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Imagine a 1 square km section (including a suitable depth of soil - maybe 100m?) of a contemporary rainforest is transplanted onto the Earth in a time a few million years before the Cambrian explosion (540 mya), to an area which approximates the same surface temperature and precipitation as the area experiences on earth today.

Could we expect the contemporary plants and animals to survive / thrive during that time, and would they out-compete the native creatures?

Assuming they survive, can anyone speculate on how long it would take for 'contemporary' life to come to dominate the whole planet (or at least the land parts of it)?

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    $\begingroup$ Depends of what exactly is transported. The was no soil in the Precambrian, no land-based life forms; land surface was bare rock: so the trees in the rainforest would instantly fall down and die unless a fairly hefty amount of soil is transported with them... Moreover, there being no soil, the expansion of the "modern" enclave would be very very very slow. One square kilometer is too small to sustain any large animal, so that any animal species larger than a sparrow would certainly die off in the centuries and millennia of extremely slow expansion. $\endgroup$
    – AlexP
    Aug 24, 2020 at 12:56
  • $\begingroup$ I've added a clarification that soil would be transported too $\endgroup$
    – Neil Tarrant
    Aug 24, 2020 at 13:01
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    $\begingroup$ Isn't this a bit presumptuous to assume contemporary = terrestrial? Anyways, the atmosphere was unsuitable in the pre-cambrian. Not enough oxygen and not enough ozone as far as we know. Plants can be picky...my pitcher plant fries if I move it from beside the window to outside without letting it acclimate first, and that is in conditions where it is supposed to live. $\endgroup$
    – DKNguyen
    Aug 24, 2020 at 14:21
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    $\begingroup$ @AlexP: The land surface wouldn't be entirely bare rock, since erosional processes would have made gravel, sand, silt, and mud. Not to mention volcanic ash. There would almost certainly have been microbial life in some of those, and an oxygenated atmosphere in the late Precambrian: ttps://en.wikipedia.org/wiki/Precambrian#Subdivisions Expansion of life into new areas isn't all that slow: consider the recolonization of volcanic zones (e.g. Mt. St. Helens) after an eruption. $\endgroup$
    – jamesqf
    Aug 24, 2020 at 21:06
  • $\begingroup$ @AlexP Certain animals that can eat sea life might be able to survive as well. $\endgroup$
    – nick012000
    Aug 25, 2020 at 6:14

8 Answers 8

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DESTINATION UNKNOWN:

The precambrian represents 90% of Earth's history, and so is a huge and amazingly variable time. Even in the later times, this period is often assumed to be extremely volcanic with lots of major impact events, but the record is very poor as to what really happened. Tuesday could be mass extinction day, but there was no one to record it, and no life of note to care.

There are a lot of things we don't know with certainty about the precambrian period that affect your question. Traditionally, the atmosphere in this time was assumed to be very low in oxygen, but there's debate on this subject. Much of your life could die within minutes of arrival, including essential insects. There may have been lethal doses of trace gasses that would kill your plants instantly. Conventional plants are used to our air mix, and a sudden change would probably kill them, even if they were somehow self-conserving enough to hold most of their oxygen for internal use (a big if). I'm not certain at what point the atmosphere was able to screen out enough radiation to allow plants to grow outside water, but there wouldn't be an ozone layer like we think of to protect them.

A rainforest requires a lot of steady water. We know almost nothing about the weather or water cycle of the period, but it's unlikely to have been stable or consistent. Land would not retain rainfall well. Your forest would need to land in the luckiest place on Earth (literally) to even get the water it needed.

The most likely survivors of your drop would be bacteria, and they would potentially be quite advanced compared to their local ancestors. This doesn't guarantee they would live - local conditions could be bad, and local bacteria would be well adapted to the conditions then and there. It is not impossible that the addition of modern bacteria could have a chilling effect on eukaryotic evolution. Better adapted bacteria might outcompete early eukaryotes for essential survival niches.

Any introduction of modern life to the precambrian environment would need to more resemble terraforming than a random drop of land into an ancient world. Specially adapted lichens would likely hold up well, as would some single-cell animals, possibly some sponges selected for local foods and conditions and various sea plants and planktons selected and/or modified for local conditions. Your time travellers would need favorable starting conditions and broad distribution to avoid catastrophes. After a few million years, your inserted select organisms may have transformed things enough to allow more advanced plants, animals and fungi to be introduced.

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    $\begingroup$ OP is asking about Cambrian, not pre-Cambrian. $\endgroup$
    – DKNguyen
    Aug 24, 2020 at 14:09
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    $\begingroup$ @DKNguyen The question states BEFORE the cambrian explosion, which is by definition, the precambrian. $\endgroup$
    – DWKraus
    Aug 24, 2020 at 14:11
  • $\begingroup$ Oh so it does. In which case I think nothing would survive without the wet bosom of the ocean. $\endgroup$
    – DKNguyen
    Aug 24, 2020 at 14:12
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    $\begingroup$ "a few million years before the Cambrian explosion (540 mya)" - that specifies a relatively narrow timespan. $\endgroup$
    – Alexander
    Aug 24, 2020 at 17:29
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    $\begingroup$ @DWKraus - the time-from of a few million years before the Cambrian explosion was always specified in the question. $\endgroup$
    – Neil Tarrant
    Aug 25, 2020 at 16:11
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The soil would be lacking a lot if not all of the organic part which makes the difference between a proper growing ground and simply crushed rocks.

