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Origin of Life on Earth: From Hadean to Cambrian Period

Origin of Life on Earth

Life on Earth: Earth is estimated to be about 4.5 billion years old, and for much of that history, it has been home to life in one form or another. Today, there are several theories about the evolution of life on Earth. The first of these is that life was created by a Supreme being or spiritual force. The second theory is that life began in another part of the Universe, and arrived on Earth by accident when a comet or meteor crashed.

Origin of Life on Earth

In the beginning, the Earth’s atmosphere was made up of only nitrogen, carbon dioxide, and some hydrogen. There was very little oxygen present, and it was produced by stromatolites- which are rocks formed by the growth of blue-green algae- strewn in the sea. Whatever oxygen was present was quickly absorbed by rocks and minerals. Gradually, however, excess oxygen began to accumulate in the atmosphere. This excess oxygen had a dramatic effect on the living cells. It triggered the evolution of a higher form of life. These were nucleus-containing eukaryotic cells. Thus, the simple blue-green algae that were the first form of life, became stepping stones to higher life forms, thanks to rising oxygen levels in the atmosphere.

Scientists say that life began around 3.5 billion years ago as a result of a complex sequence of chemical reactions that took place spontaneously in the Earth’s atmosphere. Molecules were formed as a result of these reactions. The molecules then interacted with one another, and this eventually led to the earliest forms of life. The first beings were probably bacteria that survived on naturally occurring food and did not breathe oxygen. The fossils of these oldest forms of life have been found in Australian rocks dating back 3.5 billion years.

Periods of Life on Earth

Hadean Period

The Hadean Period started when the Earth has formed about 4.5 billion years ago. During Hadean times, the Solar System was forming, probably within a large cloud of gas and dust around the sun. The sun was formed within such a cloud of gas and dust. The tendency of matter to clump together finally resulted in the formation of substantial bodies like the planets, and their moons. The oldest Earth rocks and Moon rocks we know about, both date to this time.

Water was brought to Earth by comets that crashed into the Earth. This water boiled into steam, because the Earth was still very hot, and formed a steam atmosphere around the Earth. As the Earth cooled down, about 4.3 billion years ago, the steam in the atmosphere also cooled down and fell as rain on the Earth, and that made the oceans. By 4.2 billion years ago, Earth had land and oceans.

Archaean Period

The Archaean Period lasted from 3800 to 2500 million years ago. The Earth was still about three times as hot as it is today, and most of its area was covered with oceans. The Earth’s atmosphere was mainly carbon dioxide, with very little oxygen in it. The land was beginning to form as volcanoes that emerged from the oceans.

The forming of the continents also began during this period, probably as lava flow under the ancient oceans. About this time, the earliest living cells formed on Earth. These cells all lived in the oceans. One type of bacteria present was the cyanobacteria or blue-green algae.

These bacteria appear to have had a very strong cell-wall, and the ability to form layers in the ancient sediments. The formations are called stromatolites. They can be found in Archaean rock formations of Western Australia. So to sum up, the Archaean Period was a time of continent- building, and the first stages of early life on earth can be traced back to this period.

Proterozoic Era

The Proterozoic Era was between 2.5 billion and 542 million years ago. One of the most important events of this era was the gathering of oxygen in the Earth’s atmosphere. Near the end of the Proterozoic Era, about 600 million years ago, creatures with more than one cell, like hydras, jellyfish, and sponges lived in the oceans.

About 550 million years ago, these creatures evolved into flatworms, then roundworms, and finally, into segmented worms. Thus, it was during this period that the first multi-cellular organisms came into existence. It was during the Proterozoic Era that fiery formation processes of the Hadean and the undersea continent-building of the Archaean were replaced by the process of plate tectonics. As a result, a single super-continent formed. Today, it is called Rodinia.

Vendian Period

The Vendian Period began about 650 million years ago and ended about 543 million years ago with the beginning of the Cambrian Period. The Vendian is when the earliest known animals evolved. These in-eluded soft-bodied multi-cellular animals, like sponges and worms.

During the Vendian, the continents had merged into a single supercontinent called Rod in it. In the 20th century, macroscopic fossils of soft-bodied animals, algae, and fossil bacteria have been found in rocks attributed to the Vendian Period in a few localities around the world. The Vendian is also known as the Ediacaran or as the Proterozoic.

