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- 1. When Did Humans First Appear On Earth?
- 2. • Humans first appeared on Earth at least 315,000 years ago. This figure is based on fossil remains found in Jebel Irhoud, Morocco – the earliest-known remains of modern humans. The exact time humans first appeared is difficult to judge because species don’t come into being overnight. Rather, they change and evolve slowly from ancestral species. our species will therefore have appeared some time before this. DNA evidence from human chromosomes indicates that humans (scientific name: Homo sapiens) may have first appeared more than half a million years ago.
- 3. • This may sound like a long time, but the ancestral species that gave rise to the early humans found in Morocco all arose in Africa, and their history stretches back even further, to some six million years in the past. The evolution of these ancestral species is characterized, in particular, by the development of progressively larger and more complex brains. The very oldest human fossils come from Africa; this includes those from Jebel Irhoud, along with others from Ethiopia in East Africa (dated at 196,000 and 160,000 years ago). This has led archaeologists to conclude that our species evolved in Africa.
- 5. How did modern humans spread around the world? • The short answer to this question is that they walked, mostly. About 70,000 years ago a single, small group of anatomically modern Homo sapiens left East Africa and began to spread eastwards. Along the way they settled, and their populations increased. Further dispersal followed, and the people slowly moved along the southern coast of the Arabian Peninsula, Asia and the Indonesian Islands. Populations reached Australia by 50,000 years ago.
- 6. • In addition, descendants from the original group also migrated northwards to Europe, arriving some 40,000 years ago. Other descendants populated central Asia and lastly, some 20,000 years ago, the first modern humans arrived in the Americas from Asia. It is thought that some of these early Americans arrived by boat, while others came on foot. This means that all humans alive today descended from African ancestors.
- 7. Extinction • An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms Scientists estimate that at least 99.9 percent of all species of plants and animals that ever lived are now extinct. So the demise of dinosaurs from 65 million years ago wouldn't be especially noteworthy—except for the fact that around 50 percent of all plants and animals alive at the same time also died out in what scientists call a mass extinction.
- 8. • when at least half of all species die out in a relatively short time—have occurred only a handful of times over the course of our planet's history. The largest mass extinction event happened around 250 million years ago, when at least half of all species die out in a relatively short time—have occurred only a handful of times over the course of our planet's history. The largest mass extinction event happened around 250 million years ago.
- 9. Silurian- Ordovician Extinction: 440 million years ago: Small marine organisms died out . Devonian Extinction:365 million years ago;Many tropical marine species went extinct. Permian- triassic Extinction: 250 million years ago :including many vertebrates . Triassic- jurassic Extinction:210 million years ago:the extinction of other vertebrate species on land allowed dinosaurs to flourish. Cretaceous-tertiary Extinction:65 Million Years Ago:dinosaurs, Marine reptiles and giant crocodiles
- 10. Today extinction Earth is currently a biodiversity crisis. Recent estimates suggest that extinction threatens up to a million species of plants and animals, in large part because of human activities such as deforestation, hunting, and overfishing. Humans’ burning of fossil fuels has let us chemically imitate large igneous provinces, through the injection of billions of tons of carbon dioxide and other gases into Earth’s atmosphere each year. Earth’s climate is rapidly changing as a result .
- 11. Geographic distripution • What is biogeography? The study of the geographical distribution of organisms, provides information about how and when species may have evolved.
- 12. • How it supports evolution? Supports this feature of the theory of evolution... for a new species to arise, a group of individuals must become isolated from the rest. They look the same but live in different areas. It shows that island species have a lot of similarities to animals on the closed mainland. It shows how species have adapted for the climate that they live in.
- 13. The fossil record • The fossil record provides snapshots of the past which, when assembled, illustrate a panorama of evolutionary change over the past 3.5 billion years. clearly shows that life is very old and has changed over time through evolution. Fossils give us a useful insight into the history of life on Earth. They can teach us where life and humans came from, show us how the Earth and our environment have changed through geological time, and how continents, now widely separated,were once connected .
- 14. • Fossils have been found on every continent of Earth and in every geologic age and are found almost exclusively in sedimentary rocks An example of the fossil record is archaeopteryx, a flying dinosaur that shows the transition from dinosaurs to birds. Some of the preserved specimens show evidence of feathers and wings, characteristics found in modern birds
- 16. Time line of evolution • Before 4.5 billion years: Planet Earth appeared and was unsuitable for life as we know it today several hundred degrees above or below zero, deadly gases, and most important of all, the planet was devoid of water condense from steam to become liquid. The meteorites and comets that were falling on Earth in abundance at that time helped bring more gases and form oceans .
