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.
4.
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
15.
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 .
26.
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 .