Precambrian Period

The Precambrian Period spans a long period of the Earth’s history. It starts with the planet’s creation about 4.5 billion years ago and ends with the emergence of complex, multicelled life-forms almost four billion years later. It is extremely significant because it is: the earliest of the geologic agee; – which a remarked by different layers of sedimentary rock. Laid down over millions of years, these rock layers contain a permanent record of the Earth’s past, including the fossilized remains of plants and animals buried when the sediments were formed.

The Precambrian is divided into two parts- the Archaean time, and the Proterozoic Era. There may not have been many different forms of life on earth, but very important changes were taking place during the Precambrian. The Earth was formed, and its outer covering cooled and hardened into a crust. The hot molten insides of the Earth leaked out at weak places in the crust to form volcanoes.

The clouds formed by the volcanoes caused huge amounts of rain to fall, and the oceans were created. The first life formed. The oceans were like thick soup, and their chemistry made them the perfect place for life on earth to begin. The first one-celled organisms formed during the Precambrian Era. They had an important job to do. They helped make the air and water around the Earth full of oxygen.

Once there was plenty of oxygen, new life could form. This life would have many cells that would evolve into different kinds of animals. All of the important work of the Precambrian period made the Earth ready for what would come next.

Cambrian period

The Cambrian Period lasted for nearly 53 million years, from about 543 million years ago, until 490 million years ago. The continents were still forming but were mostly barren rocks. The land had no plant or animal life on it yet. During the Cambrian Period, there was an explosion of life forms. Most of these were in the water. Many animals with no backbones lived in the shallow seas. The most plentiful species during this period were trilobites. You can read more about the Cambrian Period in a separate post.


20 Mindboggling Fun Facts about Heart for Kids

Fun Facts about Heart

Fun Facts about Heart

The heart is the hollow muscular organ located behind the sternum and between the lungs; its rhythmic contractions move the blood through the body. In all humans, other mammals, and birds, the heart has 4 chambers while in fishes it is divided into two chambers.

Did you know that heart-related diseases or CVD account for 32% of all human deaths around the globe as of 2015? Isn’t that scary? Here is a list of 20 Amazing Fun Facts about Heart, check it out!

Fun Facts about Heart


#1 Xenographic transplants involve taking an organ from an animal and using it in a human being – a chimpanzee heart was transplanted into a man in Mississippi, the USA in 1964, but the patient died two hours later.

#2 Your right lung is larger than your left – this is because the left lung needs to make room for your heart. Did you know Your heart beats about 35 million times a year?

#3 The pressure created by your heart can squirt blood almost ten meters.

#4 The blue whale has the slowest heartbeat of any animal – it only beats four to eight times a minute.

#5 The heart is the only muscle that doesn’t take its signal from the nervous system – it has its own stimulator in the right atrium.

#6 The larvae of the pork tapeworm, hatched from eggs eaten in infected pork, can travel around the body and live in the brain, eyes, heart, or muscles.

#7 A giraffe has special valves in its arteries so that its blood can reach up to its head. Without them, it would need a heart as big as its whole body!

#8 About 70 milliliters (around 2.5 fluid ounces) of blood are spurted out of your heart with each beat.

#9 Your heart pumps around 182 million liters (48 million gallons) of blood in your lifetime – with an endless supply of blood, it could fill a swimming pool in less than a month!

#10 Nuttall’s poorwill is an American bird that hibernates in the winter, hiding in a crack in a rock. During this time, it uses only a thirtieth of the energy it uses in the summer and its heartbeat becomes so faint that it can’t be felt.


#11 When you sneeze, all your body functions stop – even your heart stops beating. A very long sneezing fit can cause a heart attack.

#12 Newts can re-grow body parts that are lost or damaged, including legs, eyes, and even hearts. Scientists who have studied how they do this think they might be able to persuade human bodies to do the same.


#13 In Vietnam, cobra hearts are a common snack. They can be eaten raw, even still beating, with a small glass of cobra blood or dropped into a glass of rice wine. The kidney is often included as an extra titbit.

#14 The Scottish dish haggis is made by cutting up the heart, lungs, liver, and small intestine of a calf or sheep and cooking it with suet, oatmeal, onions, and herbs in the animal’s stomach.

#15 During heart surgery in 1970, a patient with hemophilia (an inherited condition which stops the blood clotting) needed 1,080 liters of blood – nearly 15 baths full – as he kept bleeding.

