Coelocanth 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. At this time the only creatures that lived on land were small plants like moss and lichens, mushrooms, and other fungi, [...]
Kids eating food (thanks to USDA) 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. In order for your cells to break down sugar molecules made of hydrogen and carbon atoms, they have to combine the sugar with oxygen, just [...]
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) Amino acids are molecules made out of hydrogen, oxygen, carbon, and nitrogen atoms (and a little sulphur). The earliest amino acids formed in space, about 14 billion years ago, before our solar [...]
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 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. Carbon atoms are heavier than helium or hydrogen, because they have six [...]
Chalk cliff (made of calcium) in Cottonwood Canyon, Pueblo, Colorado 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. One atom of calcium has 20 protons and 20 electrons (and 20 neutrons). Calcium is a [...]
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. [...]
