Author: admin

Date:

September 2, 2025

Source:

NASA

Summary:

Webb, Hubble, and SPHEREx are joining forces to study the interstellar comet 3I/ATLAS, revealing details about its structure and chemistry. The comet isn’t dangerous, but it’s offering scientists a rare chance to explore material from outside our solar system.

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What’s the link between an exploding star, climate change and human evolution? Francis Thackeray, who has researched ancient environments and fossils for many years, sets out his ideas about what happened in the distant past – with enormous consequences.

Global cooling that happened millions of years ago was thought to be the result of ocean currents. He suggests instead it could have been due to the impacts of remnants of supernovae. The timing of supernovae, climate changes and species evolution coincides.

What is your supernova hypothesis?

My hypothesis is that remnants of a supernova – an exploding star – had an impact on the Earth’s past climate, causing global cooling, between 3 million and 2.6 million years ago and that this indirectly affected the evolution of hominins (ancient relatives of humans).

How does this change assumptions held until now?

It has been considered by some that global cooling in the Plio-Pleistocene might have been due to changes in ocean currents. This may well be correct to some extent, but I think that the supernova hypothesis needs to be explored.

It’s super-exciting to think that our evolution may to some extent be associated with supernovae as part of our dynamic universe.

How did you come to your supernova hypothesis?

Supernovae include stars which are extremely massive (as much as five times the mass of our Sun) and have reached the end of their stellar evolution. These explosions are rare. On average, within our galaxy (the Milky Way), only one or two per century are visible from Earth as temporary bright stars.

As a result of such explosions, material is expelled into outer space at almost the speed of light. Chemical elements are formed, including a kind of iron (the element Fe) known as isotope Fe-60. It has 26 protons and as many as 34 neutrons.

Traces of Fe-60 iron isotopes from supernovae within the last ten million years have been discovered on Earth in marine deposits such as those drilled in cores in the east Indian Ocean.

Read more:
Our oceans give new insights on elements made in supernovae

The deep-sea deposits with Fe-60 can be dated using radioactive elements which decay at a known rate. This is called radiometric dating.

There was a regular increase in extremely small traces of Fe-60 for the period between 3 million and 2.6 million years ago. We know this from data published by Anton Wallner and his colleagues. Since this is a linear trend I have been able to extrapolate back to 3.3 million years when initial cosmic rays may have first hit Earth. I have proposed in the Quest magazine that this initial cosmic impact correlates with a major glaciation (cooling) event called M2 in an otherwise warm period.

A “near earth” supernova could have produced cosmic rays (radiation from outer space) which might have caused a reduction in the earth’s ozone layer. Increased cloud cover associated with cosmic radiation could have been a factor related to changes in global climate. Specifically, the change would have been global cooling.

This cooling would have affected the distribution and abundance of plant species, in turn affecting that of animals dependent on such vegetation.

What potential new insights does the hypothesis give us into human evolution?

Populations of Australopithecus may have been indirectly affected by the decrease in temperature.

Australopithecus is the genus name for distant human relatives which lived in Africa in geological periods called the Pliocene and Pleistocene. The boundary between these time intervals is 2.58 million years ago. At that time, certain species went extinct. The period coincides closely with the maximum of Fe-60 in marine deposits and a change in Earth’s magnetic field.

The first fossil of Australopithecus to be described, 100 years ago, was placed by the palaeontologist Raymond Dart in a species called A. africanus. Dubbed the “Taung Child”, it was discovered in South Africa. Its biochronological age, recently based on mathematical analyses of tooth dimensions, is about 2.6 million years – at the Plio-Pleistocene boundary.

It cannot be concluded that the death of the Taung Child was directly caused by a supernova. This would be far-fetched. There is in fact evidence that this individual, about 3 years old, was killed by an eagle.

However, it is plausible to suggest that in Africa, in the Plio-Pleistocene, populations of Australopithecus were affected by a decrease in temperature affecting the distribution and abundance of vegetation and the animals dependent on it.

Recently, a new species of Australopithecus (as yet not named, from Ledi-Geraru) has been discovered in Ethiopia, in deposits dated at about 2.6 million years ago – also the time of the maximum in Fe-60 in deep-sea deposits.

The appearance of the genus Homo is close to the Plio-Pleistocene boundary, reflected by fossils reported recently by Brian Villmoare and his colleagues and well dated at about 2.8 million years ago. The origin of Homo may relate to changes in temperature and associated changes in habitat, as recognised five decades ago by South African palaeontologists Elisabeth Vrba and Bob Brain, although they emphasised a date of 2.5 million years ago.

Is it possible that cosmic radiation stimulated genetic changes?

I have been told by my peers that I am inclined to think “out of the box”. Well, in this case I would like to propose a “hominoid mutation hypothesis”. The hypothesis states that the speciation of hominoids (including human ancestors and those of chimpanzees and gorillas) was to some extent associated with mutations and genetic variability caused by cosmic rays.

It is interesting to consider the possibility that the origin of our genus Homo relates in part to cosmic radiation. Going deeper back in time, Henrik Svensmark has demonstrated that there is a correlation between supernova frequency and speciation (increased biodiversity associated with the evolution of new species), for the last 500 million years (the Phanerozoic period). I think it’s entirely possible that one important cause behind this correlation was the mutagenic (mutation-causing) effect of cosmic rays on DNA, such that rates of speciation exceeded those of extinction.