- 17. • Before 3.5 billion years: water the first elements of life assembled despite heat, ammonia and methane, from organic compounds to basic and primitive protein structures to the first types of cells called prokaryotes. _Since that time, these cells began to accumulate in the form of algae, the first of which was blue algae - cyanobacteria - which were formations of organic life and minerals that were capable of photosynthesis ( converting solar light energy (electromagnetic) into chemical energy stored in glucose bonds) .
- 18. • Before 3 billion years: Most of these bacteria spread to contribute to the reduction of carbon dioxide from the atmosphere and the secretion of large amounts of oxygen (the beginning of photosynthesis), which in turn began and formed an atmosphere ( ozone ) capable of absorbing ultraviolet rays and thus allowing life to develop more and more.
- 19. • Before 800 million years: Since that ,eukaryotic cells began to appear and then uniting to form a tissue and each of them has its own role (a division specialized in reproduction, another in movement, and another in communication...) because nature prefers Symmetry These tissues began to take appropriate forms, take best form for them to be cabable of resistance and suitable for the environment in which they live (water, rocks). The largest can be seen .
- 20. • 500 million years ago: The first types of animals were marine, and invertebrates : sponges, jellyfish, fungi, crustaceans, primitive worms, mollusks, the first type of worms that did not have a palate (jaw) and they entered the bodies of others to live Inside it sucks blood and food directly.
- 21. • 480 million years: These species evolution to appear vertebrates (the appearance of the skeleton) and then the first fish. 450 million years: At this time, then fish appeared, and all forms of life, plant or animal, were marine, at that time the continents (land) were moving.
- 22. • 400 million years: marine organisms lived in an ocean between three pieces of land almost on the equator, and where the land began to move closer to each other there due to geological factors, and thus the creatures had to coexist with each other around that spot of the earth and always In the waters, in a highly competitive environment, large and powerful creatures will find more prey, and the small and weak have no choice but to evolve. Starting from this period, the first creatures with a palate (jaw) appeared.
- 23. • 380 million years: Water began to form of the continent and mountains appeared, and the rain, snow and ice, and thus to form rivers and fresh water . Thus, the land became a fertile place for the growth of various organisms from plants to algae, and thus fish began to evolve to escape from large prey in the water towards the land through rivers. _These organisms: tree roots, algae and fungi consume more oxygen than water provides, and thus the lungs began to develop to be able to breathe outside of water and obtain oxygen directly from the air.
- 24. • Before 360 million years: This evolution in respiration means that fish have to stay close to the surface of the water, and if they stay for a long time in the water, they will sink, so they had to start to develop new ways to cross the land, and the appearance of the first amphibians is recorded . Before 300 million years: Reptiles began to appear
- 25. • Before 280 million years: The evolution of walking on land for animals to develop four feet with toes, in the beginning these feet helped the organism to walk in the water and when these feet became strong to become able to carry the weight of the animal comes out of the water to venture on land. Before 200 million years: Fingers evolved to become different from each other and became able to grasp things, which led to the emergence of the hand and the first major mammal species and humans .
- 27. Biochemical similarities between organisms • Evidence for common descent has come from the study of biochemical similarities between organisms. At the most basic level, all living organisms share: - the same genetic material (DNA). - the same, or highly similar, genetic codes. - the same basic process of gene expression (transcription and translation). - the same molecular building blocks, such as amino acids. This revealed that all living organisms are descended from a common ancestor. These features were inherited from the ancestor If we want to determine which organisms in a group are most closely related, we need to use different types of molecular features, such as the
- 28. • For example humans, caws, chickens and chimpanz ees all have a gene that encodes the hormone insulin, because this gene was already present in their last common ancestor. For example humans and chimpanzee insulin proteins are much more similar (about 96% identical) than human and chicken insulin proteins (about 64% identical) , reflecting that humans and chimpanzees are more closely related than humans and chickens.
- 29. • Another example for biochemical similarities between organisms, the metabolism of different organisms is based on the same complex biochemical compounds. The protein cytochrome c , essential for aerobic respiration, is one universal compound and this is evidence that all aerobic organisms probably descended from common ancestor. Certain blood proteins found in almost all organisms give additional evidence that these organisms descended from a common ancestor. But there are variations in the amino acid sequence of cytochrome c in different species.
- 30. • For example, the cytochrome c of monkeys and cows is more similar than the cytochrome c of monkeys and fish. Such similarities and differences suggest that monkeys and cows is more closely related than are monkeys and fish. This evidence implies that some species share a more recent common ancestor .
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