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The Earliest Evidence of Life

Class 7
Jun 3, 2023


If you took a trip back to when the Earth was forming about 4.6 billion years ago, you’d find a very different planet than the one we know and love today.

Earth before and now

The Earth likely began as a mass of hot, molten material that was constantly being bombarded by meteorites. As time went on, the material of Earth was sorted out into layers.


Let’s discuss this in detail.


Life on Earth began at least 3.5 to 4 billion years ago.

At first, there were only single-celled organisms on Earth as living things. Much later, multicellular organisms evolved, and then the Earth’s biodiversity increased.


The figure below shows a timeline of the history of life on Earth.

History of Life on Earth

What is the earliest evidence of any kind that life was present on Earth?


Fossils are preserved evidence of life on Earth.

Fossils come in many forms, including impressions, preserved remains, or traces of life.


Fossils typically come from hard features of an organism, such as an exoskeleton, bone, stone imprint, or shell.


Fossils provide clues on the evolution of life on Earth and allow for the study of evolution and of ancient life.

Categories of fossil types


A paleontologist is a scientist who studies fossils.

They study fossils to determine the relationships among organisms, the approximate times when life first appeared, when different organisms first lived on Earth, and when organisms became extinct.

A paleontologist

The earliest known fossil of a once-living organism belongs to the cyanobacteria.

This fossil dates back 3.5 billion years to the Precambrian era.

Cyanobacteria were one of the first lifeforms on the planet.

The fossil record of the cyanobacteria

These fossils were preserved due to the tendency of this cyanobacteria to form thickly layered structures known as stromatolites.

Fossil stromatolite

The earliest evidence that shows that life was present on Earth can be dated to 3.7 billion years ago. This record is the presence of biogenic carbon signatures in metasedimentary rocks from western Greenland.

Much evidence for the pattern of evolution and evolutionary relationships comes from fossils.

If a paleontologist finds fossils in a fairly shallow sedimentary rock layer and then finds others in a deeper sedimentary rock layer, the older fossils are usually those in the deeper sedimentary rock layer.

Oldest and youngest fossils

How Do Fossils Provide Evidence of the Past?

Most organisms decompose and leave no direct evidence of their existence. However, the parts of organisms that are preserved through permineralization, replacement, carbonization, or other methods can tell us much about when organisms lived, how they changed, and when they became extinct.

Fossils provide clues that paleontologists can use to reconstruct extinct organisms.

The locations of fossils in sedimentary rock layers can indicate the relative ages of fossils.

Paleontologists reconstructing organisms

What is the Geologic Time Scale?

Scientists use the term geologic time to represent the 4.6 billion years since the Earth formed.

The geologic time scale is a timeline that shows the Earth’s history divided into time units based on the significant events occurring at that time.

Scientists use fossils, rock layers, and their relative positions to put the Earth’s history into order.

The geologic time scale is broken into divisions and subdivisions.

The divisions are called eons, and eons are divided into eras, eras are divided into periods, and periods are divided into epochs.

For example, the Pleistocene is an epoch in the Quaternary period in the Cenozoic era in the Phanerozoic eon.

Geologic time scale
The Earliest Evidence of Life


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