WEBVTT
1
00:00:00.280 --> 00:00:02.960
This is Spacetime Series twenty eight, Episode one hundred and
2
00:00:03.000 --> 00:00:06.240
thirty six for broadcasts on the nineteenth and November twenty
3
00:00:06.280 --> 00:00:10.720
twenty five. Coming up on space Time, the oldest Australian
4
00:00:10.800 --> 00:00:13.839
rocks offering new insights into the origins of the Earth
5
00:00:13.960 --> 00:00:17.800
and the Moon, tantalizing signs of a possible fifth force
6
00:00:17.800 --> 00:00:22.280
in nature, and satellites record twenty meter high ocean waves
7
00:00:22.320 --> 00:00:25.480
on the Earth's surface. All that and more coming up
8
00:00:25.920 --> 00:00:26.879
on space Time.
9
00:00:28.320 --> 00:00:31.480
Welcome to space Time with Stuart Gary.
10
00:00:47.679 --> 00:00:50.600
Scientists have opened a new window into the origins of
11
00:00:50.679 --> 00:00:55.000
Earth's ancient mantling continence. The findings, reported in the journal
12
00:00:55.079 --> 00:00:59.039
Nature Communications, are also providing fresh insights into the early
13
00:00:59.119 --> 00:01:02.479
beginnings of the Moon. The authors reached their findings by
14
00:01:02.520 --> 00:01:06.719
analyzing ancient feldspark crystals within the oldest magmatic rocks ever
15
00:01:06.760 --> 00:01:10.680
found in Australia. They examined three point seven billion euro
16
00:01:10.760 --> 00:01:14.480
and authorosites from the Murchison region of out Back Western Australia.
17
00:01:15.079 --> 00:01:17.920
Now these are the oldest rocks on the Australian continent
18
00:01:18.040 --> 00:01:21.079
and among the oldest on the planet. The studies lead author,
19
00:01:21.200 --> 00:01:24.519
Matilda Boys from the University of Western Australia, says the
20
00:01:24.560 --> 00:01:27.560
timing and rate of early crustal growth on Earth remains
21
00:01:27.599 --> 00:01:31.439
a contentious issue due to the scarcity of very ancient rocks.
22
00:01:32.120 --> 00:01:35.680
Voice and colleagues use fine scale analytical methods to isolate
23
00:01:35.719 --> 00:01:39.439
the fresh areas of pleadiocles feldspark crystals, which record the
24
00:01:39.480 --> 00:01:43.959
isotopic fingerprint of the ancient mantle. The results suggest that
25
00:01:44.040 --> 00:01:47.239
the continents began to grow relatively late in its history,
26
00:01:47.280 --> 00:01:49.480
from around three and a half billion years ago, which
27
00:01:49.519 --> 00:01:52.719
is around a billion years after the planet formed. The
28
00:01:52.760 --> 00:01:56.719
study also compared these results with measurements of lunar northrosites
29
00:01:56.760 --> 00:02:00.959
collected during NASA's Apollo missions. Boys and North rest sites
30
00:02:01.000 --> 00:02:04.200
are rare on Earth but common on the Moon. She says.
31
00:02:04.200 --> 00:02:07.280
The findings are consistent with the Earth and Moon having
32
00:02:07.359 --> 00:02:10.280
the same starting composition around four and a half billion
33
00:02:10.360 --> 00:02:13.759
years ago. Boys says it supports the idea that a
34
00:02:13.840 --> 00:02:16.759
Mars sized planet, which we now call Fear, collided with
35
00:02:16.840 --> 00:02:20.560
the early proto Earth, building both bodies together into a
36
00:02:20.639 --> 00:02:25.199
magma osian an. Ejected debris from that impact event eventually
37
00:02:25.280 --> 00:02:27.439
coalescing into orbit to form the Moon.
