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Earth’s Major Events – The Last Ice Age and Earliest Fossils

Class 7
Jun 5, 2023

Last Ice Age and Earliest Fossils


Scientists have predicted that the Earth formed along with the solar system around 4.6 billion years ago. Several scientists have put forth various hypotheses regarding the origin of Earth. “Nebular Hypothesis” is the most popular theory of the origin of Earth. It was proposed by Immanuel Kant, a German philosopher.

This theory states that the solar system is formed from a big cloud of dust and gas known as a nebula. Scientists have predicted that around 3 billion years ago, the first life on Earth appeared. It was a tiny unicellular prokaryote.

Scientists have identified stone imprints of these microbes. The remains or traces of ancient life that have been preserved by natural processes are known as “fossils.” Fossils are important evidence of evolution. They act as an important tool for understanding geological history.

Scientists make use of these fossils to calculate the geological time scale. The geological time scale provides the calendar for the events of Earth’s history. It divides Earth’s history into geological time periods. Based on fossil records, scientists have classified geological time scales into four subdivisions, namely – Eons, Eras, periods, and epochs.

History of the Earth


Major events of Earth’s history

The Last Ice Age

The last ice age is known as the Pleistocene epoch. It began around 2.6 million years ago and ended 11,700 years ago. The Pleistocene epoch is also referred to as the “Great Ice Age.” Scientists have predicted that during this epoch, glaciers and extensive ice sheets formed repetitively on landforms. It is also predicted that humans evolved during the Pleistocene epoch and spread across most parts of the Earth before the end of the epoch. The current geological epoch is known as the “Holocene Epoch.” This epoch is also known as the “Anthropocene Epoch” (Greek: Anthropocene – recent age of man), “Human era.”

The most important characteristic of this period is the global changes that are caused due to human activity. During this period, human activity has produced a significant impact on the ecosystem and Earth’s climate.

Planet Earth through the ages

Evolution of Holocene Epoch


Evolution of Holocene Epoch


The remains or traces of ancient life that have been preserved by natural processes are known as “fossils” (Latin: fossils – something dug up). Fossils are important evidence of evolution. Fossils are known as our window to the past. They also help us to learn about the future.

Examples of fossils: Bones, shells, impressions of animals/bacteria on stones, exoskeletons, petrified wood, hair, coal, etc.

How are Fossils Formed?

During ancient times, when the remnants of animals or plants became hardened and fixed within a sedimentary rock or volcanic ash, it led to the formation of fossils. When the remnants of living organisms get saturated and hardened with minerals like calcite or silica, they get transformed into stone.

Importance of Fossils

The study of fossils and the evolution of life on Earth is known as “paleontology.”  Fossils provide evidence about ancient life on Earth. Scientists use fossils to understand the process of evolution. They also provide evidence about the changes in Earth’s surface over time.

Fossils provide information about ancient environments and climates. Fossils act as important evidence to calculate the age of rocks. Geologists make use of fossil records to create geological maps and discover new mineral deposits.

Types of Fossils

The five types of fossils are:

  • Body fossils
  • Molecular fossils
  • Trace fossils
  • Carbon fossils
  • Pseudo fossils


Fossil formation

Various life forms on Earth during different eras

Fossils of different periods

Earliest Fossils

Fossils serve as an important element in understanding the evolution of Earth and various life forms on Earth. The following are some of the oldest fossils identified so far.

Hematite Tubes

Hematite tubes are considered the oldest fossils in the world. In the year 2017 in Canada, scientists identified tube-like bacteria on hematite ore. These fossils are estimated to be around 3.7 to 4.2 billion years old.


Stromatolites are widely accepted as the oldest fossils. The oldest stromatolite is estimated to be around 3.5 billion years old. These fossils were formed by cyanobacteria, the ancient blue-green algae. Most of the stromatolites identified so far are old and dead. In 1956, extremely rare living stromatolites were identified from the Hamelin pool of Western Australia.

Seaweed-like Fossils

These fossils were identified in the year 2016 by researchers from China. These fossils are considered important evidence of ancient multi-cellular life forms. Researchers have identified around 167 fossils, and they were estimated to be around 1.56 billion years old.

Pikaia Fossils

Pikaia fossils were discovered by Charles Walcott in Canada during the year 1911. Since these fossils were discovered in a mountain named Pika Peak, they were named so. These fossils are estimated to be around 523 million years old and are considered evidence of the oldest known ancestor of modern vertebrates.


These are considered to be the oldest trilobite fossils. They are estimated to be around 525 – 500 million years old. They were identified in Southern Australia and China. Redlichiida were found to have a flat, oval-shaped exoskeleton. These are considered the ancestor of all trilobite species.


These fossils were identified in Canada. They are estimated to be around 505 million years old. These are the fossils of primitive fish. These are used as evidence to study early jaw development in fishes.


These are the fossils of the earliest-known fungus. They were discovered in Scotland during the year 2016. These fossils are estimated to be around 440 million years old. Tortotubus are known to be the oldest fossils of land-based organisms.

Rhyniognatha First

These are the fossils of the world’s oldest insect. They were discovered in 1920 in Scotland. These fossils are estimated to be around 400 million years old. Rhyniognatha is considered to be one of the first animals to arrive on land. Scientists make use of these fossils to study the development of wings in insects.

Hematite Tubes



Seaweed-like Fossils


Pikaia Fossils

Earliest Fossils

last ice age and earliest fossils


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