This would mean that any exchange with the surrounding environment would likely impoverish the transplanted biome, affecting its wellness.

Since a (rain)forest is the final stage of a sequence of steps starting with pioneering plants, I am confident most of the plants would suffer from the non favorable environment and wither. This would affect all the food chain, which is based on those plants.

I am not sure that the modern biome would outcompete the native lifeforms, for the simple reason they are better used to those particular conditions.

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    $\begingroup$ Even the pioneering plants (there are probably some in odd corners) will find it hard to grow on earth in that era. On the other hand, a wide open field for growth will create an enormous evolutionary pressure to adapt and spread -- and change to fit the new environment. $\endgroup$
    – Mary
    Aug 24, 2020 at 12:38
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    $\begingroup$ I think we need to look every further than pioneering plants to the bacteria, micro-organisms etc. which make up soil needing to colonise the ancient regolith (and I've edited my question to clarify that they are included). Presumably these live in a complicated, interdependent web, but possibly at least some would be able to survive, and slowly, over hundreds if not thousands of years convert the otherwise barren soil to something more contemporary? $\endgroup$
    – Neil Tarrant
    Aug 24, 2020 at 13:06
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    $\begingroup$ A rainforest is probably the second-best choice for transplanting, after a desert or tundra lichen colony: since most of the nutrients are locked up in the plants, everything's reasonably well-adapted to growing in poor soil. $\endgroup$
    – Mark
    Aug 24, 2020 at 22:06
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If the rainforest is transported with all the supporting ecosystem (bacteria, worms, bees etc.) and if it is transported to a favorable climate, then yes, it will thrive.

Some of the species would go extinct, but the rest would be very comfortable. There is just nothing that can threaten this patch of rainforest in late Precambrian.

What would be the problem for the modern life is to expand out of this little foothold in the ancient world. As other people have mentioned, Precambrian landscape was very barren. Most of the plant and animal species of the rainforest just can't live there. But a few of them can. So autotrophic species like mosses and lichen will start slow expansion. If will take many thousands of years for them to expand over the surface of the Earth, but eventually they will get there - simply because there's nothing to stop them. Their competitors, ancient lifeforms are hundreds of million of years behind in terms of surface adaptation.

After primary producers would colonize barren world, other organisms, like bacteria and fungi will follow. Eventually, a soil will form and modern life will colonize entire surface of the Earth. I'm sure that will happen in less than one million years.

It is a very good question what would be happening in the seas. At first, rainforest life would have no adaptation to live in sea water. But evolutionary pressure would undoubtedly make seawater organisms from freshwater and terrestrial ones. Whales and dolphins had already walked this way, and in Precambrian, some species will evolve to eventually dominate the seas. That should take more than one million years, and native species may offer some stiff competition.

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For most on-land contemporary plants and animals Earth would by lifeless - all life was at narrow strip in seas and lakes along the coast. All landmasses were just barren rocks were even deserts plants wouldn't live. So all of this 1 sq miles rainforest would just die out qickly without even having contact with precambrian life.

BUT there is some water and surface based plankton life in rain forest. I.e. some unicellular algae and very small crustacean. These are extrimly advanced for this time. And if they somehow managed to get into water (like by the wind) with then plankton - they could form new modern-like plankton layer and than evolve into something.

So all we can get at best-case scanario is premature Cambrian explosion with slightly different ways of evolution. This can dramatically change all the species and all biological history . Like abscence of dinosaurs, or mammals, or both - crocodiles rules the world!

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  • $\begingroup$ Would 1 kilometre square not be a sufficiently large community for at least some plants-life (even if primitive) to survive for some length of time? Enough for microbial life to start converting those barren rocks into something more soil-like? $\endgroup$
    – Neil Tarrant
    Aug 24, 2020 at 13:08
  • $\begingroup$ @NeilTarrant: Yes, an area one square kilometer with suitable soil is ample for some plant species to survive. In time, those plants (and fungi, and microbes) would produce more soil and the enclave would expand. Some small animal species would likely survive too. $\endgroup$
    – AlexP
    Aug 24, 2020 at 13:20
  • $\begingroup$ @NeilTarrant it would suvive for couple of sesons at best. Forest would rapidly die at edges and soil would dry and weathering would take it away. Plants, espesially at rainforest are very sensetive to outer conditions. So forest would just rapidly shrink. Only microorganisms have any chances to spread. Just imagine putting that forest in the middle of Sahara desert! $\endgroup$
    – ksbes
    Aug 25, 2020 at 7:39
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Will the Contemporary plants survive? You're asking the wrong question

In one way the Earth's diversity has dropped over time. We have fewer flora and fauna species. But in another... We have more bacteria, more viruses, than ever before.

