Category The Earth, Earth Science, Planet Earth

WHY DID IT TAKE SO LONG FOR LIFE TO APPEAR?

Earth’s surface was probably molten for many millions of years after its formation. Life did not exist for the first 400-800 million years, and first began in water after the forming of the oceans.

Life seems to have started on Earth almost as soon as the surface cooled off enough to make it possible. However, complex animal life—everything from insects to fish to humans – took a lot longer to show up. Given that modern animals are a phenomenally diverse group that evolved relatively quickly, why were they so slow to get going?

The answer may be that animals are greedy: they need a lot of oxygen to grow big and complicated. Early Earth didn’t have much oxygen, but microbes changed the chemical content of the atmosphere over time from something alien and poisonous to us into the breathable air we have today. A new paper showed that the oxygen level as recently as 800 million years ago was only a tiny fraction of today’s – far too low to support oxygen-breathers like our ancestors and their relatives.

Life on Earth has always belonged mainly to microorganisms. Clouds are full of microbes; they have been found in deep mines and on the ocean floor. They outnumber and may even outweigh all other forms of life. If all animals vanished, most bacteria would still live on, but if all bacteria disappeared, we would die quickly.

The history of life on Earth reflects this as well. The first single-celled organisms appeared about 3.8 billion years ago, while the first known multi-cellular organisms evolved 2.1 billion years ago. However, these were “primitive” in our human-centric eyes: they didn’t have specialized organs for breathing or eating, much less brains for the wasteful activity we call “thinking”.

Then in the Cambrian era, around 570 million years ago, recognizably complex animal life evolved, including vertebrate ancestors. This change was relatively rapid in evolutionary terms, and a lot of diverse critters came out of it. Thus, something significant must have changed between 2.1 billion years and 570 million years to let animals diversify and complexity.

To explain this great change, scientists consider several possible explanations. One environmental (as opposed to genetic) idea: animals breathe in oxygen, so there needs to be enough oxygen in the air and water. Corals, sponges, and the like require less oxygen than crabs or fish, so oxygen levels limit what sorts of animals can evolve in a particular environment.

Credit: Daily Beast

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WHAT IS EARTH MADE OF?

The structure of Earth can be divided into three parts: the crust, the mantle and the core. Made up from mainly oxygen and silicon, the crust is the outermost layer. It is the familiar landscape on which we live: rocks, soil and seabed. Beneath the crust is the mantle, a layer almost 3000 km deep. It is made of metal silicates, sulphides and oxides. This layer is so hot that the rock often flows like sticky road tar – only very, very slowly. Below the mantle is a core of metal, mostly iron, sulphur and nickel. The outer portion of the core is so very hot that the metal is always molten. The Earth’s magnetic field is created here. Earth’s inner core is even hotter – estimated to be around 6000 °C – but the metal is solid because pressure within the inner core is extreme, so the metal cannot melt.

1: The Core

The composition of the Earth begins with the inner parts of the planet. The Earth’s core is the densest part of the planet. It is made up of iron and nickel, and the core is so hot that is heats the rest of the planet around it. The core has chosen how the planet will be heated, and the core of the planet determines the equilibrium of the planet itself.

2: The Magma

The magma underneath the Earth’s surface spins around the world as it keeps the crust warm. The warmth of the magma can be felt in certain parts of the world where the ground is very close to the magma. The magma can be found rising out of the surface of the Earth at volcanoes and underwater cracks in the crust. The magma is the lifeblood of the Earth even though it is quite a scary thing to encounter today.

3: The Crust

The crust of the Earth is the ground that everyone walks on today. The crust is much thinner than the other components of the Earth, but it manages to support all the life on the planet. The Earth’s surface is covered with the crust completely, but much of the Earth’s surface is covered in water. Citizens of the Earth may never explore the floor of the sea, but that area is still a part of the Earth’s crust.

4: Magnetism

The magnetism of the Earth that helps it stay attached to the sun in orbit comes directly from the core. The core’s construction keeps the magnetism of the Earth going in ways that scientists do not understand completely. The magnetism created by the core also helps the Earth create a gravitational field that keeps everyone on the planet.

Credit: AES

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What are Twisters?

A thick, dark cloud forms in the sky. Warm air from near the earth rises rapidly towards the cloud. At the bottom of the cloud, the air starts spinning. This wind spins and twists and drops down into the shape of a long tube, or funnel. This wind is called a tornado, or twister.

The funnel may touch the earth’s surface. When a tornado touches ground, it can be dangerous. It can pick up heavy machinery and toss it far. The winds of a tornado rip roofs from houses and uproot large trees.

Tornadoes can happen in many parts of the world. But most tornadoes happen over the central U.S.A. People have recorded whirlwinds about 480 kilometres per hour there.

A tornado is a whirling wind that reaches down from the clouds and touches the ground. But dust devils and sand pillars are whirling winds that go from the ground up into the sky. They are much smaller than a tornado.

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What surrounds the Earth?

 

 

Long ago, people believed the sky was a roof that stretched over the earth. Today, we know that a thick layer of air surrounds the earth like the skin on an orange. But unlike an orange skin, the air moves around the earth, and it reaches far above the earth’s surface. This moving cover of air is a mixture of gases called the earth’s atmosphere.

Air covers the earth everywhere. The pull of gravity holds it there. Near the earth, the air is thick, or heavy. Further away from the earth, the air becomes thinner. Furthest away from the earth’s surface, the air thins and disappears altogether. Where this happens is where space begins!

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Who studies the waters?

Many scientists study the ocean, looking into the secrets of the sea. They study how the ocean moves and how it affects the atmosphere. They study the living things in the sea and the shape of the ocean floor.

Scientists who study the ocean are called oceanographers. Sometimes they work aboard ships. Some wear diving suits and air tanks to explore underwater. Others use small submarines. They use underwater cameras to take pictures of the ocean’s floor and the plants and animals that live in the ocean.

Sometimes they use robots to bring up samples of the mud and sand for study. Some scientists study the direction and strength of waves, tides, and currents.

Oceanographers called marine biologists study the plants, fish, and animals that live in the ocean, lakes, and rivers. They keep track of their health and the way they grow.

Oceanographers called seismologists study earthquakes that happen on the ocean floor. One cause of earthquakes is volcano eruptions, so seismologists often keep track of volcanic activity.

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What is underground water called?

Water from Underground

Not all of the earth’s water is in lakes, ponds, rivers, and oceans. A lot of it is beneath your feet – down in the ground.

Rain falls. Snow melts. Much of the water seeps into the ground. It passes through holes and cracks in the soil until it reaches solid rock. The water can’t trickle any further down, so it spreads out, filling every nook and cranny underground.

The top of this underground water is called the water table. When there is a lot of rain, the water soon fills all the open spaces underground. Then the water table gets higher.

In some places, the water table comes all the way to the top of the ground.

Then, water bubbles out and makes a natural fountain called a spring. Sometimes a spring is the start of a river.

Underground water is usually cool and clean and good to drink. People often dig wells to get this water. There is some underground water almost everywhere in the world – even in deserts. But in a desert, the water is often very, very far down underground.

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