The Earth we live on actually has a "dark history"?

Since the advent of satellites, people have known for the first time that the Earth is a blue and green planet when viewed from space - the blue is the ocean and the green is the vegetation on land. Since then, whenever people think of the Earth, they will first think of this classic image.

But in fact, the image of the Earth is not eternal. In the long period of more than 4 billion years before plants landed on the Earth, the appearance of the Earth changed no less than 10 times, just like the face-changing master in Sichuan Opera.

4.55 billion years ago

At this time, the Earth was just born. Simply put, countless asteroids with diameters of several kilometers collided with each other and gathered to grow. In the collision, kinetic energy was converted into heat energy, causing the originally rocky asteroids to melt into magma. At the same time, the radioactive elements carried by the asteroids began to sink and gather into the core of the Earth due to the melting of the asteroids, providing heat to the Earth in the form of radioactive decay.

At this time, the entire earth was a magma ball, so there was no distinction between land and sea. The earth at that time might have looked like this↓

The Earth was formed about 4.55 billion years ago. The impact of countless asteroids turned the Earth into a red magma ball. The ring in the picture was caused by the impact.

Image credit: flickr/Kevin Gill

4.5 billion years ago

About 4.5 billion years ago, the Earth began to cool down soon after it was formed. This is easy to understand. A cup of hot water will become room temperature water when placed at room temperature. The hot Earth will naturally cool down in the universe with an average temperature of -270℃. The bright magma cooled and turned into dark basaltic rocks, which covered the surface and turned the Earth black.

Of course, this process happens gradually. First, a small black spot appears on the red background, then the black spot grows larger, the red retreats, and finally the black almost covers the entire earth. Eventually, the earth as a whole becomes a black ball.

As the Earth gradually cools down, more and more black will appear, and eventually it will become a black Earth.

Image source: wikipedia/Jack Madden

At this time, there is still no distinction between land and sea in the general sense, but if you call the magma sea a sea, then the land on Earth might be like this↓

An imaginary picture of the Earth 4.5 billion years ago. Image source: NASA

During this period, the "land" on Earth was made entirely of black basalt, the sky was made of lead-gray silicate clouds with temperatures reaching hundreds or even thousands of degrees Celsius, and the "ocean" was red flowing magma.

About 4.4 billion years ago

As the Earth cooled, the surface finally solidified, and the originally hot silicate clouds cooled and fell to the surface in the form of silicate rain (the silicate clouds here can be simply understood as the products of melting and evaporation of various rocks; silicate rain can be simply understood as molten sand. If you still can't imagine it, go search for pictures of glass blowing, it's probably the same effect).

Then, as the temperature continues to drop, the water vapor in the clouds cools and condenses into rain.

Most of this water vapor comes from magma. In fact, there is also water in the composition of rocks. They are stored in rocks in the form of water molecules, hydrogen and hydroxide ions. When the rocks melt, they are mixed into the magma and eventually form free water molecules due to chemical reactions. As the magma is exposed to the surface, the water molecules evaporate into the atmosphere in the form of steam. This is the source of most of the water on Earth.

At this time, the entire earth may be surrounded by oceans, with a large number of volcanoes dotted in the oceans. These volcanoes either formed small volcanic islands above the water or formed submarine volcanoes underwater. In short, the three-layer structure of the earth's crust, mantle, and core had not yet been formed, so there was no plate activity or long mountains.

The Earth at that time might have looked like this, completely covered by sea water, with small volcanic islands scattered in the ocean. Image source: Wikipedia

If you look closely at the island, you may also find a large number of basalt columns, which may form the following scenery:

Basalt columns. Image source: Wikipedia

There are many such landscapes on the earth now, such as the famous Giant's Causeway, etc. In China, there are also such stone pillar landscapes everywhere, and the most famous one may be the Binhai Volcano National Geopark in Zhangzhou, Fujian.

About 4 billion years ago

The Earth may have formed a sphere structure at this time, and plate movement may have begun (but many scientists believe that this is not the case, and this issue is very controversial). Under the influence of plate movement, the small scattered land blocks originally formed on the Earth began to collide with each other, and the land changed from islands and small land blocks to large land, and mountains began to appear on the land.

In addition, continuous volcanic activity has also caused the area of ​​volcanic islands to begin to expand, and even connect into one, resulting in large and small land masses appearing on the earth.

But at this time, large-scale asteroid collisions began to occur in the solar system, and countless asteroids continuously hit the major rocky planets in the inner solar system. Scientists called this event the Late Heavy Bombardment.

During the period of heavy bombardment, although there was land on Earth, the Earth might have looked like a "pockmarked face".

Image credit: NASA

At this time, the Earth may have many meteorite craters, similar to the Moon, Mars, and Venus. The surface was barren and dry, and its macroscopic landscape was dominated by meteorite craters. Among them, large meteorite craters were sunken in the center, and the surrounding craters were raised to form craters.

A huge lake may have formed in the middle of the crater, and a river flowing downwards may have formed on the crater. But the land at this time is still extremely barren, with no signs of life.

