ancient cave paintings, drawn ...
The first states came into existence as people "gradually transferred their allegiance from an individual sovereign (king, duke, prince) to an intangible but territorial political entity, of the state ...
List of states Short and formal names Membership within the UN System Sovereignty dispute Further information on status and recognition of sovereignty ↓ UN member states or observer states ↓ Abk ...
Phyllosilicates consist of sheets of polymerized tetrahedra. They are bound at three oxygen sites, which gives a characteristic silicon:oxygen ratio of 2:5. Important examples include the mica, chlori ...
Crystal structure results from the orderly geometric spatial arrangement of atoms in the internal structure of a mineral. This crystal structure is based on regular internal atomic or ionic arrangemen ...
Basic definition The general definition of a mineral encompasses the following criteria:Naturally occurringStable at room temperatureRepresented by a chemical formulaUsually abiogenic (not resulting f ...
A number of scientists have argued that the current global population expansion and accompanying increase in resource consumption threatens the world's ecosystem, as well as straining humanity's abili ...