38
00:02:27.680 --> 00:02:29.719
The question that we want to urge right is looking
39
00:02:29.759 --> 00:02:34.039
into when the earliest continents grew on Earth, and one
40
00:02:34.080 --> 00:02:36.560
way of doing that is to look at the chemistry
41
00:02:36.680 --> 00:02:39.159
of the mantles through time, because the Earth is the
42
00:02:39.159 --> 00:02:41.439
only planet that we know of that has late tectonics
43
00:02:41.439 --> 00:02:44.560
and it's really been quite integral and the development of
44
00:02:44.599 --> 00:02:47.240
life on Earth and all the other really unique aspects
45
00:02:47.280 --> 00:02:50.439
of our planet. But looking at old mantle drived rocks
46
00:02:50.479 --> 00:02:53.639
is quite difficult because we don't have much left preserved
47
00:02:53.680 --> 00:02:56.439
from that time period. But in Australia and particularly in
48
00:02:56.479 --> 00:02:58.879
Western Australia and in the Murchison region, we've got some
49
00:02:59.000 --> 00:03:01.240
of the oldest rock on Earth. These are the oldest
50
00:03:01.319 --> 00:03:04.400
rocks in Australia three point seven billion years old and
51
00:03:04.439 --> 00:03:06.680
also some of the best preserves of this age. So
52
00:03:06.960 --> 00:03:09.719
what we were doing is looking at these magmatic rocks
53
00:03:09.759 --> 00:03:14.199
that formed from mantle drive magmas, probably underneath an early ocean,
54
00:03:14.360 --> 00:03:16.680
and looking at the chemistry of these rocks, and then
55
00:03:16.719 --> 00:03:19.240
looking at how the mantle composition changed through time.
56
00:03:19.599 --> 00:03:21.560
Was it the jack Hills area? Can I describe it
57
00:03:21.680 --> 00:03:24.520
like that? Or is that overly simplistic and too broad?
58
00:03:24.719 --> 00:03:27.919
Very close to the jack Hills, all around those areas,
59
00:03:28.000 --> 00:03:31.639
it's beautiful country. We took vehicles from the Geological Survey
60
00:03:31.680 --> 00:03:34.479
and we camped out there myself with my PhD supervisor
61
00:03:34.599 --> 00:03:37.479
for a couple of months over a few field seasons
62
00:03:37.639 --> 00:03:40.479
and camping out in swags and looking for these old rocks,
63
00:03:40.479 --> 00:03:43.039
a type of rock called and Autho site. So it's
64
00:03:43.039 --> 00:03:45.280
a rock mostly made of plagia players and they're quite
65
00:03:45.759 --> 00:03:48.280
uncommon rocks on it, but they're actually what makes up
66
00:03:48.319 --> 00:03:50.240
most of the lunar crust, which is quite interesting.
67
00:03:50.319 --> 00:03:51.840
But they're fairly rare on Earth.
68
00:03:51.960 --> 00:03:54.319
That's right, that's right. They formed in slightly different ways
69
00:03:54.319 --> 00:03:57.039
from the lunar ones, but they're quite interesting. They're very distinctive.
70
00:03:57.039 --> 00:04:01.120
They've got these enormous round crystals, white crystal, the old
71
00:04:01.159 --> 00:04:03.120
Earth ones, so they kind of stick out when you
72
00:04:03.159 --> 00:04:05.840
see them walking around and the merchans in it. There's
73
00:04:05.879 --> 00:04:08.639
not much rock exposed. It's quite dusty and kind of
74
00:04:08.639 --> 00:04:10.319
blow scrub and then you see these kind of the
75
00:04:10.560 --> 00:04:13.039
crystals sticking out. It's quite quite unique looking.
76
00:04:13.199 --> 00:04:15.840
What did that tell you about the age of the continents.
77
00:04:15.879 --> 00:04:17.839
So the techniques that we were looking at, we were
78
00:04:17.879 --> 00:04:22.560
looking at radiogenic isotope systems, particularly strong tium isotopes and
79
00:04:22.959 --> 00:04:25.240
calcium isotopes, and the way that these work, you can
80
00:04:25.360 --> 00:04:28.360
use it to date rocks. So for young materials like fossils,
81
00:04:28.439 --> 00:04:31.040
carbon dating is quite a well known technique, and then
82
00:04:31.079 --> 00:04:33.879
for very old things we can use things like geranium,
83
00:04:33.959 --> 00:04:36.959
leads or strontium. But the other useful thing with these
84
00:04:37.120 --> 00:04:40.959
radiogenic isotope systems is that given that we know how
85
00:04:41.040 --> 00:04:43.439
long that these systems decay the half life, we know
86
00:04:43.519 --> 00:04:45.959
that quite well, we can actually knowing the age of
87
00:04:45.959 --> 00:04:47.959
the rocks as well. I was already dated them. We
88
00:04:48.000 --> 00:04:50.480
can get the sort of fingerprints of the rocks from
89
00:04:50.480 --> 00:04:53.519
when it crystallized, and because these are mantle derived rocks,
90
00:04:53.639 --> 00:04:56.040
the fingerprints that we measure and these rocks gives us
91
00:04:56.040 --> 00:04:58.199
the composition of the mantle. If we look at a
92
00:04:58.319 --> 00:04:59.959
range of these rocks, if we know that they're well
93
00:05:00.040 --> 00:05:02.800
preserved and has been really careful to select the best
94
00:05:02.800 --> 00:05:05.480
preserved materials and target them quite carefully, which is what
95
00:05:05.519 --> 00:05:07.839
we did, we can look at how this mantle composition
96
00:05:07.959 --> 00:05:10.560
changed through time. Because when the Earth kind of when
97
00:05:10.560 --> 00:05:13.360
it first formed, it would have been fairly uniform. Before
98
00:05:13.360 --> 00:05:15.839
we had these continents, it would have been mostly primitive
99
00:05:15.839 --> 00:05:19.279
mantles what we call it. Then, as the crust grows,
100
00:05:18.959 --> 00:05:21.879
as the mantle has melted, and as magmas come out,
101
00:05:22.000 --> 00:05:25.160
certain elements go into those magmas preferentially, which means that
102
00:05:25.279 --> 00:05:28.879
actually the composition of the mantle gradually changes through time.
