Early life on Earth was very different from today:

• Atmosphere The atmosphere had almost no oxygen, and the sun’s harmful rays struck the Earth’s surface. 
• Life It took almost a billion years for Earth to become favorable for life. 
• Solar system Astronomers believe the first few million years in the solar system were unfriendly. 
• Universe The universe was opaque for nearly 400,000 years, so there are no direct observations of what happened during that time. Here are some other differences between early life and today:
  • Microbes: Microbes began living inside other microbes, functioning as organelles for them. 
  • DNA: DNA became packaged in nuclei for the first time. 
  • Organic molecules: Astronomers have detected organic molecules and amino acids scattered throughout space

All modern life shares a robust, hardy, efficient system of intertwined chemicals that propagate themselves. This system must have emerged from a simpler, less efficient, more delicate one. But what was that system, and why did it appear on, of all places, planet Earth

The early Earth was very different from our Earth today. The early Earth experienced frequent impacts from asteroids and meteorites and had much more frequent volcanic eruptions. There was no life on Earth for the first billion years because the atmosphere was not suitable for life.

Early life on Earth was very different from today. It took the Earth almost a billion years to become habitable. The atmosphere had almost no oxygen, and the sun’s harmful rays struck the Earth’s surface. 

Astronomers believe that the first few million years in the solar system were unfriendly. Even after the protoplanetary disk around the Sun evaporated, fragments and debris still littered the orbital lanes. 

Astronomers have detected organic molecules and amino acids scattered throughout space. This suggests that our planet was born from the maelstrom that surrounded our infant sun.

This question is about the central topic of abiogenesis, which explores how life’s complex chemical makeup emerged from simpler beginnings on Earth. 

The primordial system, which may have been delicate and less efficient, set the stage for the robust web of life we see today on Earth. This system must have emerged from a simpler, less efficient, more delicate one. 

The diversity and complexity of life on Earth is astonishing: 8 million or more living species — from algae to elephants — all evolved from a simple, single-celled common ancestor around 3.5 billion years ago. 

Some suggest that high CO2 concentrations (or a mixture of CO2 and CH4) in the early atmosphere were required to prevent Earth from freezing.

The early Earth was very different from today.  For the first billion years, the Earth’s surface was too hot for life to form.  The Earth experienced frequent asteroid and meteorite impacts and volcanic eruptions.  These impacts and eruptions created an atmosphere that contained nitrogen, carbon dioxide, hydrogen, and water vapor, but no free oxygen. Without oxygen, there was little that could live on Earth. 

Some evidence suggests that life may have emerged on Earth within the first 500 million years. Another study suggests that the Earth may have been habitable just over 200 million years after it formed. 

Early life forms were heterotrophs, meaning they couldn’t make their own food. It wasn’t until the evolution of autotrophs, organisms that make their own food, that oxygen began to slowly accumulate in the atmosphere

Earth is about 4.5 billion years old, and it took about 10–20 million years to form. Some evidence suggests that life may have emerged on Earth within the first 500 million years. Scientists think that by 4.3 billion years ago, Earth may have developed conditions suitable to support life. However, the oldest known fossils are only 3.7 billion years old. 

Earth is habitable because it’s the right distance from the Sun, it’s protected from harmful solar radiation by its magnetic field, it’s kept warm by an insulating atmosphere, and it has the right chemical ingredients for life, including water and carbon

Earth is at least 3.5 billion years old, according to the stromatolite record. Some computer models suggest life began as early as 4.5 billion years ago. 

The earliest life forms were prokaryotes, simple creatures that fed on carbon compounds in the early oceans. Other organisms evolved that used the Sun’s energy to generate their own energy. 

Some scientists think that life landed on Earth from somewhere else. A theory called panspermia says that life did not originate on Earth at all

The earliest evidence of life on land is fossilized microorganisms preserved in rocks from South Africa, which date back 3.2 billion years

However, the conventional view is that the first terrestrial life migrated out of the water around 430 million years ago. This period is known as the “Cambrian Explosion of Life”, when favorable conditions allowed life to branch out into most of the major forms in existence today. 

The earliest known land animal is Pneumodesmus newmani, a species of millipede that lived 428 million years ago. A single fossil specimen was discovered in 2004, in a layer of sandstone near Stonehaven, in Aberdeenshire, Scotland.

Some say that complex life first appeared on Earth 2.33 billion years ago, which is 800 million years earlier than the earliest fossil evidence. Others say that complex life began more than 1.5 billion years ago

The first complex life on Earth may have been strange, immobile organisms made of tubes that appeared 579 million years ago. These organisms thrived on the seafloor for 37 million years before disappearing. 

The first large multicellular organisms were the Ediacarans, which appeared about 700 million years ago. They lived in the ocean and disappeared around the time of the Cambrian explosion, when most familiar animal forms first evolved. 

One hypothesis suggests that all complex life forms originated when archaea and bacteria merged to form a hybrid organism.

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