Article image

When did the first animals appear on Earth? We are now one step closer to knowing the answer

The conundrum? The exact point in history when the first animals appeared on Earth. When did animals come into existence? Surprisingly, we still aren’t really sure.

This intriguing mystery that has baffled scientists since the days of Charles Darwin could be inching closer to a resolution. A new a study conducted by a team from the University of Oxford provides us with some answers.

When the first animals appear in Earth’s fossil record

The first known traces of animals can be found in fossils that date back about 574 million years. This was during the time known as the Cambrian period.

However, the sudden ‘explosion’ of these creatures during this time goes against the typically gradual pace of evolution.

This puzzle has been a topic of intense debate among scientists. This group includes Darwin himself.

Many hypothesize that animals may have evolved long before the Cambrian period. The mystery deepens when they consider the notable absence of these early animals in the fossil record.

An evolutionary ‘clock’ built on genetic mutation rates suggests animals first appeared about 800 million years ago. This would have been during the early Neoproterozoic era.

Despite this, the fossil record from this era only contains traces of microorganisms like bacteria and protists. There are no signs of any animal life.

Two big questions about the first animals on Earth need answers

This contradiction left researchers with two challenging questions. First, did the molecular clock method overestimate the evolution timeline? Or were these early animals too fragile to be preserved in the fossil record?

Dr. Ross Anderson and his team at the University of Oxford’s Department of Earth Sciences took up the challenge to solve this mystery. They performed an in-depth study of the conditions that might have preserved the earliest animal fossils.

“The first animals presumably lacked mineral-based shells or skeletons, and would have required exceptional conditions to be fossilized,” Dr. Anderson explained.

Searching for the first animals in the BST preservation

He added that some Cambrian mudstone deposits have shown exceptional preservation of even the most delicate animal tissues.

The team hypothesized that if these preservation conditions were present in Neoproterozoic rocks, their lack of fossils would imply animals simply weren’t there at that time. This period was known as Burgess Shale-Type (BST) preservation.

The researchers studied nearly 20 samples of Cambrian mudstone deposits using several analytical techniques. These included energy dispersive X-ray spectroscopy, X-ray diffraction, and infrared spectroscopy.

They compared deposits containing BST fossils with those containing only mineral-based remains. Trilobites would fit into this category.

In their analysis, the team found that fossils with BST-type preservation were especially rich in berthierine. This is an antibacterial clay. In about 90% of cases, samples containing at least 20% berthierine preserved BST fossils.

Another antibacterial clay, kaolinite, was found to bind directly to decaying tissues at an early stage. This provided a protective halo during fossilization.

“The presence of these clays was the main predictor of whether rocks would harbor BST fossils,” Dr. Anderson noted.

“This suggests that the clay particles act as an antibacterial barrier that prevents bacteria and other microorganisms from breaking down organic materials.”

Searching for the first animals in Neoproterozoic deposits

The team then used these methods to examine samples from many fossil-rich Neoproterozoic mudstone deposits. Most samples lacked the compositions necessary for BST preservation.

There were exceptions to this found in three deposits in Nunavut, Canada, Siberia, Russia, and Svalbard, Norway. These samples had compositions nearly identical to Cambrian BST rocks. Surprisingly, they didn’t contain any animal fossils.

Dr. Anderson clarified, “Similarities in the distribution of clays with fossils in these rare early Neoproterozoic samples and with exceptional Cambrian deposits suggest that, in both cases, clays were attached to decaying tissues. Conditions conducive to BST preservation were available in both time periods. This provides the first ‘evidence for absence’ and supports the view that animals had not evolved by the early Neoproterozoic era, contrary to some molecular clock estimates.”

This study suggests that the origin of animals might not go back further than approximately 789 million years. This dates to the youngest estimated age of the Svalbard formation.

Next steps in the search for the first animals on Earth

The research team now plans to investigate progressively younger Neoproterozoic deposits with conditions suitable for BST preservation.

They aim to pinpoint the age of rocks where animals are absent from the fossil record because they genuinely weren’t there. This does not include conditions that simply failed to preserve the fossils.

The team also intends to conduct laboratory experiments to understand how clay and organic matter interact during BST preservation.

Dr. Anderson concluded, “Mapping the compositions of these rocks at the microscale is allowing us to understand the nature of the exceptional fossil record in a way that we have never been able to do before. Ultimately, this could help determine how the fossil record may be biased towards preserving certain species and tissues, altering our perception of biodiversity across different geological eras.”

To clarify, when we talk about ‘animals’, we’re referring to multicellular, eukaryotic organisms belonging to the biological kingdom Animalia.

They feed on organic matter, breathe oxygen, reproduce sexually, and have specialized sense organs and nervous systems. This enables them to respond quickly to stimuli.

More about the Ediacaran Period

The Ediacaran Period, part of the Neoproterozoic Era, is a significant span of time in Earth’s history. It extends from about 635 to 539 million years ago.

It was named after the Ediacara Hills of South Australia. That is where some of the period’s characteristic fossils were first discovered.

Notably, the Ediacaran Period is the last geological period before the Cambrian. The Cambrian era is famous for its “Cambrian Explosion” of life.

