The oldest meteorite fragments found on Earth are about 4.54 billion years old; this, coupled primarily with the dating … See more

The earliest identified organisms were minute and relatively featureless, and their fossils looked like small rods that are very difficult to tell apart from structures that arise through abiotic physical processes. The oldest … See more

Some biologists reason that all living organisms on Earth must share a single last universal ancestor, because it would be virtually impossible that two or more separate lineages could have independent… See more

Microbial mats are multi-layered, multi-species colonies of bacteria and other organisms that are generally only a few millimeters thick, but still contain a wide range of chemical environments, each of which favor… See more

Eukaryotes may have been present long before the oxygenation of the atmosphere, but most modern eukaryotes require oxygen, which is used by their mitochondria to fuel the production of ATP, the internal energy sup… See more

The defining characteristics of sexual reproduction in eukaryotes are meiosis and fertilization, resulting in genetic recombination, giving offspring 50% of their genes from each parent. By contrast, in asexual rep… See more

Animals are multicellular eukaryotes, and are distinguished from plants, algae, and fungi by lacking cell walls. All animals are motile, if only at certain life stages. All animals except sponges have bodies differentiat… See more