【PEP Edition】Junior High Biology — Grade 8, Volume 2: The Mystery of Life's Origins: Primitive Earth Environment

Welcome to4.6 billion years agoEarth. A barren world where we could not breathe. It was a time of extreme turmoil — rivers of lava flowed across the surface, and relentless meteor impacts scarred the land. By looking at the craters on the Moon, we can imagine the staggering landscape of early Earth.

₄, NH₃, H₂O, H₂, CO₂ (no O₂) Energy Sources: Lightning, High Heat, UV Radiation

Nature's "Laboratory" for the Evolution of Life

The composition of the primitive atmosphere was vastly different from today's. It consisted of water vapor, hydrogen, ammonia, methane, carbon dioxide, hydrogen sulfide, and other gases released by volcanic eruptions. The most crucial point:There was absolutely no free oxygen in the primitive atmosphere. This reducing environment was the prerequisite for chemical evolution.

Energy Trigger: Lightning in the sky, intense ultraviolet radiation, and the high temperatures generated by tectonic activity broke the chemical bonds of small inorganic molecules.
Primordial Ocean: As the surface cooled, rainfall gathered to form the primordial ocean. Small organic molecules accumulated here with the rainwater, creating the famous "primordial soup."

Key Takeaway

The primordial ocean was the cradle of life. Here, over vast stretches of time and driven by energy, non-living matter gradually made the leap from inorganic to organic compounds, and from simple organic molecules to complex primitive life forms.

QUESTION 1

According to the text, what is the key difference between the composition of Earth's primitive atmosphere and today's atmosphere?

The primitive atmosphere contained large amounts of oxygen and ozone.

The primitive atmosphere had absolutely no free oxygen, while today's atmosphere contains about 21% oxygen.

The primitive atmosphere had no carbon dioxide, while today's atmosphere has a very high level of it.

Their compositions are exactly the same, only the concentrations differ.

QUESTION 2

Determine whether the following statements are true or false: (1) The primitive atmosphere contained gases such as oxygen and carbon dioxide. (2) American scientist Miller's simulation experiment showed that organic compounds like proteins, which make up living organisms, could form on early Earth.

(1) True; (2) True

(1) False; (2) False

(1) False; (2) True

(1) True; (2) False

QUESTION 3

The ancient Chinese philosopher Laozi said, "All things under heaven are born of the existent; the existent is born of the non-existent." Does this align with the modern biological view on the origin of life? Share your perspective.

Completely different — biology holds that life can only come from life.

Surprisingly aligned — modern biology believes life arose from non-living matter (the "non-existent") through chemical evolution.

QUESTION 4

In the simulation experiment on "camouflage formation," the group leader scatters paper pieces of different colors (organisms) on a colored paper (environment). After multiple rounds of picking, one color of paper pieces remains the most. What does this indicate?

There were simply more paper pieces of that color to begin with.

The color of those paper pieces closely matched the environment, making them harder for predators to spot.

Paper pieces of this color have stronger offensive capabilities.

QUESTION 5

Experimental observations show that proteins, nucleic acids, carbohydrates, and lipids can concentrate and aggregate into spherical droplets in solution, with membrane-like boundaries capable of absorbing and releasing molecules. Based on this, what can you infer about the origin of life?

Primitive life may have formed through the spontaneous aggregation of organic macromolecules in the primordial ocean.

This suggests that life was brought here by extraterrestrial meteorites.

This suggests that proteins and nucleic acids can survive without water.