2. It's hard to know when the Earth first formed,
because no rocks have survived from the
planet's earliest days. While scientists
disagree on the details, most researchers
think Earth formed by a series of collisions
that took place less than 100 million years
after the solar system coalesced. More than
10 impacts with other bodies added bulk to
our growing planet, according to most models
of Earth's formation.
By measuring the age of rocks on the moon,
and meteorites found on Earth, scientists
estimate the Earth consolidated by 4.54 billion
years ago. The young planet had established
an atmosphere and iron core-
5. The final collision in Earth's timeline was with Theia, a rocky
planetoid perhaps the size of Mars. This protoplanet sideswiped
Earth, leaving our planet mostly intact but destroying itself and
blowing away Earth's atmosphere. Theia's vaporized
debris condensed into Earth's moon.
6. Soon after the Earth coalesced in the early solar system, it was hit by
another planet, Theia. The collision formed the moon, but
researchers are still trying to piece together exactly what happened,
including what happened to Theia. For years, researchers have
thought that Theia might have smashed into Earth at an angle, strong
enough to obliterate Theia into little bits and create the moon.
7. Fact:
Scientists have found traces of Theia,
the planet that smashed into the Earth
to form the Moon, in lunar rocks
9. Earth’s rocky core forms first. Naturally, the heaviest materials, like iron and nickel
gravitate to the new planet’s center. Ultimately, these heavy elements will shape the
Earth’s core as we know it today. First, the solid central core, made primarily of iron.
Next, the liquid outer-core, made of nickel-iron alloy. Then, lighter materials gravitate
outward, eventually forming the Earth’s crust. Materials such as silicon, aluminum and
magnesium take shape to construct the mantel and crust we know today.
10. However, in our solar system’s early eras, comets were very abundant
throughout the entire system. Not to mention, these early comets often
collided with Earth. Actually, these impacts are thought to have caused our
life-saving watery surface. As the icy comets collided with a hot young
Earth, their melted contents slowly turned Earth’s fiery surface into our
oceanic home of today.
Today, comets are rather rare in the inner solar system. In fact,
comets only occur once every several decades, or more!
11.
12.
13.
14. Hadean Eon and the beginning of the Archaean Eon, about 3.8
billion years ago, Earth was still about three times as hot as it is today,
but it was no longer hot enough to boil water. Most of the Earth was
covered with oceans, and Earth's atmosphere was mainly carbon
dioxide with very little oxygen in it. Just a little bit of land was forming
as volcanoes began to poke out of the water. Most of the rocks
were igneous or metamorphic like granite or quartz. But the
earliest sedimentary rocks like sandstone also formed, mainly in the
oceans, during this time.
15.
16.
17. Also during this time, the Earth's crust
cooled enough that rocks and continental
plates began to form. It was early in the
Archean that life first appeared on Earth.
Our oldest fossils date to roughly 3.5
billion years ago, and consist of bacteria
microfossils.
About this time - around the beginning of the Archaean Eon, about
3.8 billion years ago - the earliest living cells formed on Earth. These
cells all lived in the oceans, which were probably much warmer and
more acidic than they are now. By about 3.5 billion years ago, these
early cells had evolved into simple prokaryote cells. For the rest of
the Archaean Eon, there were only prokaryote cells on Earth (and the
vast majority of cells on Earth are still prokaryotes).
18.
19. OXYGEN BEGAN TO
ACCUMULATE IN THE EARTH
“You cannot evolve animals like us without
having a significant amount of oxygen,” says
geochemist Dick Holland of Harvard University.
“Without the Great Oxidation Event [a dramatic
rise of oxygen in Earth’s atmosphere some 2.3
billion years ago], we would not be here. No
dinosaurs, no fish, no snakes – just a lot
of microorganisms.”
20. Most scientists believe that for half of Earth's 4.6-
billion-year history, the atmosphere contained
almost no oxygen. Cyanobacteria or blue-green
algae became the first microbes to
produce oxygen by photosynthesis, perhaps as
long ago as 3.5 billion years ago and certainly by
2.7 billion years ago.
Oxygen has not always been as abundant as it is today.
Most scientists believe that for half of Earth’s 4.6-
billion-year history, the atmosphere contained almost
no oxygen.
Cyanobacteria or blue-green algae became the first
microbes to produce oxygen by photosynthesis,
perhaps as long ago as 3.5 billion years ago and
certainly by 2.7 billion years ago. But, mysteriously,
there was a long lag time – hundreds of millions of
21. When did animals first appear?
Between 620 and 550 million years ago (during the Vendian
Period) relatively large, complex, soft-bodied multicellular
animals appear in the fossil record for the first time.
22.
23. Like the plants, animals evolved in the sea. And that
is where they remained for at least 600 million years. This
is because, in the absence of a protective ozone layer, the
land was bathed in lethal levels of UV radiation.
Once photosynthesis had raised atmospheric oxygen
levels high enough, the ozone layer formed, meaning that
it was then possible for living things to venture onto the
land.
25. Dinosaurs evolved from
other reptiles (socket-
toothed archosaurs )
during the Triassic
period, over 230 million
years ago.
26. Dinosaurs evolved soon after the Permian extinction, which was
the biggest mass extinction that ever occured on Earth. During
this time (the Triassic period), the mammals also evolved.
Dinosaurs lived between 230 and 65 million years ago, in a time
known as the Mesozoic Era. This was many millions of years
before the first modern humans, Homo sapiens, appeared.
Scientists divide the Mesozoic Era into three periods: the Triassic,
Jurassic and Cretaceous.
27. The last dinosaurs died approximately 65 million years ago (at the
end of the Cretaceous Period), after living on Earth for about 165 million
years. Although the cause of their extinction is still a mystery, climatic
change, diseases, changing plant communities, and geologic events could all
have played a role. Lately, dinosaur extinction theories have been the subject
of much debate and controversy.
BYE~BYE DINASAURS