#16 The poet Shelley drowned off the coast of Italy in 1822. His body was washed up, half-eaten by fish, and cremated on the beach by his friends. One of them cut his heart from the burnt body and gave it to Shelley’s wife who kept it all her life.

#17 The glass frog is lime green but has a completely transparent stomach. It’s possible to see the blood vessels, the heart, and even check whether it’s eaten recently or might like a snack.

Glass Frog

#18 People who killed themselves used to be buried at a crossroads with a stake through their heart. It was thought that they couldn’t go to heaven, and the cross-roads would confuse their ghost so that it couldn’t find the way home to haunt anyone.

#19 A robotic caterpillar controlled by a joystick can be inserted through a small hole in the chest, and crawl over a person’s heart to inject drugs or install implants to heal any damage. Is it nanotechnology?

#20 Apart from the heart, an Egyptian mummy doesn’t have any internal organs left inside the body. The others were removed and put into separate canopic jars that were buried with it. You can continue reading 10 More interesting facts about the Human Digestive System.

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Dinosaurs – Facts about the Ruling Reptiles & Their Types


Dinosaurs fossils were probably discovered by the ancient Chinese, Romans, and Greeks. However, no one really recognized them as belonging to an extinct animal. Much later in 1676, a huge thigh bone was found in England by Reverend Plot.

It was thought that the bone belonged to a ‘giant’ but was probably from a dinosaur. The first dinosaur to be described scientifically was Megalosaurus, named in 1824, by William Buckland.

The name ‘dinosaur’ which means ‘terrible lizard,’ was actually coined by Richard Owen. In 1838, William Parker Foulke found the first nearly complete dinosaur fossil remains in New Jersey, USA. Since Buckland’s original discovery in 1819, approximately 330 different dinosaur genera have been discovered thus far.

The Ruling Reptiles

The Jurassic Period started around 205 million years ago and is known as the time when dinosaurs, who were reptiles, ruled the Earth. Dinosaurs were now much larger, which clearly put them at the top of the food chain.

Some of the largest dinosaurs of the Jurassic age were the herbivore plant-eating sauropods. Thanks to the abundant plant life, massive herbivores such as the brachiosaurus, diplodocus, and apatosaurus had no shortage of food.

The fiercest among the carnivorous dinosaurs were extremely large theropods like the allosaurus and the ceratosaurus. The allosaurus was probably the top Jurassic predator of its time, and with the largest specimen coming in at a length of over 9 meters and its prey was most likely the large herbivores such as the sauropods.

Flying reptiles like the pterosaurs were still the dominant air species. It was the first feathered flying species, and clearly an evolutionary step towards the bird species.

Marine reptiles consisted mainly of the plesiosaurs, ichthyosaurs, large marine crocodiles, variations of modern-day sharks, as well as cephalopods which are relatives of today’s squid and octopus species.

Different Types of Dinosaurs

Types of Dinosaurs

There were many different kinds of dinosaurs. The smallest types were about the size of a chicken, and the largest was over 100 feet, or 30 meters long.

  • Some ate only meat and were known as ‘carnivores’.
  • Some ate only plants and were herbivores.
  • Others ate both plants and meats and were ‘omnivores’.

Herbivorous dinosaurs were usually larger in size and had longer necks than the others as they evolved to scare carnivorous dinosaurs who hunted them for food. They usually lived in herds and had short and blunt teeth for chewing on plants. They probably swallowed stones to aid them in their digestion.

Carnivorous dinosaurs were large in size, and they usually walked on their hind limbs. They had long and sharp teeth for killing their prey and ripping their flesh for food. Omnivorous dinosaurs were not as large as carnivorous dinosaurs. They usually walked on their hind limbs, but they did not have specific kinds of teeth as they consumed plants, animals, and even eggs.

They are also classified as being lizard-hipped or bird-hipped. Some common dinosaurs are the Acrocanthosaurus, tyrannosaurus rex, spinosaurus, brachiosaurus, and diplodocus. Till now, more than 700 different species of dinosaurs have been identified.

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Popular evolution theories before Charles Darwin

Lamarck - evolution theories

Early scientists were not interested in any theories of evolution or not even aware of such concepts. At first, they were even reluctant to accept the idea that some animals had become extinct. According to the Bible, even when a great flood covered the Earth, Noah had managed to save a male and female of all species to ensure that no animal would become extinct. When the first fossils of unknown animals were discovered, it was believed that these animals still existed in some unexplored regions of the Earth.

