The Origins of Life

Earth formation

4500 BCE

The history of Earth concerns the development of planet Earth from its formation to the present day. Nearly all branches of natural science have contributed to understanding of the main events of Earth's past, characterized by constant geological change and biological evolution.

The first organic molecules

4000 BCE

All living things consist of organic molecules, centered around the element carbon. Therefore, it is likely that organic molecules evolved before cells, perhaps as long as 4 billion years ago.

Life appears. Prokaryotic cells

3500 BCE

The first life on Earth came in the form of a prokaryotic cell. For two billion years prokaryotic cells were the only living things on Earth and spread to almost every corner of the planet. Today they are still the most abundant and diverse organisms on Earth and more prokaryotes are found in one handful of soil than all the humans that have ever existed.

Oxygen in the air.

1800 BCE

The atmosphere of Earth is the layer of gases, commonly known as air, that surrounds the planet Earth and is retained by Earth's gravity. The atmosphere of Earth protects life on Earth by creating pressure allowing for liquid water to exist on the Earth's surface, absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night (the diurnal temperature variation).

Fisrt eukaryotic cells

1400 BCE

The first, simplest life forms were prokaryotes—organisms, like bacteria, that don’t have a nucleus. Prokaryotes have existed on Earth since at least 3.8 billion years ago.
Eukaryotes are organisms with a nucleus. The oldest evidence of eukaryotes is from 2.7 billion years ago. Scientists believe that a nucleus and other organelles inside a eukaryotic cell formed when one prokaryotic organism engulfed another, which then lived inside and contributed to the functioning of its host.

Multicellular organisms. Cambrian life’s explosion

800 BCE

The Cambrian explosion or Cambrian radiation was an event approximately 541 million years ago in the Cambrian period when most major animal phyla appeared in the fossil record. It lasted for about 2045–2567 million years. It resulted in the divergence of most modern metazoan phyla. The event was accompanied by major diversification of other organisms.

Fisrt vertebrates

500 BCE

By the late Devonian, 360 million years ago, early cartilaginous fish and bony fish were diversifying. The late Devonian also marked the first tetrapods -- vertebrates with true legs that could walk on land. By about 330 million years ago, in the Mississippian, several groups of land-dwelling amphibians had appeared.

Dinosaurs and mammals coexist

200 BCE

When the dinosaurs ruled the world, the mammals hid in the shadows, daring to grow no bigger than shrew-like insectivores that hunted at night. Or so we thought. Two stunning new fossils from China have overturned this preconception. Not only did large mammals live alongside their giant reptilian cousins, but some were big and bold enough to go dinosaur hunting.

Dinosaurs’ extinction

65 BCE

SIXTY-FIVE MILLION YEARS ago, the last of the non-avian dinosaurs went extinct. So too did the giant mosasaurs and plesiosaurs in the seas and the pterosaurs in the skies. Plankton, the base of the ocean food chain, took a hard hit. Many families of brachiopods and sea sponges disappeared. The remaining hard-shelled ammonites vanished. Shark diversity shriveled. Most vegetation withered. In all, more than half of the world's species were obliterated.