The boundary marking the end of the Ediacaran and the beginning of the Cambrian is significant. It denotes the first appearance of many major types of animals in the fossil record.

However, the Ediacaran Period has its own distinct characteristics and importance:

Life in the Ediacaran Period

This period is known for the appearance of the Ediacaran biota. These are large, complex multi-celled organisms which were unlike any life form seen previously.

Many of these organisms were soft-bodied and display a unique range of forms. Some resembled modern groups of animals. Others are completely unique to the Ediacaran.

The nature and classification of the Ediacaran biota have been subjects of much debate. Some of these organisms appear to have had no modern equivalents. This makes their classification difficult. There are various theories suggesting these organisms might be lichens, fungi, or even an extinct kingdom of life.

The Ediacaran Environment

The start of the Ediacaran Period is marked by the end of the Marinoan glaciation. This was one of the most severe ice ages in Earth’s history. It led to a “Snowball Earth” scenario.

As the planet warmed and the ice retreated, the seas of the Ediacaran Period likely covered much of the Earth’s surface. At that time, most landmasses probably existing as small, scattered islands.

The Ediacaran oceans were likely low in oxygen, limiting the complexity and diversity of life forms. The end of the period is marked by a rise in oxygen levels. Some scientists believe this may have contributed to the diversification of life in the subsequent Cambrian Explosion.

Fossil Evidence

Ediacaran fossils are unique. Unlike the later fossils from the Cambrian period and onwards, which were mostly preserved in a mineralized form, many Ediacaran fossils were preserved as casts and molds in sediment.

This is likely due to the soft-bodied nature of many Ediacaran organisms. Some of the most famous sites for these fossils include Mistaken Point in Newfoundland, the White Sea area in Russia, and the Ediacara Hills in Australia.

The Ediacaran-Cambrian Transition

There is a lot of debate about what caused the transition from the Ediacaran to the Cambrian periods. One popular theory is the rise in oxygen levels. This could have facilitated the evolution of more complex, oxygen-dependent organisms.

Another theory suggests a mass extinction event at the end of the Ediacaran. This would have led to the disappearance of most Ediacaran biota and paved the way for the Cambrian explosion of life.

In summary, the Ediacaran Period represents a key time in Earth’s history. It marks the rise of complex multicellular life, setting the stage for the profound biodiversity of the Cambrian Explosion. It’s an area of active research and continued discovery in the field of paleontology.

More about the Cambrian period

The Cambrian period is one of the most significant periods in the Earth’s history. Lasting from about 541 to 485.4 million years ago, it’s the first geological period of the Paleozoic Era.

It followed the end of the Ediacaran Period, leading into the Ordovician Period. Here’s what we know about this intriguing phase of our planet’s history:

Cambrian Explosion

One of the most notable aspects of the Cambrian Period is what’s known as the “Cambrian explosion.” This refers to the sudden appearance in the fossil record of a wide range of complex, multicellular organisms.

This marked a major transition in the history of life on Earth. Prior to the Cambrian explosion, most life forms were relatively simple. They were composed of individual cells or small colonies of cells.

Diversification of Life

During the Cambrian explosion, nearly all the major groups of animals first appeared in the fossil record. This includes the first appearances of arthropods, mollusks, brachiopods, annelids, and echinoderms, among others.

Many of these organisms had hard shells or exoskeletons. This increased their chances of being preserved as fossils.

Geological Changes

During the Cambrian, the supercontinent Pannotia began to break up. The continents as we know them today started to form.

Sea levels were higher than they are today. This led to extensive shallow seas. In these warm, shallow waters, the conditions were ripe for the rapid evolution and diversification of life.

Fossil Evidence

The Cambrian period has left a rich fossil record. Some of the best known fossil sites from this time include the Burgess Shale in Canada and the Chengjiang Maotianshan Shales in China.

These sites are notable for their exceptional protection of soft bodied creatures. These provide a complete view of Cambrian marine life.

Atmosphere and Climate

The Cambrian atmosphere was probably rich in oxygen. This may have supported the diversification and complex development of animal life.

The climate was also likely warmer than today. There is no evidence of glaciations that would suggest cooler periods.

Predation and Evolution

The evolution of predation, with animals eating other animals, is believed to have had a significant impact during the Cambrian.

The presence of predators led to an ‘arms race’ between predators and prey. This drove the evolution of features such as shells, spines, and other defensive structures, as well as more effective hunting skills.

Extinction Event

The end of the Cambrian period is marked by a series of extinction events that wiped out many brachiopods and conodonts. It also severely reduced the number of trilobite species.

Importance of the Cambrian Period

The Cambrian is of immense scientific interest. It provides critical evidence about the early evolution of animal life, ecosystem dynamics, and changes in the Earth’s climate and geography.

The Cambrian also represents a key period in our planet’s history, when the foundations for much of the later life forms were established.

In summary, the Cambrian Period was a critical phase in Earth’s history. It was marked by remarkable evolutionary advancements and the spread of diverse life forms. Finally, it set the stage for the further development and complexity of life in the following geological periods.

News coming your way
The biggest news about our planet delivered to you each day