Coelocanth: a fish from the Devonian period When was the Devonian period? Four hundred and sixteen million years ago, when the Silurian period ended and the Devonian period began, most of the land on Earth was clumped together into a supercontinent called Gondwana. Silurian period Plate tectonics All our geology articles Life in [...]
Kids eating food (thanks to USDA) - get ready to digest food! How do you digest food? When animals, including people like you, digest their food, they use an oxidation reaction to break down big hydrocarbon molecules like sugar into different molecules. Cell digestion Digestive system What is an oxidation reaction? All our chemistry articles [...]
Proteins are a type of molecule made mainly out of hydrogen and carbon atoms. They are combinations of smaller molecules called amino acids. The first amino acids probably developed into proteins more than four billion years ago on Earth, possibly with the help of ribonucleic acid, or RNA. We don't know whether this process has happened on [...]
A diagram of a sugar molecule found in outer space, from NASA Organic molecules means the kind of molecules that living things are made of - at least, all the living things we know about. All living things, both plants and animals, are made out of molecules that have carbon in them. Because [...]
A model of the amino acid molecule glycine (red is oxygen, black is carbon, yellow is hydrogen, and blue is nitrogen atoms) What are amino acids? Amino acids are molecules made out of hydrogen, oxygen, carbon, and nitrogen atoms (and a little sulphur). More about hydrogen What are molecules? All our chemistry articles When [...]
Diagram of a phosphorus atom Phosphorus atoms have fifteen protons and sixteen neutrons, so they're just a little lighter than sulphur atoms, in the middle of the range for atoms. Stars make phosphorus when two oxygen atoms get very hot and squash together into one phosphorus atom. All living things, both plants and [...]
Diagram of a carbon atom Where does carbon come from? When a star has changed all of the hydrogen atoms into helium, it begins to convert the helium atoms into carbon atoms and oxygen atoms. All of the carbon in the universe was made inside stars. More about stars What is hydrogen? Science [...]
Chalk cliff (made of calcium atoms) in Cottonwood Canyon, Pueblo, Colorado What is calcium? When a star is on the way to converting all of its carbon and oxygen atoms into iron, calcium is one kind of atom it makes along the way. More about stars And about atoms All our chemistry articles What's [...]
Children being vaccinated A vaccination is a way to keep animals (both people and other kinds of animals) from getting sick when viruses get inside their bodies. The earliest kind of vaccination was when people noticed that if you had already had the sickness and gotten better, you couldn't catch it a second [...]
The virus that causes AIDS (greatly magnified) HIV image copyright Russell Knightley Nobody is quite sure whether viruses are living things or not. The first living things may have come from viruses. But it's also possible that viruses evolved from living cells and got gradually less complex and more dependent on their hosts to live. [...]