And you just dropped all that in the middle of a time where the defenses haven't developed.

By the toll of a billion deaths, man had plants have earned his their immunity, his their right to survive among this planet's infinite organisms, and that right is ours theirs against all challenges, for neither do men plants live nor die in vain. (Morgan Freeman, War of the Worlds (2005))

The modern flora with all of its disease, parasitic insects, and animal life — everything that could be found within a square Km that's had a bazillion years to develop immunities and symbiotic relationships — would likely thrive in the Cambrian era. Heck, even the Cambrian atmosphere would be conducive (I think) to rapid growth.

On the other hand, it's plausible (if not down right expected) that you destroyed the Cambrian era, creating a universe-ending paradox.

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    $\begingroup$ But what about the fact that in most cases area was completely sterile before forest arival? So biomes wouldn't even have a direct contact. $\endgroup$
    – ksbes
    Aug 25, 2020 at 7:43
  • $\begingroup$ @ksbes One assumes that the question must necessarily drop the square km of rain forest where there is life - otherwise the question has no point. $\endgroup$
    – Join JBH on Codidact
    Aug 25, 2020 at 16:41
  • $\begingroup$ but at that period there were no life on land. May be even no fungus or bacteria. And dropping rainforest into ocean is not the greatest idea $\endgroup$
    – ksbes
    Aug 26, 2020 at 9:29
  • $\begingroup$ @ksbes Yes and no. Science still has a poor view of exactly what happened that far back as it relies solely on fossilized records and fossilized grass, for example, is hard to come by. Science admits that it's view is skewed because the easily fossilized critters (like trilobites) had hard shells that made them easy to fossilize. Were there trees? Probably not. Were there grasses? Probably. Were grasses everywhere? Probably not. But who knows? What certainly is true is that even if that square km of rainforest died, the bacteria, viruses, etc. it brought would not - and they'd be a plague. $\endgroup$
    – Join JBH on Codidact
    Aug 26, 2020 at 14:56
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If you read wikipedia, about the last ~ 94MY of Precambrian, which is called Ediacaran, and read about Ediacaran biota:

  • there was little free oxygen before Ediacaran, until all free iron "rusted"
  • no life on land - even lichens are disputed
  • even first insects are from Devonian period, 200MY AFTER Edicarian
  • several suspected Snowball Earth glaciations. Even if surface is not fully covered by ice/glaciers like during Marinoan glaciation, it would be too cold for rainforest

So chances of your replanted contemporary life surviving back then is slim to none.

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Based on the current understanding of Earth's climate history, transporting said section of rain forest back to the Ediacaran a few million years before the Cambrian results in either the immediate destruction of the rainforest as it materializes in the middle of an ice sheet during the Baykonurian glaciation, or everything except microorganisms dying soon afterward despite missing the ice because of the cold climate.

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Rainforest plants would do OK. Bugs would thrive!

Long before there were plants on land, there were microbial mats. The heyday of marine microbial mats was well over a billion years ago, with the evolution of multicellular grazers and tunnelers pushing them from dominance.

On the land the microbial mats of cyanobacteria and other bacteria did well. There are also fossil traces of these from over a billion years ago. Microbial mats of this sort still do well if they get a head start and grazers are excluded.

Life on land in the Proterozoic: Evidence from the Torridonian rocks of northwest Scotland

The Stoer Group and Diabaig Formation of the Torridonian succession in northwest Scotland are late Mesoproterozoic to early Neoproterozoic (ca. 1200 1000 Ma). Features preserved on the top surfaces of fine- to medium-grained sandstone beds in a number of stratigraphically and geographically separated localities are attributable to microbially induced sedimentary structures; these include wrinkle structures, remnants of apparent microbial crusts, and indications of original cohesiveness and pliancy in sand-sized sediment. The surfaces on which the microbial structures formed were exposed subaerially (abundant, deep desiccation cracks and locally pedogenic structures) in alluvial, interfluve, and lacustrine margin settings, and many of the structures developed in areas well away from the perennially wetted regions adjacent to shorelines and fluvial channels. Thus, these features indicate that Earth's biosphere had adapted to and colonized land surfaces many hundreds of millions of years before the dawn of the Phanerozoic.

There is evidence of ancient soil and even multicellular life of some kind dating from the early - middle Cambrian, also before the date proposed for the forest transplant.

The Great Oxygenation event had reached its final and current stage by 850 million years ago, also before the described transplant. The atmosphere would be close enough to our modern atmosphere for plants.

Hundreds of millions of years of terrestrial microbial mats is plenty of time to make good soil, especially in someplace like an alluvial plain that concentrates the rock breakdown products of these mats. Good soil, good atmosphere, water and light means the forest would thrive.

But what would really thrive are the microbe grazers and their predators. Springtails, slugs and nematodes would quickly spread over the delicious microbe-encrusted earth. These little grazers would move out from the forest and feast on the defenseless microbial mats. Predators that eat these creatures would also have a heyday.

There would be a nice island of forest. The rest of the world would be overrun with bugs until the mats were gone and population crashed.

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