4.2-3.9 billion years ago
Late Heavy Bombardment
A resonance between Jupiter and Saturn pushes Neptune to leave Uranus' orbit, and they both migrate into the outer solar system, producing a catastrophic disruption in the Kuiper Belt and sparking the late-heavy bombardment. A disproportionately high number of asteroids crashed with the inner Solar System's early terrestrial planets. Have you ever notice the craters on moon most of them were formed during this period.
Earliest Fossil Evidence of Life
Bacteria produce a protective organic substance known as exopolysaccharides while growing in stressful atmospheric conditions, which binds all the bacteria together to form a large slimy mat known as "biofilms." The capability of forming colonies gave them an opportunity to come close to one another and form protective rock-like structures capable of photosynthesis during the Archean aeon period. These specialized structures are known as "Stromatolites." These colonies allow them to share food and growth materials during times of difficulty or in a harsh environment.
Photosynthesis and The Great Oxidation Event
Once evolution begins, larger and more complicated cells, such as those that harvest the sun's energy. Photosynthesis produces oxygen, which progressively alters the atmosphere to the one we know today. The first oxygenic (oxygen-producing) cells were most likely blue-green algae (cyanobacteria), which arose between two and three billion years ago. Cyanophytes are prokaryotic cells, which means they lack separate membrane-enclosed subcellular components (organelles). These microscopic organisms are thought to have considerably boosted the oxygen level of the atmosphere, allowing aerobic (oxygen-using) life to flourish. This caused a quick and substantial increase in oxygen levels, making the environment less suitable for other microorganisms that couldn't withstand oxygen.
Cambrian Explosion: Appearance of Major Animal Groups
This was the period of rapid diversification and proliferation of life on Earth that occurred around 541 million years ago during the Cambrian period. During this time, there was an unprecedented increase in the number and diversity of fossilized organisms, including the first appearance of most major animal phyla. This sudden burst of evolutionary activity is thought to have been triggered by a combination of environmental factors, such as changes in sea level, temperature, and ocean chemistry, as well as the emergence of new predatory and defensive adaptations. The Cambrian Explosion is considered one of the most significant events in the history of life on Earth, as it laid the foundation for the subsequent evolution of the animal kingdom.
Dinosaurs and Reptile-Like Mammals
Dinosaurs originated during the Triassic Period, which began around 252 million years ago and lasted for about 50 million years. The first dinosaurs evolved from a group of reptiles called archosaurs, which had been present on Earth for millions of years prior. They first appeared in what is now South America but quickly spread to other parts of the world as the supercontinent Pangaea began to break apart.
Almost around same time, mammals also originated. The first mammals were small, nocturnal animals that lived alongside the dinosaurs. They evolved from a group of mammal-like reptiles known as therapsids, which had some characteristics of both reptiles and mammals.
Asteroid Impact and Extinction of Dinosaurs
The leading theory for their extinction is an asteroid impact, which caused a global catastrophe. The asteroid, estimated to be about 10-15 kilometers in diameter, struck the Earth with an enormous amount of force, releasing energy equivalent to billions of atomic bombs. The impact created a massive dust cloud that blocked out sunlight and caused a "nuclear winter" effect, causing the extinction of many forms of life, including the dinosaurs.
The extinction of the dinosaurs around 65 million years ago cleared the way for mammals to become the dominant land animals, and they continue to thrive today in a wide variety of environments.
The last common ancestor of humans and chimps.
The last common ancestor of chimpanzees and humans is believed to have existed around 6-7 million years ago. This ancestor is thought to have been a primate species that lived in Africa and was the common ancestor of both chimpanzees and humans. It is believed to have been a small, arboreal mammal with a similar body shape and brain size to modern chimpanzees. The exact identity of this ancestor is still unknown, but several extinct primate species, such as Sahelanthropus, Orrorin, and Ardipithecus, have been proposed as potential candidates.