Question

How was the Earth formed? How did scientists compute the age of Earth?

Answer 1

The formation of the Earth is thought to have occurred approximately 4.5 billion years ago as part of the early Solar System. The most widely accepted theory for the Earth's formation is known as the nebular hypothesis. According to this hypothesis:

1. A giant molecular cloud, consisting of gas and dust, began to collapse under its own gravity.
2. The collapse of the cloud led to the formation of a rotating disk called the protoplanetary disk.
3. Within this disk, particles started to collide and stick together, forming larger objects known as planetesimals.
4. Over time, these planetesimals continued to grow through collisions and gravitational accretion, eventually forming protoplanets.
5. One of these protoplanets grew to become the Earth through continued accretion of material and the eventual formation of a spherical shape.
6. The process of differentiation occurred, where denser materials sank toward the center, forming the Earth's core, while lighter materials rose to the surface, forming the mantle and crust.

The age of the Earth has been determined using various scientific techniques. The most prominent method is radiometric dating, which relies on the decay of radioactive isotopes. Here's a general overview of the process:

1. Certain isotopes found in rocks and minerals undergo radioactive decay at a known rate. The decay involves the transformation of parent isotopes into daughter isotopes.
2. By measuring the ratio of parent isotopes to daughter isotopes in a sample, scientists can determine the amount of time that has elapsed since the rock or mineral formed.
3. Different radioactive isotopes have different half-lives, which is the time it takes for half of the parent isotopes to decay. Scientists use isotopes with appropriate half-lives for dating different types of rocks and minerals.
4. By analyzing samples from various locations on Earth and using multiple isotopic systems, scientists have obtained consistent ages and established that the Earth is approximately 4.5 billion years old.

Some of the commonly used radiometric dating methods for determining the age of Earth materials include uranium-lead dating, potassium-argon dating, and rubidium-strontium dating.

Additionally, other techniques, such as studying the ages of Moon rocks brought back by Apollo missions and meteorites, have provided additional evidence supporting the estimated age of the Earth.