Unit Three Origins

BIG QUESTION: Where did we come from?

Scientific Theories of the Origin and Evolution of Life on Earth

Subtopics
From the Big Bang to Humanity
The emergence and dominance of Homo Sapiens

3.1 Describe the main scientific theory related to the formation of the universe and of Planet Earth.

In 1927, Georges Lemaitre proposed that the universe started as a single point and that it has since expanded to the size it is now.

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.

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.

Learning Outcome 3.2 - Describe the main scientific theories related to the origins and evolution of life on earth.

What is Evolution?
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.

Learning Outcome 3.3 - Describe the evidence used to demonstrate the existence of different species of humans in the distant past.

How do we know about early humans?

Most of what we know about the lives of early humans comes from archaeology but in the past few years, scientists used the study of DNA to trace our origins.

Archaeologists study the past by looking at the things left behind by the people who lived before us. This includes remains of bones, tools, artwork, firepits, buildings, weapons, garbage and other objects (called artefacts) that were made, changed or used by people. The shape of the tool and the materials it was made from can give information about how people lived.

Homo naledi is an extinct species of humans that lived approximately 250,000 years ago. Bones from Homo naledi were first discovered in 2013 in the Rising Star Cave system in South Africa. This video tells the story of this amazing event.

The remains of more than six thousand early humans have been discovered. This video explains how our ideas about the evolution of early humans continues to be shaped by these discoveries.

Radiocarbon Dating
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.

Learning outcome 3.4- Differentiate between the genera and species of humans that have been identified.

TIMELINE OF HUMAN EVOLUTION

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.

All living things have a scientific name that is in two parts. The first part is the genus (plural - genera) and the second part indicates the species. Modern humans are in the genus Homo and the species sapiens. Homo sapiens means "wise man".

There are several species of humans that are now extinct. These include Homo habilis, Homo erectus, Homo neanderthalensis ("Neanderthal Man"), Homo nalini, and Homo floresiensis. The last Homo neanderthalensis lived about 30,000 years ago. There is some evidence that there were still Homo floresiensis in remote parts of Asia as recently as 12,000 years ago.

Scientists have also identified at least two now extinct genera of hominins that lived in Africa between 7 and 4 million years ago. The most important of these is Australopithicus.

Between 6 and 7 million years ago, the human lineage split from Chimpanzees. So far, about twenty hominin species have been discovered but only one species, Homo sapiens, remains..

The most famous early human is Lucy. She was an Australopithicus that lived in Africa about 3.2 million years ago.
Lucy's brain was much smaller than modern humans. However, she walked upright on two legs. She was probably a plant eater.

Learning outcome 3.5- Describe how early humans used fire and developed tools and other technology.

Some examples of technology used by Homo sapiens before they left Africa, about 60,000 years ago are:
* 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.

* Clothing
* 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.

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