Read more:
Exploding stars are rare but emit torrents of radiation − if one happened close enough to Earth, it could threaten life on the planet

In hominoids, cosmic rays could have contributed not only to global cooling but also to genetic changes, with subsequent anatomical (morphological) changes related to speciation.

If we go back to about 7 million years ago (when Fe-60 again reflects supernova activity), we would expect to find fossils that are close to a common ancestor for chimpanzees and humans. In terms of the hominoid mutation hypothesis, the split could have been associated with cosmic radiation. One hominoid species about 7 million years old is Sahelanthropus (discovered by Michel Brunet in Chad). In my opinion this species is very close to the common ancestor for Homo sapiens (us) and chimps.

Sixty percent of global land is outside safe biosphere limits, with human use of biomass driving widespread ecological strain.

A new study provides the first detailed mapping of the planetary boundary known as “functional biosphere integrity,” tracing its status across centuries and in specific regions. The analysis shows that 60 percent of the world’s land surface has already moved beyond the safe operating range, with 38 percent falling into the category of high risk. The research was conducted by the Potsdam Institute for Climate Impact Research (PIK) in collaboration with BOKU University in Vienna and published in the journal One Earth.

Functional biosphere integrity describes the capacity of the plant world to help regulate the stability of the Earth system. To do so, vegetation must generate sufficient energy through photosynthesis to sustain the circulation of carbon, water, and nitrogen that underpins ecosystems and their interconnected processes, even under conditions of intense human disturbance.

Alongside biodiversity loss and climate change, this measure of integrity forms one of the central elements of the Planetary Boundaries framework, which defines the conditions necessary for a safe operating space for humanity.

“There is an enormous need for civilization to utilize the biosphere – for food, raw materials and, in the future, also for climate protection,” says Fabian Stenzel, lead author of the study and member of the PIK research group Terrestrial Safe Operating Space. “After all, human demand for biomass continues to grow – and on top of that, the cultivation of fast-growing grasses or trees for producing bioenergy with carbon capture and storage is considered by many to be an important supporting strategy for stabilizing the climate. It is therefore becoming even more important to quantify the strain we’re already putting on the biosphere – in a regionally differentiated manner and over time – to identify overloads. Our research is paving the way for this.”

Two indicators to measure the strain and the risk

The research builds on the most recent update of the Planetary Boundaries framework, released in 2023. “The framework now squarely puts energy flows from photosynthesis in the world’s vegetation at the center of those processes that co-regulate planetary stability,” explained Wolfgang Lucht, head of PIK’s Earth System Analysis department and coordinator of the study. “These energy flows drive all of life – but humans are now diverting a sizeable fraction of them to their own purposes, disturbing nature’s dynamic processes.”

The resulting strain on the Earth system can be assessed by examining how much of natural biomass productivity is redirected for human use—such as harvested crops, timber, and plant residues—as well as by the decline in photosynthetic activity caused by land conversion and soil sealing. To complement this, the study also introduced a second key measure of biosphere integrity: an indicator of ecosystem destabilization risk, which tracks large-scale structural shifts in vegetation along with imbalances in the water, carbon, and nitrogen cycles.

Europe, Asia, and North America are particularly affected

Based on the global biosphere model LPJmL, which simulates water, carbon, and nitrogen flows on a daily basis at a resolution of half a degree of longitude/latitude, the study provides a detailed inventory for each individual year since 1600, based on changes in climate and human land use.

The research team not only computed, mapped, and compared the two indicators for functional integrity of the biosphere, but also evaluated them by conducting a mathematical comparison with other measures from the literature for which “critical thresholds” are known. This resulted in each area being assigned a status based on local tolerance limits of ecosystem change: Safe Operating Space, Zone of Increasing Risk, or High Risk Zone.

The model calculation indicates that worrying developments began as early as 1600 in the mid-latitudes. By 1900, the proportion of global land area where ecosystem changes went beyond the locally defined safe zone, or were even in the high-risk zone, was 37 percent and 14 percent, respectively, compared to the 60 percent and 38 percent we see today. Industrialization was beginning to take its toll; land use affected the state of the Earth system much earlier than climate warming. At present, this biosphere boundary has been transgressed on almost all land surface – primarily in Europe, Asia, and North America – that underwent strong land cover conversion, mainly due to agriculture.

PIK Director Rockström: Impetus for international climate policy

“This first world map showing the overshoot of the boundary for functional integrity of the biosphere, depicting both human appropriation of biomass and ecological disruption, is a breakthrough from a scientific perspective, offering a better overall understanding of planetary boundaries,” says Johan Rockström, PIK Director and one of the co-authors of the study. “It also provides an important impetus for the further development of international climate policy. This is because it points to the link between biomass and natural carbon sinks, and how they can contribute to mitigating climate change. Governments must treat it as a single overarching issue: comprehensive biosphere protection together with strong climate action.”

Reference: “Breaching planetary boundaries: Over half of global land area suffers critical losses in functional biosphere integrity” by Fabian Stenzel, Liad Ben Uri, Johanna Braun, Jannes Breier, Karlheinz Erb, Dieter Gerten, Helmut Haberl, Sarah Matej, Ron Milo, Sebastian Ostberg, Johan Rockström, Nicolas Roux, Sibyll Schaphoff and Wolfgang Lucht, 15 August 2025, One Earth.
DOI: 10.1016/j.oneear.2025.101393

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