Big Question: Where did we come from?
Unit Title: Scientific Theories of the Origins and Evolution of Life on Earth
3.1 Describe the main scientific theory related to the formation of the universe and of Planet Earth.
The following timescale for the early earth is the one accepted by most scientests.
* 13.7 billion years ago - The Big Bang and the beginning of the universe
* 4.54 billion years ago - The formation of the earth
* 4.52 billion years ago - The formation of the moon after the earth collided with a hugh object,
* Approx 4.5 to 4 billion years ago - The earth is constantly hit by meteorites from space.
* Approx 3.7 to 3.5 billion years ago - LIfe begins.
3.2 Describe the main scientific theories related to the origins and evolution of life on earth.
When did Life Begin? No-one can be certain when life first appeared on earth, but before 4 billion years ago the planet was being consistently hit by meteorites and this would have made it too hot. Many scientists believe that life first emerged in hot, underwater, volcanic vents. There is good evidence from fossils found in Western Australia that there were microbes in the ocean at least 3.5 billion years ago. This is not the only theory of the origin of life. Some scientists believe that life began on Mars before being carried to earth on space dust. These scientists are called astrobiologists.
Evolution explains how the many billions of different types of species of life that have ever existed developed over time.
Evolution happens when there are changes in the characteristics of a species over several generations. These changes are caused by mutations (changes) in the species DNA. Sometimes these changes make the offspring of an organism in some way better than before. Organisms with the mutation are then more likely to survive and reproduce then other members of the same species, perhaps because they are better at finding food, avoiding predators, attracting mates or resisting disease. This process is called natural selection. Over time this can lead to the development of new species.
3.3 Describe the evidence used to demonstrate the existence of different species of humans in the distant past.
All people alive today are Homo sapiens. We all belong to the same species. This is true no matter where we live, what we look like, what language we speak or what we believe and feel. Biologically, all people are essentially the same. All people alive today are also the descendents of groups of Homo sapiens that left Africa approximately 60,000 years ago. Once they had left Africa, Homo sapiens moved quickly into Asia, Australia and Europe. Between 10,000 and 20,000 years ago, Homo sapiens moved in the Americas.
Defining Homo sapiens
Before 1950, archaeologists could not be certain how old an object was. However, advances in the understanding of atoms led to the developing of radiometric dating. For example, all organic material, such as the remains of plants and animals, has two types of carbon - carbon 14 and carbon 12. Over time, the amount of carbon 14 reduces while the amount of carbon 12 remains the same. Scientists can then use the ratio of these two types of carbon to work out how old the object is to within about 100 years - even for objects tens of thousands of years old.
Carbon dating only works for organic materials and does not work at all for objects more than 50,000 years old. However, other techniques have been developed. For example, the relative levels of potassium and argon can be used to date rocks that are billions of years old.
3.4- Differentiate between the genera and species of humans that have been identified.
Homo sapiens were not always the only humans. 100,000 years ago Homo sapiens shared our planet with at least five other groups of humans. At that time, all Homo sapiens lived in Africa, along with a recently discovered group called Homo Naledi. Neanderthals dominated Europe and the western part of Asia, Denisovans lived in Asia along with Homo Erectus and at least two isolated groups that lived on islands: Homo floriensis and Homo luzonensis. All these other groups of humans disappeared at least 30,000 years ago.
However, the story of human evolution goes back much further than that. Between six and seven million years ago, on the edges of African forests, a new kind of primate emerged. This primate walked on two legs, which made it different from its closest relative, chimpanzees.
By 4 million years ago, various species of Australopithicus (or "southern ape man") had appeared in Africa. Like humans, they walked on two legs, but their brains were much smaller than ours. Australopiths had long arms and short legs. They were around three feet tall. For millions of years they made simple stone tools which they used to hunt or scavenge for meat. However, they also ate a variety of plants.