103
00:05:29.000 --> 00:05:31.199
So that's what we're looking for. What we found from
104
00:05:31.240 --> 00:05:34.040
these rocks from the Murchisons is these really old three
105
00:05:34.040 --> 00:05:36.600
point seven billion year old and AUTHO site, is that
106
00:05:36.680 --> 00:05:40.319
the mantle composition was close to that of the bulk Earth,
107
00:05:40.480 --> 00:05:42.879
which means that there hadn't been much continental growth at
108
00:05:42.879 --> 00:05:45.560
all by that stage. But then what we found through time,
109
00:05:45.680 --> 00:05:49.120
so coming into three point five three billion years ago,
110
00:05:49.240 --> 00:05:52.279
we start to see the crustal signature emerge, which is
111
00:05:52.360 --> 00:05:55.199
what we call a depleted mantle signature. So what we
112
00:05:55.279 --> 00:05:58.120
found is that actually the growth of this continents it
113
00:05:58.120 --> 00:06:01.040
didn't start straight away quite a bit of time, So
114
00:06:01.160 --> 00:06:03.439
the first billion years of the Earth's history or so
115
00:06:03.879 --> 00:06:06.839
was probably not a whole lot of continental crust around
116
00:06:06.879 --> 00:06:07.560
at that stage.
117
00:06:07.639 --> 00:06:10.560
So the crust was formed as this convection took place
118
00:06:10.600 --> 00:06:13.560
in the matter, that's right, Yeah, and the lighter materials
119
00:06:13.560 --> 00:06:15.480
stayed on the surface. That's where we get a lot
120
00:06:15.480 --> 00:06:16.920
about granitic rocks.
121
00:06:16.720 --> 00:06:20.160
That's right. And on the modern Earth we know quite
122
00:06:20.199 --> 00:06:23.079
well how these processes formed. We have these plate tectonic
123
00:06:23.160 --> 00:06:26.839
systems operating with continents growing and then ocean neck crust
124
00:06:27.000 --> 00:06:30.199
betting producted and destroyed. But in the early Earth it
125
00:06:30.279 --> 00:06:32.519
might have looked really different, and we don't really know.
126
00:06:32.839 --> 00:06:35.079
There's lots of theories, but we don't know for sure
127
00:06:35.240 --> 00:06:38.120
whether it was a process similar to modern plate tectonics
128
00:06:38.199 --> 00:06:40.759
or something completely different. And probably the Earth looked very
129
00:06:40.759 --> 00:06:42.879
different to how it did today. It would have had
130
00:06:42.920 --> 00:06:45.319
a lot more ocean, a lot of just low lying
131
00:06:45.480 --> 00:06:48.600
the saltic lava, and then probably from about the three
132
00:06:48.839 --> 00:06:53.639
billion year ago, market started forming granite continents and large
133
00:06:53.680 --> 00:06:56.120
stuff from the ocean, and that became kind of more
134
00:06:56.120 --> 00:06:58.560
exposed and started becoming a bit more like the modern
135
00:06:58.560 --> 00:06:59.480
Earth over time.
136
00:06:59.279 --> 00:07:01.360
Gradually, did you do the analysis?
137
00:07:01.480 --> 00:07:03.839
We already knew the age of these rocks by uranium
138
00:07:03.920 --> 00:07:06.399
leads that had been done previously, actually back in the
139
00:07:06.680 --> 00:07:09.800
eighties and nineties for what we did with our strongti misotopes.
140
00:07:09.839 --> 00:07:13.519
Because these rocks have been very old, have been varied
141
00:07:13.680 --> 00:07:15.959
steps and brought back up, and fluids have gone through them.
