Evolution stuck in slime for a billion years

Wednesday 19 February 2014

Tasmanian researchers have revealed ancient conditions that almost ended life on Earth, using a new technique they developed to hunt for mineral deposits.

The first life developed in the ancient oceans around 3.6 billion years ago, but then nothing much happened. Life remained as little more than a layer of slime for a billion years. Suddenly, 550 million years ago, evolution burst back into action – and here we are today. So what was the hold-up during those ‘boring billion’ years?

According to University of Tasmania geologist Professor Ross Large and his international team, the key was a lack of oxygen and nutrient elements, which placed evolution in a precarious position. “During that billion years, oxygen levels declined and the oceans were losing the ingredients needed for life to develop into more complex organisms.”

By analysing ancient seafloor rocks, Ross and his Australian, Russian, US and Canadian colleagues were able to show that the slowdown in evolution was tightly linked to low levels of oxygen and biologically-important elements in the oceans.

“We’ve looked at thousands of samples of the mineral pyrite in rocks that formed in the ancient oceans. And by measuring the levels of certain trace elements in the pyrite, using a technique developed in our labs, we’ve found that we can tell an accurate story about how much oxygen and nutrients were around billions of years ago.”

Their research will be published in the March issue of the journal Earth and Planetary Science Letters.

“We were initially looking at oxygen levels in the ancient oceans and atmosphere to understand how mineral deposits form, and where to look for them today. That’s a focus of the Centre for Ore Deposit and Exploration Science (CODES), which we established with ARC and industry funding at UTAS in 1989,” Ross explains. “But the technology we have developed to find minerals can also tell us much about the evolution of life.”

After an initial burst of oxygen, the study plots a long decline in oxygen levels during the ‘boring billion’ years before leaping up about 750-550 million years ago. “We think this recovery of oxygen levels led to a significant increase in trace metals in the ocean and triggered the ‘Cambrian explosion of life’.

“We will be doing much more with this technology, but it’s already becoming clear that there have been many fluctuations in trace metal levels over the millennia and these may help us understand a host of events including the emergence of life, fish, plants and dinosaurs, mass extinctions, and the development of seafloor gold and other ore deposits,” says Ross.

Media Contacts

Professor Ross Large on 0418352501 or ross.large@utas.edu.au

Dr Jacqueline Halpin  Jacqueline.Halpin@utas.edu.au

Laura Boland, Science in Public, on 0408 166 426 or laura@scienceinpublic.com.au

Peter Cochrane, The Communications and Media Office, University of Tasmania (03) 6226 8518, 0429 336 328  Peter.Cochrane@utas.edu.au

The Centre for Ore Deposit and Exploration Science was established as an Australian Research Council Centre of Excellence. The study has been funded by the Australian Research Council and is collaboration with the Russian Academy of Science, University of California, the Yukon Geological Survey, Geological Survey of Western Australia, Flinders University, Museum Victoria, and Mineral Resources Tasmania.

Background information

List of materials available:

• The journal paper and abstract
• About the project
• About LA-ICP-MS
• About the Cambrian Explosion
• About Great Oxidation Events
• Data charts

Abstract and paper

Sedimentary pyrite formed in the water column, or during diagenesis in organic muds, provides an accessible proxy for seawater chemistry in the marine rock record.
Except for Mo, U, Ni and Cr, surprisingly little is known about trace element trends in the deep time oceans, even though they are critical to developing better models for the evolution of the Earthʼs atmosphere and evolutionary pathways of life.

Here we introduce a novel approach to simultaneously quantify a suite of trace elements in sedimentary pyrite from marine black shales. These trace element concentrations, at least in a first-order sense, track the primary elemental abundances in coeval seawater.

In general, the trace element patterns show significant variation of several orders of magnitude in the Archaean and Phanerozoic, but less variation on longer wavelengths in the Proterozoic. Certain trace elements (e.g., Ni, Co, As, Cr) have generally decreased in the oceans through the Precambrian, other elements (e.g., Mo, Zn, Mn) have generally increased, and a further group initially increased and then decreased (e.g., Se and U).

These changes appear to be controlled by many factors, in particular: 1) oxygenation cycles of the Earthʼs ocean–atmosphere system, 2) the composition of exposed crustal rocks, 3) long term rates of continental erosion, and 4) cycles of ocean anoxia. We show that Ni and Co content of seawater is affected by global Large Igneous Province events, whereas redox sensitive trace elements such as Se and Mo are affected by atmosphere oxygenation.

Positive jumps in Mo and Se concentrations prior to the Great Oxidation Event (GOE1, c. 2500 Ma) suggest pulses of oxygenation may have occurred as early as 2950 Ma. A flat to declining pattern of many biologically important nutrient elements through the mid to late Proterozoic may relate to declining atmosphere O2, and supports previous models of nutrient deficiency inhibiting marine evolution during this period. These trace elements (Mo, Se, U, Cu and Ni) reach a minimum in the mid Cryogenian and rise abruptly toward the end of the Cryogenian marking the position of a second Great Oxidation Event (GOE2).

The paper is available online at: www.sciencedirect.com/science/article/pii/S0012821X13007267

About the project

The paper has been produced as part of a larger project led by the Centre for Ore Deposit and Exploration Studies at the University of Tasmania and has been funded by the Australian Research Council in collaboration with the Russian Academy of Science, Flinders University, Museum Victoria, University of California, the Yukon Geological Survey and Mineral Resources Tasmania.