About 2.5 million years ago, the first members of the Homo genus appeared, once again in Africa. One of these, Home erectus, left Africa 1.6 million years ago and spread across Asia. Later, other forms of Homo, such as the Neanderthals and Denisovans evolved. They also left Africa. The Neanderthals mostly settling in Europe and the Denisovans in East and South Asia. There is good evidence that Neanderthals and Denisovans sometimes met and had children together. They also made tools, controlled fire and possibly made jewellery and created art.
The first Homo sapiens, the modern humans, appeared in Africa about 250,000 years ago. It is unlikely that they evolved from Neanderthals, Denisovans or Homo erectus and their exact ancestry remains unknown. Some scientists think that the Homo sapiens were the first, and only, species to develop true language. If so, then this gave them a big advantage over the other groups.
When Homo sapiens left Africa, about 65,000 years ago, they met Neanderthals, Denisovans and possible Homo erectus and Home floriensis. Some Homo sapiens had children with Denisovans and Neanderthals and most people living in Europe, Asia, Australia and the Americas today have some Neanderthal or Denisovan DNA.
Within a few thousand years of the arrival of Homo sapiens in an area, the other human groups disappeared. The reason for this is unknown, but the result is that the only type of humans left on the planet are Homo sapiens.
- 6 million years ago - Last Common Ancestor of humans and chimpanzees
- 4 million years ago - Emergence of the genus Australopithicus in Africa.
- 2.3 to 1.4 million years ago - Homo habilis existed in Africa.
- 1.9 million years ago - Emergence of Homo erectus in Africa. Homo erectus developed hand-axes.
- 1.7 million years ago - Possible date for the earliest human migration out of Africa to the rest of the world. The descendants of these early groups of migrating humans later became extinct.
- 400,000 years ago - Neanderthals lived in Europe. They went extinct about 40,000 years ago.
- 300,000 years ago - Evolution of Homo sapiens in Africa.
- 60-70,000 years ago - Homo sapiens migrated out of Africa and spread throughout the entire world. The spread of Homo sapiens was accompanied by the extinction of all other human species, including Neanderthals and Homo Floriensis.
The Smithsonian Museum website give details about all the known genera and species of humans. Click here to read more.
3.5 Describe how early humans used fire and developed tools and other technology.
* Fire - The earliest evidence of human-controlled fire, found in caves in southern Africa, dates to about 400,000 years ago. This was long before Homo sapiens evolved. Early human species, such as the Neanderthals, Homo habilis and Homo erectus probably first used fire to keep safe from animals such as big cats. Later they used fire to shape the landscape and as a tool in hunting large game, cooking and keeping warm. This, in turn, allowed early humans to move into new areas. Neanderthals would not have been able to colonize northern Europe without fire.
* Cooking with fire allowed early humans to eat a greater variety of food. It also made food easier to digest. Some archaeologists believe access to new types of food and easier digestion allow humans to evolve larger brains.
* Tools & Weapons
* Symbolic Art - Lines deliberately made by humans have been found in the Blombos Caves in South Africa dating from 70,000 years ago.
* Language - We do not know when hominids first developed language and we are not certain if language was unique to Homo sapiens. However, language must have already developed when the first Homo sapiens migrated out of Africa about 60,000 years ago.
* The use of boats
Some examples of technology developed in various parts of the world after 60,000 years ago are:
* Representational Art, for example pictures of animals and people painted on cave walls, which occurred 40,000 years ago in caves in France and Spain
* Bows and arrows were probably invented about 20,000 years ago.
* Systems of Weights and Measures - developed in western Asia, in the Indus Valley of Pakistan and in China.
* Money - The use of gold to represent value (that is as an early form of money) was used in Eastern Europe about 8,000 years ago.
3.6 Describe the spread of humans from Africa to the rest of the world, including how, when and why humans first arrived in, and then spread through, the Americas.
Published by Quality Assurance & Development Services, Ministry of Education, Youth and Sports, Belize. 2018