However, the discovery of fossils of giant animals like the mastodon shook this belief, as it was unlikely that there were unexplored regions large enough to hide such animals. French scientists were the first to accept that these giant animals might have roamed the Earth thousands of years ago, and become extinct due to a variety of causes. Slowly, this idea came to be accepted worldwide. Scientists began their work on evolution theories, and Lamarck was first among them. Later among all these evolution theories, Theory of Evolution by Charles Darwin became popular and most accepted to date by the scientific community.

Jean Baptiste Lamarck

Jean Baptiste Lamarck was a French scientist who developed a theory of evolution at the beginning of the 19th century. His theory involved two ideas. The first was the law of use and disuse, which stated that a characteristic which is used more and more by an organism becomes bigger and stronger, and one that is not used, eventually disappears. The second law was the law of inheritance of acquired characteristics. It stated that any feature of an organism that is improved through use is passed to its offspring.

However, Lamarck’s theory cannot account for all the observations made about life on Earth. For instance, his theory would predict that all organisms gradually become complex, and simple organisms disappear. But we know that this is not the case, and those simple organisms still exist. So today, Lamarck’s theory of evolution is largely ignored.

Jean Baptiste Lamarck believed that all bodies had ‘subtle fluids’. These were weightless fluids pervading all space and bodies. Two good examples of eighteenth-century subtle fluids were electricity and heat. Lamarck believed that subtle fluids were responsible for both movement and change.

For example, he pointed out that snails have poor vision because feelers on their head acted as their eyes. According to him, the ancestors of snails did not have feelers. They groped about with their heads to find their way around. This groping sent subtle fluids to the front of the head, and the constant presence of moving subtle fluids eventually brought about the development of feelers, and these feelers were passed from generation to generation.

Charles Willson Peale

Charles Willson Peale founded a museum in Philadelphia, Pennsylvania, in 1786. It contained a collection of natural history specimens, portraits of admirable historical figures, and human artifacts from various countries. His purpose was to show the place of human beings as part of the animal kingdom. His most famous display, however, was the mastodon skeleton he obtained in 1801.

Measuring 3.35 meters high at the shoulder, and 4.5 meters from chin to rump, it was huge and strange and confusing. Was it a man or beast, an elephant, or some unknown animal? The fossil had been discovered in swampy ground and had been excavated with great difficulty. Man or beast, this ‘monstrous creature’, as it was called, would soon become celebrated as the unknown species or the ‘incognitum’.

Georges Cuvier

For many years, scientists refused to accept that some animals had become extinct. When remains were found that were unlike anything living at the time, they argued that they were unusual examples of living creatures, or that animals known only from fossils must still survive in some unexplored part of the world.

It was only at the end of the 18th century that the great French paleontologist and anatomist Georges Cuvier was able to demonstrate convincingly that extinctions were real. Cuvier was convinced that plants and animals of all types were created for their particular roles and places in the world’s environment and that they were unchanging throughout their existence.

According to him, catastrophic events in the course of history had killed off all members of some species, and their fossils would no longer be seen in the rocks. Subsequently, his evolution theory suggests, the old species were replaced by new ones that repopulated Earth.

Cuvier had an almost uncanny ability to reconstruct animals from only fragments of fossil remains. With elegant studies of the anatomy of large mammals such as elephants, Cuvier showed that fossil mammoths differed from any such creatures presently living. His many examples of fossils telling the stories of animals that lived and then disappeared were taken as incontrovertible proof of extinctions.

Hugh Miller

Hugh Miller was a 19th-century geologist. He put forward the theory that there had been several successive creations, and that each had been destroyed by a catastrophe. According to him, the Bible dealt with only the last creation. Miller’s theory of evolution explained the presence of fossils as being the remains of animals from an earlier creation.

Louis Agassiz

Louis Agassiz was a Professor of Zoology and Geology. He did landmark work on glacier activity and extinct fishes. He encouraged learning through direct observation of nature. Agassiz put forward the theory of a new catastrophe the Ice Age.

He believed that a sudden intense Ice Age gripped the Earth for ages, and wiped out all the existing animals and plants. His concept of the Great Ice Age brought him much fame, as he was able to present evidence in the field, especially the scratched surfaces of bedrock where rocks in the moving ice had gouged out deep marks.

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