13.8 billion years ago the big bang and quarks began. Soon quarks joined together in threes to make protons and neutrons. 380000 years later the electrons joined to make atoms. Now the Universe was lots of gas. Gravity pulled it together to make stars. Big stars exploded to make rocks, gas, ice and dust. Gravity pulled some of this stuff together to make planets, moons, dwarf planets, asteroids, comets and more stars.
4.5 billion years ago the Earth was formed. In the beginning it was a ball of lava and gas. It was hit by another planet called Theia. The explosion formed the Earth and a ring of dust that later formed the moon.
The Earth was hit by millions of meteors. Some of them brought lots of water. When the Earth cooled down it started to rain and the ocean formed.
The first living things were like a bacteria that lived on the bottom of the ocean. They loved hot boiling water. These living things were called Archeae. Bacteria evolved from them. Some bacteria learned to use sunlight to make food. More complicated cells also evolved from Archeae. These complex cells, called eukaryotes, had lots of parts.
Some cells united by gluing themselves together. That helped them survive better as a team. Later some cells had special jobs. Some cells became muscles to make animals move, other cells became eyes. The first complex animals probably looked like sacks. Nobody knows what the first animals really looked like because fossils are rare before the Cambrian explosion.
The Cambrian explosion began 541 million years ago and lasted 55 million years. It probably happened because there was much more oxygen to help animals move faster. Many animals became preditors. Others had to defend themselves. Some evolved hard shells. Some developed spikes on their skin. Others evolved ways to swim away fast. The first fish had a spine but no fins and no jaw.
The next period is the Ordovician. In this period carbon dioxide in the air was much higher and sea levels rose. Simple plants like mosses started to invade the land. Some molluscs evolved two shells like clams. Other molluscs developed feet like the octapus. There was a mass extinction at the end of this period.
In the Silurian period many types of fish with jaws and bones evolved. Jaws helped fish to catch bigger animals. For some animals it was very dangerous. They had to evolve even more to escape jawed fish. Some fish developed fins like fans to swim faster. Other fish developed bones and muscles in their fins, maybe to get around in crowded shallow waters away from giant fast fish.
The Devonian was a very special period for fish. Many more types of fish evolved and they were the boss of the ocean. To escape from preditors some fish developed better kidneys so they can live in fresh waters like rivers, lakes and wetlands. Many more plants evolved including the first trees. The first amphibian evolved to escape from predators in the water and also to get more food from the land.
During the Carboniferous period Pangea was coming together. There were lots of land plants that made lots of oxygen that made insects huge. The first reptiles evolved. As some plants died they eventually turned into coal.
The Permian period was more dry so there were not as many trees and not as much oxygen. At the end of this period there was the biggest mass extinction ever and all the trilobites died. This is end of the Paleozoic era.
The Mesozoic era started 251 million years ago. The first period in this era was the Triassic. Lystrosaurus was the most common land animal with a back bone in the early Triassic. In the middle Triassic little dinosaurs existed. In the late Triassic more dinosaurs evolved. Some reptiles were evolving into mammals. There was a mass extinction at the end.
In the Jurassic period Pangea started to break apart into Laurasia in the north and Gondwana in the south. Many big dinosaurs evolved including Brontosaurus and Stegosaurus. The first bird evolved in the late Jurassic.
During the Cretaceous period Gondwana
broke up into South America, Africa, India, Australia and Antarctica.
Laurasia started to become North America and Eurasia. Tyrannosaurus rex
and Triceratops lived in North America. The climate was warm so the sea
level was high and there were lots of inland seas. There was a mass
extinction at the end caused by a big asteroid in Mexico 66 million
years ago. The only dinosaurs to survive were birds, crocodiles and
alligators. That was the end of the Mesozoic era.
The next era was the Cenozoic and we are still in this era. The first period of this era is the Paleogene. It started hot and humid then it got cold and dry. The sea level dropped by the end. India crashed into Asia to make the Himalayas. The age of the mammals began. In the beginning there were only tiny mammals. Later lots of different mammals evolved including primates.
The Neogene period started 23 million years ago. Giant sharks were the bosses of the ocean. Megalodon was the biggest and it is the most famous. Megalodons ate whales, orcas, smaller sharks and other large animals. At the end of the Neogene it was colder and the megalodon got extinct. During the period some monkeys started walking on two legs. The first primate to use tools was Homo habilis 2.8 million years ago in Africa.
Finally the Quaternary is the last period. It has two epochs; the Pleistocene and the Holocene. There were many ice ages in the Pleistocene. During each ice age a lot of the land was covered with ice and the sea level was very low so that there was more land and Australia was connected to Papua, and North America was connected to Siberia. There were many large mammals like mammoths, giant bears and giant kangaroos.
Homo erectus evolved 1.9 million years ago. They were the first hominid to leave Africa and spread to Asia. They used fire a million years ago. The next hominid to leave Africa was Homo heidelbergensis. They spread to Europe and Asia. In Europe they evolved into Neanderthals, in Asia into Denisovans, and 250 000 years ago in Africa they evolved into Homo sapiens.
75 000 years ago a huge volcano erupted in Sumatra. It formed ash in the air over the whole world. The sunlight was blocked and the Earth was colder. Humans were nearly extinct. There were only about 2000 people 70 000 years ago.
(to be continued)