A lake in the middle of a crater. Image credit: NASA

At the same time, due to the ups and downs of the surface, rivers appeared. As the rivers flowed, they began to wash away the surrounding basalt land, grinding the basalt and carrying it away.
In some long rivers, due to the long-distance transportation of rivers, many dark-colored minerals in basalt are eroded and disappear, leaving only light-colored minerals. Therefore, in addition to dark-colored igneous rocks, light-colored sedimentary rocks also begin to appear on the surface at this time.

Modern rivers flowing through basalt columns may have been seen everywhere on Earth 4 billion years ago, but without exception, there was no life.

Image source: wikicommons

3.8-3.5 billion years ago

After long-term river scouring and sedimentation, the surface at this time may have begun to be covered by sedimentary rocks. The original large-scale dark tones have faded, and the overall surface at this time may be light-colored - such as light yellow.

There are still small peaks (or mountain ranges) on the land, rivers running between the mountains, and the craters on the land are still densely packed.

Scientists imagine what it would be like if there was water on Mars. Image credit: NASA

The biggest attraction at this time is the earliest organisms.

However, the organisms at this time were only some marine microorganisms, some of which lived in the ocean and some of which gathered on the coast in the form of microbial algae mats (the small lumps on the seashore on the right in the picture below). The fossils formed by these algae mats are called stromatolites, and stromatolites exist all over the world today.

A seaside scene might look like the picture below, but the color might be similar to the yellow hue in the first picture.

An imaginary picture of the seaside scenery at this time. Image source: wikipedia

2.5 billion years ago

At this time, the earliest continent appeared, named Kenorland (controversial), and plate movement was confirmed to have started, and large-scale mountains began to form on land.
In addition, early photosynthetic organisms appeared and oxygen began to appear in the atmosphere. This oxygen quickly oxidized the iron on the land, giving the land an overall red hue.

Whether the Nolan Continent exists and what its form is is still controversial. Image source: Wikipedia

This is scientists' imagination of what Mars looked like more than 3 billion years ago. The Earth was probably similar to this at that time, or even a little redder, because the Earth had more oxygen, which could oxidize iron more completely.

Image credit: ESO

If we observe deeply on land, we will find that there should have been mountains, rivers, deltas and other landforms on land at that time, but the land was barren and had no vegetation cover.

The details of the Earth's geomorphology at that time should be similar to those of Mars today, and we can find the shadow of the Earth at that time on Mars.

This image is a NASA artist's imagination of Mars with water. From the perspective of space, the Earth at that time might be similar to this, but the Earth might be a little more red. Image source: NASA

At that time, there was also a Grand Canyon on Earth, a landscape shaped by huge rivers. Image source: NASA

Scientists have reconstructed the rivers and deltas on Mars. There is also an obvious meteorite crater on the delta. At that time, the land on Earth was also full of meteorite craters. Image source: NASA

Waterless inland mountains. Image credit: NASA

The desert at the foot of the mountain. Image source: NASA

About 2.4 billion years ago

Due to the massive growth of plankton in the ocean, plants absorbed a huge amount of carbon dioxide through photosynthesis, causing the earth to cool down. At this time, the earth entered a great ice age, which some scientists call the first snowball earth event. At this time, both land and ocean were covered with ice and snow, so the earth was like a snowball, and the land was also white.

The Earth is covered in ice and snow. Image credit: MIKKEL JUUL JENSEN/SPL/COSMOS)

Glacial lakes and rivers on land at the time may have looked similar. Image credit: ESA-A.Gers

The mountains on land were also covered in ice and snow, similar to Antarctica today. Image credit: Anne Fröhlich

Of course, it's not completely devoid of life. In some open seas, you can still see many algae living together. They may dye the entire ocean into blue-green strips, which may look like this↓

The ocean is dyed into blue-green stripes. Image credit: NASA

About 2 billion years ago

As volcanoes continued to erupt, carbon dioxide accumulated in the atmosphere again, the earth returned to warmth, the ice age ended, and the earth returned to its previous appearance - huge blue oceans dotted with red continents.

An image of the Earth after the Ice Age. Image credit: NASA

About 700 million years ago

As the climate cools, the earth turns into a snowball again, refer to the previous section.

About 500 million years ago

By this time, plants had already adapted to freshwater environments, and the earliest plants may have even begun to land. However, it is certain that some blue-green algae landed on land before plants, and they coexisted with certain fungi to form lichens, which covered the rocks on the coasts of rivers and lakes and were colorful.

Some primitive phytoplankton may have adapted to the freshwater environment and began to reproduce in inland freshwater rivers and lakes. At the same time, some lichens may have also landed on land. The green spots on the waterside in the picture may be these organisms. Image source: NASA

Lichens on modern rocks. Image source: Wikipedia

About 450 million years ago

Plants landed...and the earth gradually became what we are familiar with.

Produced by | Science Popularization China

Author: Earth's Gravity

Producer｜China Science Expo

Submitted by: Computer Information Network Center, Chinese Academy of Sciences