Several national collaborators assist with sample collection: Peter Haines and Arthur Hickman from the Geological Survey of Western Australia; Kliti Grice from Curtin University; David Huston from Geoscience Australia; and Clive Calver from Mineral Resources Tasmania.

A number of international collaborators will advise in specific areas where required: Timothy Lyons from University of California, Riverside; Valeriy Maslennikov from Institute of Mineralogy, Urals; Patrick Sack from the Yukon Geological Survey; Nick Beukes from the University of Johannesburg; Victor Melezhik from the Geological Survey of Norway; Peter Sorjonen-Ward from the Geological Survey of Finland; and Ray Coveney from the University of Missouri-Kansas City.

All analyses are to be undertaken at UTAS and through collaboration with ANU (Trevor Ireland).

Understanding concentrations of trace elements in the oceans over the past four billion years is critical to developing new models and filling knowledge gaps in the evolution of the Earth’s atmosphere, evolutionary pathways of marine life, and the formation of major mineral deposits in marine basins.

However, very few studies have focused on analysing trace elements in the ancient oceans. This study uses a new approach to measure a suite of key trace elements in the mineral pyrite within black shales dating from 3,550 million years ago to the present day. These shales developed on the ancient seafloor and can tell us much about the chemical conditions on Earth billions of years ago.

The outcome of the project will be a set of 25 evolutionary patterns for trace elements that can be related to other major Earth cycles including atmospheric oxygenation, supercontinent cycles, seafloor hydrothermal activity, pulses of evolution, mass extinction events and cycles of major ore deposits.

The project builds on eight years of research by the team, using cutting-edge LAI-CPMS technology and using techniques successfully carried out in mineral formation, which is a focus of the Centre for Ore Deposit and Exploration Science at UTAS.

In the same way that hydrothermal pyrite can be used to track changes in the chemistry of ore fluids, sedimentary pyrite can be used to track changes in the chemistry of seawater.

60 locations in viable ‘hot spots’ around the world have been sampled, and five separate lines of investigation have been used to validate the theory, including comparing published data, detailed new rock studies and new analysis of existing samples.

About the technology and the role of mass spectrometry

LA-ICP-MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry) is a powerful analytical technology for analysing solid samples.

LA-ICP-MS begins with a laser beam focused on the sample surface to generate fine particles – a process known as Laser Ablation. The ablated particles are then transported to the secondary excitation source of the ICP-MS instrument for digestion and ionization. The excited ions in the plasma torch are subsequently introduced to a mass spectrometer detector for both elemental and isotopic analysis.

LA-ICP-MS is one of the most exciting analytical technologies available because it can perform ultra-highly sensitive chemical analysis down to ppb (parts per billion) level — without any sample preparation and results are available within seconds.

It is widely used in medicine, forensics, environmental studies and more recently, industrial and biological monitoring of people involved with hazardous substances.

The Cambrian Explosion.

The Cambrian explosion was the relatively rapid appearance, around 542 million years ago, of most major animal phyla, as demonstrated in the fossil record. This was accompanied by major diversification of other organisms. Before about 580 million years ago, most organisms were simple, composed of individual cells occasionally organized into colonies. Over the following 70 or 80 million years, the rate of evolution accelerated by an order of magnitude and the diversity of life began to resemble that of today.

The Cambrian explosion has generated extensive scientific debate. The seemingly rapid appearance of fossils in the “Primordial Strata” was noted as early as the 1840s, and in 1859 Charles Darwin discussed it as one of the main objections that could be made against his theory of evolution by natural selection.

The long-running puzzlement about the seemingly abrupt appearance of the Cambrian fauna, centers on three key questions:

• Was there really a mass diversification of complex organisms over a relatively short period of time during the early Cambrian? Are we lacking evidence of what really happened?
• What might have driven such rapid change?
• What it would imply about the origin and evolution of animals?

Interpretation is difficult due to a limited supply of evidence, based mainly on an incomplete fossil record and chemical signatures remaining in Cambrian rocks.

This latest research helps to address some of these questions.

About Great Oxidation Events (GOEs)

There have been two GOEs in Earth’s history – one at 2.4 billion years ago and one at around 500 million years ago corresponding with the Cambrian Explosion.

GOEs are large increases in oxygen in the Earth’s atmosphere, and there are several schools of thought about its origin. One is that it was produced by ancient organisms that produced oxygen as a by-product of photosynthesis. In this scenario, oxygen was quickly drawn on by earth processes such as weathering, but started to build up in the atmosphere one these processes had levelled out. Another is that the oxygen-producing organisms only evolved shortly before the GOE.

Either way, the oxygen did eventually accumulate in the atmosphere, providing a new opportunity for biological diversification as well as tremendous changes in the nature of chemical interactions between rocks, sand and clay and other geological substrates and the Earth’s air, oceans, and other surface waters.

Despite the natural recycling of organic matter life had remained energetically limited until the widespread availability of oxygen. This breakthrough in metabolic evolution greatly increased free energy supply to living organisms, having a truly global environmental impact; mitochondria, the starting form of all life, evolved after the GOE.

Data chart