142
00:07:15.959 --> 00:07:18.120
They've had a really complicated life, so we had to
143
00:07:18.120 --> 00:07:20.920
be able to target the domains that were fresh and
144
00:07:21.000 --> 00:07:25.560
preserve their magmatic compositions really precisely quite our high spatial resolution.
145
00:07:25.720 --> 00:07:27.839
So what we did we have a system that's called
146
00:07:27.920 --> 00:07:31.519
laser eblation mass spectrometry, So we have a mass spectrometer
147
00:07:31.600 --> 00:07:35.160
which is able to measure isotopes of the same elements,
148
00:07:35.199 --> 00:07:37.199
so different masses of the same element, and then we
149
00:07:37.240 --> 00:07:39.079
can look at the ratio of that and that's hooked
150
00:07:39.160 --> 00:07:41.439
up to a laser system, so we can go at
151
00:07:41.560 --> 00:07:44.199
quite a fine scale in these crystals which were imaged
152
00:07:44.360 --> 00:07:47.240
via various different microscopy techniques, and then we look with
153
00:07:47.800 --> 00:07:50.959
this labor and we can ablate quite small areas of
154
00:07:51.000 --> 00:07:53.759
these crystals out and then put that through a mass spectrometers.
155
00:07:53.879 --> 00:07:56.839
We did both that and then we also used essentially
156
00:07:57.040 --> 00:08:00.160
a dentistry thrill and we've drilled out slightly larger thection
157
00:08:00.519 --> 00:08:02.759
of these fresh crystals and we dissolve them up. This
158
00:08:02.920 --> 00:08:05.240
was done actually at the Universe of Bristol in England,
159
00:08:05.279 --> 00:08:08.000
so we used this little dentistry drill and drilled out
160
00:08:08.000 --> 00:08:10.560
the fresh bits of these crystals and then we dissolve
161
00:08:10.639 --> 00:08:13.360
them up in an acid and purified them, so we
162
00:08:13.519 --> 00:08:15.439
just had the elements that we wanted to analyze, and
163
00:08:15.480 --> 00:08:17.600
then again we was used the mass spectrometer for that.
164
00:08:17.639 --> 00:08:19.759
So really the key with these techniques is that you
165
00:08:19.839 --> 00:08:22.000
have to find with these really old socks that are
166
00:08:22.000 --> 00:08:25.240
super complicated, the best preserved areas that you can then
167
00:08:25.279 --> 00:08:28.879
target them really carefully and precisely. So that's what we did.
168
00:08:29.000 --> 00:08:31.920
There's a lot of debate about when play tectonics began.
169
00:08:32.080 --> 00:08:34.399
How does your research go towards resolving that.
170
00:08:34.600 --> 00:08:36.559
It's a very kind of contentious topic and there's a
171
00:08:36.600 --> 00:08:38.759
lot of debate around that, and there's one school of
172
00:08:38.799 --> 00:08:41.679
thought that that kind of argues that these processes began
173
00:08:42.039 --> 00:08:45.080
almost immediately, so that are formed four and a half
174
00:08:45.080 --> 00:08:47.519
billion years ago, and then straight away we started forming
175
00:08:47.559 --> 00:08:49.960
all of these these large contents. From our study, we
176
00:08:49.960 --> 00:08:51.720
think that it took a little bit longer to start.
177
00:08:51.840 --> 00:08:54.840
And the system that we've used, these strontium isotopes, it's
178
00:08:54.840 --> 00:08:57.320
not an approach that's been used before, but actually it
179
00:08:57.320 --> 00:09:00.720
shows a very similar result to other ISOs hope systems
180
00:09:00.720 --> 00:09:03.519
that have been previously applied to different types of rocks,
181
00:09:03.600 --> 00:09:06.039
So it kind of ties in and it agrees with
182
00:09:06.080 --> 00:09:08.440
these other results from different studies. Our point of view
183
00:09:08.440 --> 00:09:10.080
is that it probably took a little bit longer for
184
00:09:10.120 --> 00:09:12.799
these processes to really get going plate tectonics. We might
185
00:09:12.840 --> 00:09:15.639
have had something sort of similar to plate tetonics, but
186
00:09:15.720 --> 00:09:18.000
not exactly the same that it started beginning, and it
187
00:09:18.000 --> 00:09:20.799
probably was a bit of a slow transition.
188
00:09:21.120 --> 00:09:23.879
I would have thought plate tectonics triggered the formation of
189
00:09:23.879 --> 00:09:26.600
the continents, and you couldn't have continents unless plate tectonics
190
00:09:26.759 --> 00:09:28.679
was already happening. Am I right there?
191
00:09:28.759 --> 00:09:32.279
Or there's actually lots of other theories of other ways
192
00:09:32.279 --> 00:09:35.440
to make continents without plate tectonics, that's right, Yeah, So
193
00:09:35.759 --> 00:09:38.639
there's all sorts of names. Some researchers think that a
194
00:09:38.679 --> 00:09:42.200
process called sag duction. So we talk about plate tectonics
195
00:09:42.200 --> 00:09:45.360
as being like a plate to moving a laterally, but
196
00:09:45.480 --> 00:09:48.919
there could have been some sort of vertical system instead.
197
00:09:49.000 --> 00:09:50.799
So what that would mean is that we've got all
198
00:09:50.840 --> 00:09:53.240
of these lavas coming up and melting, and then they
199
00:09:53.240 --> 00:09:57.039
start forming these kind of second platforms or plateaus, and
200
00:09:57.080 --> 00:10:00.720
as these get sickened and thickened from gradual eruptions of
201
00:10:00.799 --> 00:10:02.840
more and more magnets, it gets hot enough at the
202
00:10:02.840 --> 00:10:05.519
base of these big piles to actually start melting and
203
00:10:05.600 --> 00:10:09.120
forming quintet magnets. So that's one method that could have
204
00:10:09.200 --> 00:10:11.960
made these early continents without plate tectonics.
205
00:10:12.039 --> 00:10:14.759
Is that what we see in kratons and hotspots.
206
00:10:14.840 --> 00:10:17.639
That's what we see particularly in the pilbra of Western
207
00:10:17.679 --> 00:10:21.600
Australia and then northwest of Western Australia. That's probably one
208
00:10:21.639 --> 00:10:24.559
of the best examples of that of how continents formed
209
00:10:24.600 --> 00:10:27.720
early on without any clear evidence of plate tectonics. That's
210
00:10:27.759 --> 00:10:28.320
right now you're.
211
00:10:28.240 --> 00:10:30.759
Looking forward to the return of humans to the Moon
212
00:10:30.879 --> 00:10:33.200
because that's where the oldest rocks on Earth have been.
213
00:10:33.159 --> 00:10:37.840
Found, absolutely, and it's been suggested previously that the best
214
00:10:37.840 --> 00:10:40.480
place to find these possibly this kind of had and
215
00:10:40.559 --> 00:10:43.039
records from the Earth is on the Moon itself, because
216
00:10:43.039 --> 00:10:45.080
we've got ancient rocks from the Moon that we've found
217
00:10:45.279 --> 00:10:47.440
on Earth's meteorites, And why couldn't it go the other
218
00:10:47.440 --> 00:10:50.200
way around, Why couldn't we have meteorites from the Earth
219
00:10:50.320 --> 00:10:52.559
sitting on the lunar surface, Which I think is a
220
00:10:52.600 --> 00:10:55.000
really interesting idea in terms of the studies that we
221
00:10:55.080 --> 00:10:57.480
did here with these Earth rocks. We did a comparison
222
00:10:57.519 --> 00:11:00.360
with these ancient lunar rocks, and because there is no
223
00:11:00.759 --> 00:11:04.279
plate tectonics operating on the lunar surface, the ancient crustal
224
00:11:04.320 --> 00:11:07.039
record of the Moon, these really really old rocks that
225
00:11:07.159 --> 00:11:09.320
formed not long after the Moon formed itself, have just
226
00:11:09.320 --> 00:11:11.399
been sitting there on the surface and they have been
227
00:11:11.440 --> 00:11:14.799
impacted by meteorite impacts that have been crushed up a bit.
228
00:11:14.840 --> 00:11:17.240
But we have this quite unique record from the Moon
229
00:11:17.279 --> 00:11:19.399
that we don't have from the Earth from this early period.
230
00:11:19.480 --> 00:11:22.799
So I'm very excited to see what future materials get
231
00:11:22.799 --> 00:11:24.519
brought back from future missions for sure.
232
00:11:24.600 --> 00:11:28.960
That's Matilda Boyce from the University of Western Australia and
233
00:11:29.080 --> 00:11:33.159
this is space time still to come. Scientists may have
234
00:11:33.200 --> 00:11:36.519
found the first tantalizing hints of a possible fifth force
235
00:11:36.559 --> 00:11:41.759
in nature, and satellites record twenty meters high waves socians
236
00:11:41.840 --> 00:11:44.720
or that and more still to come on space time.
237
00:12:00.759 --> 00:12:03.799
Scientists may have found the first tantalizing hints of a
238
00:12:03.840 --> 00:12:07.360
possible fifth force in nature. A report in the journal
239
00:12:07.360 --> 00:12:12.000
Physical Review Letters claims physicists using five calcium isotopes tracked